Assessment of microfilaremia in ‘hotspots’ of four lymphatic filariasis endemic districts of Nepal during post-MDA surveillance

Pramod Kumar Mehta; Mahendra Maharjan

doi:10.1371/journal.pntd.0011932

. 2024 Jan 31;18(1):e0011932. doi: 10.1371/journal.pntd.0011932

Assessment of microfilaremia in ‘hotspots’ of four lymphatic filariasis endemic districts of Nepal during post-MDA surveillance

Pramod Kumar Mehta ^1,^*, Mahendra Maharjan ^1,^*

Editor: Jeremiah M Ngondi²

PMCID: PMC10861036 PMID: 38295107

Abstract

Background

The lymphatic filariasis (LF) elimination program in all sixty-three endemic districts of Nepal was based on annual mass drug administration (MDA) using a combination of diethylcarbamazine (DEC) and albendazole for at least 5 years. The MDA program was started in the Parsa district of the Terai region and at least six rounds of MDA were completed between 2003 and 2017 in all filariasis endemic districts of Central Nepal. Transmission Assessment Survey (TAS) report indicated that circulating filarial antigen (CFA) prevalence was below the critical value i.e., ≤ 2% in selected LF endemic districts of Central Nepal. Based on the TAS report, antigen-positive cases were found clustered in the foci of those districts which were considered as “hotspots”. Hence the present study was designed to assess microfilaremia in hotspots of four endemic districts of Central Nepal after the MDA program.

Methodology and principal findings

The present study assessed microfilaremia in hotspots of four endemic districts i.e. Lalitpur and Dhading from the hilly region and Bara and Mahottari from the Terai region of Central Nepal. Night blood samples (n = 1722) were collected by finger prick method from the eligible sample population irrespective of age and sex. Community people’s participation in the MDA program was ensured using a structured questionnaire and chronic clinical manifestation of LF was assessed using standard case definition. Two districts one each from the hilly region (Lalitpur district) and Terai region (Bara district) showed improved microfilaria (MF) prevalence i.e. below the critical level (<1%) while the other two districts are still over the critical level. There was a significantly high prevalence of MF in male (p = <0.05) and ≥41 years of age group (p = <0.05) community people in the hotspots of four endemic districts. People who participated in the previous rounds of the MDA program have significantly low MF prevalence. The upper confidence limit of MF prevalence in all hotspots of four districts was above the critical level (>1%). Chronic clinical manifestation of LF showed significant association with the older age group (≥41 years) but not with sex.

Conclusions

The study revealed LF transmission improved in hotspots of two districts while continued in others but the risk of LF resurgence cannot be ignored since the upper confidence level of MF prevalence is over 1% in all the hotspots studied districts. High MF prevalence is well correlated with the number of MDA rounds but not with the MDA coverage. Community people involved in MDA drug uptake in any previous and last rounds have significantly less MF infection. Hence it is recommended that before deciding to stop the MDA rounds it is essential to conduct the MF survey at the hotspots of the sentinel sites.

Author summary

Lymphatic filariasis is a neglected tropical disease that causes disability to human beings and is caused by a group of filarial nematodes such as W. bancrofti, Brugia malayi, and Brugia timori while these parasites are transmitted by different species of vector mosquitoes. Nepal government started the MDA program in 2003 and has completed 6–11 rounds of anti-filarial medicine with DEC and albendazole between 2007 and 2022 in selected endemic districts of Central Nepal. TAS report showed a low level of infection (<2%) in all study districts. Interestingly we found that the antigen-positive cases were clustered in foci. We defined those circulating filarial antigen (CFA) positive clustered areas as hotspots and assessed MF infection among the adult community people after the MDA program. The result revealed evidence of MF prevalence above threshold in the hotspots of two districts one each from the hilly region (Dhading district) and Terai region (Mahottari district) even after the completion of the MDA program. In those areas, alternative treatment strategies should be employed to reduce the active infection which can serve as reservoirs for recrudescence transmission. Hence it is urgently needed to identify and screen MF infection among community individuals of hotspots after completion of the MDA program even in other districts.

Introduction

Lymphatic Filariasis (LF) is a neglected tropical disease caused by a group of filarial nematodes most commonly by Wuchereria bancrofti and is transmitted by Culex, Anopheles, and Aedes species of mosquitoes [1,2]. LF is commonly known as elephantiasis which causes disability and disfiguring to human beings due to blocking the lymph vessels by dead microfilariae [3,4].

LF is a major public health problem in tropical and sub-tropical countries of the world. It was estimated that approximately 120 million people from more than 83 tropical and sub-tropical countries were affected by LF along with one billion people at risk of infection in 2000 [5]. Out of those at risk of infection, 65% were from Southeast Asia, 30% were from Africa, and the remaining lived in other tropical countries of the world [6,7]. But recently WHO estimated over 882 million people remained threatened in 44 countries worldwide [8].

The Global Program to Eliminate Lymphatic Filariasis (GPELF) was launched in 2000 and achieved significant progress in 60 countries by 2015 [9]. The program was based on the application of annual MDA with a combination of albendazole plus either diethylcarbamazine (DEC) or Ivermectin to all eligible populations in endemic areas with effective treatment coverage of >65% [4,7,10]. In Nepal, the combination of DEC and albendazole was recommended for at least five years to eliminate LF in the endemic districts of the country.

The expected number of MDA rounds during the elimination program depends on the baseline prevalence of infection, MDA compliance and regimens during TAS [10,11]. It has been shown that the reasons for MF persistence in the community are due to non-compliance with medication and poor coverage of MDA [12–16].

Nepal is one of the filariasis endemic country with recorded infection in 63 districts while the remaining 14 districts are unlikely to be endemic because of their mountainous geographical location [17,18], Nepal government had formulated National Task Force (2003-2020AD) and the MDA program was started in 2003 to interrupt the transmission of microfilariae in the community by 2020. Six rounds of MDA were completed in all endemic districts in 2017. TAS is a surveillance tool to determine the LF infection levels are sustained below the critical cut-off value. TAS should be carried out in the age group of 6–7 years children after 5–6 rounds of MDA with drug coverage of 65% or above. If TAS results showed antigen prevalence ≤2% or MF prevalence ≤1% in community individuals indicated that the MDA round could be stopped. The TAS report showed antigenic prevalence was < 2% in 31 districts in 2018 [19]. Nepal government couldn’t achieve the LF elimination goal by 2020 in some districts based on a series of TAS hence the MDA program was extended with the new LF elimination target by 2030. In Central Nepal, MDA was stopped in Dhading and Mahottari districts after six rounds while in Lalitpur and Bara districts, it was stopped after eight and eleven rounds respectively. We have analyzed the status of LF infection in these districts based on baseline prevalence and a series of TAS reports. The baseline prevalence of Dhading and Mahottari districts had a high prevalence of LF compared to Bara and Lalitpur districts. TAS report indicated CFA prevalence ranged from 0.2 to 1.2% (Table 1).

Table 1. Reported LF prevalence during various stages of assessment in four districts of Central Nepal.

Region	Districts	Population	LF antigen prevalence (%)
			Baseline prevalence		Pre-TAS		TAS I		TAS II
			Year	Prevalence	Year	Prevalence	Year	Prevalence	Year	Prevalence
Hilly	Lalitpur	548,401	2008	1.06	2016	0.66	2017	0.21	2019	0.18
Hilly	Dhading	322,751	2001	14.7٭	2012	0.8	2013	0.8	2017	0.41
Terai	Bara	743,950	2001	0.6	2012	0.0	2013	1.2	2017	1.2
Terai	Mahottari	705,838	2001	2.43٭	2012	0.0	2013	0.6	2017	0.7

Open in a new tab

*, Symbols indicate antigen prevalence above the critical cut-off value (≤ 2%).

Although CFA prevalence during TAS indicated below the critical level, we found that the cases were clustered in the community. Those CFA clusters were considered hotspots and hypothesized that there could be the existence of MF carriers. Thus this study was proposed to assess microfilaremia prevalence in hotspots of four endemic districts of Central Nepal.

Methods

Ethics statements

Ethical approval was retrieved from the Nepal Health Research Council (NHRC/Reg.no. 629/2018). Permission for conducting the study was received from the local government. Written consent forms and information sheets were provided to participants (or parents/guardians) in the local language and written consent was obtained from the participants (or parents/guardians).

Study area

TAS report of Epidemiology and Disease Control Division (EDCD) 2017–2018 indicated comparatively high CFA prevalence in four districts of Central Nepal, two districts (Lalitpur (0.21%) and Dhading (0.41%) from the hilly region and two districts, Bara (1.2%) and Mahottari (0.7%) from Terai region. Due to CFA prevalence below the critical level MDA has already been stopped. On the basis of TAS1, we analyzed the CFA prevalence data in each of the sentinel sites and identified the distribution of the cases in the distinct clusters. We found those clusters at Bungmati and Dukuchhap area (local name) of Lalitpur district (five cases), Salyantar of Dhading district (nine cases), Khairawa and Ammadar of Bara district (six cases) and Matihani of Mahottari district (eight cases), which were considered hotspots and MF survey was conducted. Furthermore, we assessed the MDA coverage and total MDA rounds completed between 2007 and 2022 in the selected endemic districts of Central Nepal (Fig 1).

Study population and sampling

We used Geographic Information System (GIS) data from the Department of Commerce of Nepal for the identification of households in the hotspots of four districts of Central Nepal. Our target population was the age group of 10 years and above since the below 10 years age group have never participated in the MDA program and were born after the MDA program. The required sample size from hotspots of each district was determined using the formula: n = Z²pq/L²

Where, n = number of samples

Z = std. normal deviate (1.96 in 95% confidence interval)

p = prevalence of lymphatic filariasis (Probability of LF prevalence is 50%)

q = 1-p = 1–0.5 = 0.50

l = Error of margin = 5% = 0.05

So, n = (1.96)^2*0.50*0.50/(0.05)² = 385

Non response rate = 10% = 385*10/100 = 38.5

So the actual number of samples for microfilaria detection was (n) = 385+38.5 = 423.5~424.

So 424 samples were targeted for the MF survey from hotspots of each selected districts of Central Nepal.

Assuming at least three target group populations in each household, we selected a total of 724 households from the study area. From each of the hotspots of Lalitpur and Dhading districts from the hilly region, 186 and 174 households were selected respectively. Similarly, 141 and 223 households were selected from Bara and Mahottari districts from the Terai region to obtain the required sample size from each district. ArcGIS software was used to locate selected households and generate printed maps for the MF survey.

The members from the selected houses were enlisted by making a door-to-door visit and estimated the required number of population from each district. A total of 2285 eligible individuals from 724 households were enumerated. People who were outside the house during the study period and who didn’t give consent to participate in the study were excluded. Finally, a total of 1722 individuals were screened for the MF.

Using the structured questionnaire MDA compliance was assessed along with their demographic information. Each of them was asked whether they had swallowed anti-filarial drugs in the last round of MDA and drug uptake in any previous rounds of MDA. Chronic clinical manifestations of LF among the sampled population such as elephantiasis and hydrocele were privately assessed by authorized medical officers of the respective health post. Based on standard case definition, long-term swelling of legs, hands, breasts etc. was considered elephantiasis and scrotum swelling was considered hydrocele (S1 Fig).

Night blood survey for MF prevalence

A total of 1722 night blood samples were collected between 10 PM to 4 AM due to the nocturnal periodicity of Wuchereria bancrofti. Written consent was taken from all the individuals and parents of children below 15 years. The standard finger-prick method was applied briefly, the third or fourth finger of the left hand was cleaned with the alcohol putting the palm upward, air dried and pricked with a sterile lancet towards the internal side of the finger. The first drop of the blood was wiped away with dry cotton wool by applying gentle pressure to the finger. Three drops of blood were collected onto three portions of the single slide (S2 Fig).

Each drop of the blood was spread with the edge of another clean slide making a thick blood film. The slides with blood film were air-dried for about 12 to 24 hours and transported to the laboratory for further analysis. Slide numbers were marked in the corner of the slide using a lead pencil. In the laboratory, blood films were dehaemoglobinized using distilled water for about three minutes. Blood films were air dried, and fixed in acid-alcohol (2 parts of the con. HCL + 98 parts of methyl alcohol). Stained with Giemsa stain for 1–2 minutes and washed in distilled water.

After air drying the blood smear was examined under a compound microscope using a 10X objective. The entire blood smear was examined systematically from one end to the other end. The species of MF was confirmed using 40X objectives (S3 Fig).

The results were entered along with the number of MF against the ID number in the log book. Technical staff cross-examined all the positive and 5% of the negative slides. MF-positive cases were treated with a standard dose of DEC (6 mg/kg body weight) for 12 days under the supervision of an authorized medical officer. (Fig 2).

Statistical analysis

Data were entered in Excel spreadsheets (Microsoft Excel 2007) and subsequently analyzed with Minitab 17 version 19.2.0. Blood test results for MF, the presence of hydrocele or elephantiasis, demographic characteristics, and MDA compliance (site-based, district-wise) were compared by using the Chi-square test and Fisher’s exact test while a p-value ≤ 0.05 was considered statistically significant. The lower and upper limits of the 95% CI for the prevalence of MF were calculated.

Results

Demographic characteristics of the eligible and sampled population

A total of 2285 individuals were found to be eligible for the MF survey in hotspots of four endemic districts of Central Nepal. Among them, 1722 i.e. 75% of individuals were available and screened for MF using night blood collection by finger prick method. The maximum eligible population was covered from the Lalitpur and Bara districts. The average mean age of the individuals was 38 years in between the age group of 10 to 87 years. A maximum of 54% of females were screened for MF screening (Table 2).

Table 2. Age and sex-wise eligible and sampled population in hotspots of four districts of Central Nepal.

Demographic characteristics			Region				Total no. (%)
			Hilly		Terai
			Lalitpur^# No. (%)	Dhading ^β, No. (%)	Bara^γ^, No. (%)	Mahottari^α, No. (%)
Eligible population	Gender	Male	279 (54.4)	244 (42.8)	210 (44.8)	333 (45.4)	1066 (46.7)
		Female	234 (45.6)	326 (57.2)	259 (55.2)	400 (54.6)	1219 (53.3)
		Total	513	570	469	733	2285
	Age group (Years)	≤ 40	286 (55.8)	298 (52.3)	262 (55.9)	396 (54.1)	1242 (54.4)
		≥ 41	227 (44.2)	272 (47.7)	207 (44.1)	337 (45.9)	1043 (45.6)
		Total	513	570	469	733	2285
Sampled population	Gender	Male	175 (44.5)	175 (40.6)	185 (47.1)	226 (44.8)	761 (44.2)
		Female	219 (55.5)	256 (59.4)	208 (52.9)	278 (55.2)	961 (55.8)
		Total	394	431	393	504	1722
	Age group (Years)	≤ 40	223 (56.6)	235 (54.5)	241 (61.3)	330 (65.5)	1029 (59.8)
		≥ 41	171 (43.4)	196 (45.5)	152 (38.7)	174 (34.5)	693 (40.2)
		Total	394 (76.8)	431 (75.6)	393 (83.8)	504 (68.8)	1722 (75.4)

Open in a new tab

Note

^# Dukuchhap and Bungmati of Lalitpur district

^βSalyantar of Dhading district

^γAmmadar and Khairawa of Bara district

^α Matihani of Mahottari district.

Microfilariae and disease burden in hotspots of Central Nepal

Prevalence of microfilariae and chronic clinical manifestation of LF in Central Nepal

The overall prevalence of microfilariae in hotspots of four endemic districts was 2.9%. The result revealed that MF infection in males was significantly higher compared to females but no significant difference was observed between the age group ≤ 40 and ≥ 41 years. The MF prevalence in two districts one each from the hilly region (Lalitpur district) and the Terai region (Bara district) is lower than a 1% cut off WHO recommends to stop MDA. But in the remaining two districts, Dhading district belonging to the hilly region and Mahottari district belonging to the Terai region showed unexpectedly high MF prevalence i.e. 5.8% and 4.4% respectively. Even though MF prevalence is below the critical level in two districts, the upper confidence limit of MF prevalence in all hotspots of four endemic districts had above critical level (≥ 1%) (Table 3).

Table 3. Prevalence of microfilaremia and chronic clinical manifestation of lymphatic filariasis in Central Nepal.

Characteristic		No. (%) total	No.(%) with MF[95%CI]	X² Value (p-value)	No. (%) with hydrocele^*	Z- value (p-value)	No. (%) with elephantiasis	X² Value (p-value)
Gender	Male	761(44.2)	29 (3.8) (2.6–5.4)	3.749 (0.053)	68 (8.9)	-	30 (3.9)	0.049 (0.825)
	Female	961(55.8)	21(2.2) (1.4–3.3)	3.749 (0.053)	-	-	40 (4.2)	0.049 (0.825)
	Total	1722	50 (2.9) (2.2–3.8)	-	-	-	70 (4.1)	-
Age groups in years	≤40	1029 (59.8)	25 (2.4) (1.6–3.6)	1.919 (0.166)	32(7.0)	2.17 (0.027)	12 (1.2)	50.173 (0.000)
	≥41	693 (40.2)	25 (3.6) (2.4–5.3)	1.919 (0.166)	36(11.8)	2.17 (0.027)	58 (8.4)	50.173 (0.000)
	Total	1722	50 (2.9) (2.2–3.8)	-	68 (8.9)	-	70 (4.1)	-
Hilly districts	Lalitpur^#	394 (47.8)	1 (0.3) (0.01–2.5)	19.541 (0.001)	24 (13.7)	1.17 (0.307)	28 (7.1)	0.006 (0.939)
	Dhading^β	431 (52.2)	25 (5.8) (3.6–8.1)	19.541 (0.001)	32 (18.3)	1.17 (0.307)	30 (7.0)	0.006 (0.939)
	Total	825	26 (3.2) (2.1–4.6)	-	56 (16.0)	-	58 (7.1)	-
Terai districts	Bara^γ	393 (43.8)	2 (0.5) (0.06–1.8)	12.012 (0.001)	8 (4.3)	1.48 (0.148)	7 (1.8)	1.013 (0.314)
	Mahottari ^α	504 (56.2)	22 (4.4) (2.8–6.5)	12.012 (0.001)	4 (1.8)	1.48 (0.148)	5 (1.0)	1.013 (0.314)
	Total	897	24 (2.7) (1.7–4.0)	-	12 (2.9)	-	12 (1.3)	-

Open in a new tab

*Denominator included only males

^# Dukuchhap and Bungmati of Lalitpur district

^βSalyantar of Dhading district

^γAmmadar and Khairawa of Bara district

^α Matihani of Mahottari district.

Chronic clinical manifestation of LF was highly prevalent in hotspots of all four endemic districts. Hydrocele and elephantiasis both cases were found significantly high in the hilly region compared to the Terai region but the disease burden was not significantly different in between the districts of both the hilly and Terai regions. Similarly, both chronic disease burden was found to be significantly high in the age group ≥ 41 i.e. older age group (Table 3).

District-wise prevalence of MF in different age and sex groups

In three districts, Dhading, Bara and Mahottari maximum individuals were screened for MF among the age group 21–30 years. MF infection was observed in all age groups individuals in Dhading districts while the infection was not observed in the age group above 60 years in Mahottari. In both districts high MF prevalence was found in between the age group 41–60 years. Only one and two individuals were found infected with MF in the Lalitpur and Bara districts respectively. Comparatively less infection of MF was found in the age group below 41 years (Fig 3).

Maximum female individuals were covered during MF screening in all four districts. Sex-wise prevalence of MF in males of Dhading district has a high prevalence i.e. 10.3%. While in the Mahottari district belonging to the Terai region, both male and female individuals were almost equally infected (Fig 4).

MDA compliance concerning MF infection and chronic clinical manifestation

All 1722 individuals screened for MF were enrolled in a questionnaire survey with their participation in the MDA program. In all hotspots of four districts, MDA coverage among the study participants were found more than 65% in the last round but in the hotspot of Mahottari district coverage was below 65% in previous MDA rounds. MF prevalence was found significantly high among individuals who have not participated in the both last and previous rounds of MDA except for drug uptake during the last round of MDA in Dhading district.

MDA compliance and the chronic clinical manifestation were not found to be remarkably associated. None of the individuals with hydrocele were found to be infected with MF but two individuals from the Dhading district were found to be infected with MF, who had never participated in the MDA program (Table 4).

Table 4. Site-based district-wise association of MDA compliance with microfilaria infection and chronic clinical manifestation of LF.

Districts	Never participated in MDA rounds	No. (%) total	No.(%) with MF	X² Value (p-value)	No. (%) with hydrocele^*	Z- Value (p-value)	No. (%) with elephantiasis	X² Value (p-value)
Lalitpur^# (n = 394)	Previous MDAs	106 (26.9)	1 (0.9)	-	14 (29.2)	3.05 (0.001)	10 (10.0)	1.018 (0.313)
Lalitpur^# (n = 394)	Last MDA	99 (25.1)	1 (1.01)	-	9 (19.6)	1.22 (0.213)	6 (6.1)	0.191 (0.662)
Dhading^β (n = 431)	Previous MDAs	110 (25.5)	11(10.0)	4.14 (0.042)	14 (30.4)	2.22 (0.024)	11 (10.0)	1.8 (0.18)
Dhading^β (n = 431)	Last MDA	87 (20.2)	8 (9.2)	2.00 (0.157)	14 (40.0)	3.10 (0.001)	7 (8.1)	2.0 (0.157)
Bara^γ (n = 393)	Previous MDAs	83 (21.1)	2 (2.4)	-	4 (10.0)	1.47 (0.068)	2 (2.4)	0.228 (0.633)
Bara^γ (n = 393)	Last MDA	78 (19.8)	2 (2.6)	-	4 (10.3)	1.49 (0.062)	2 (2.6)	0.327 (0.567)
Mahottari^α (n = 504)	Previous MDAs	189 (37.5)	13 (6.9)	4.2 (0.042)	3 (3.6)	1.34 (0.144)	5 (2.7)	8.2 (0.004)
Mahottari^α (n = 504)	Last MDA	174 (34.5)	14 (8.1)	7.8 (0.005)	3 (3.8)	1.39 (0.123)	4 (2.3)	4.5 (0.034)

Open in a new tab

*Denominator included only males

^# Dukuchhap and Bungmati of Lalitpur district

^βSalyantar of Dhading district

^γAmmadar and Khairawa of Bara district

^α Matihani of Mahottari district.

Discussions and conclusion

Under the global program to eliminate lymphatic filariasis, the Nepal government started the MDA program with the combination of DEC and albendazole in 2003. The program was launched in all sixty-three endemic districts, and TAS analysis was performed. Based on TAS indicating antigen prevalence < 2%, the MDA program has completely stopped in 51 districts including Lalitpur and Dhading districts of the hilly region and Bara and Mahottari districts of the Terai region. Earlier studies indicated that school-based TAS is not sufficient to stop MDA due to some limitations [9,10,20]. TAS only reflect the new infection in the community but community-based residual infection of MF plays a crucial role in future resurgence [21]. We analyzed the data of the baseline survey, Pre TAS, TAS I and TAS II in four districts. The highest baseline prevalence was shown in Dhading district followed by Mahottari districts but in all TAS, CFA prevalence showed below critical level including other districts and MDA was stopped. Further analysis of data revealed interestingly CFA cases clustered in distinct localities which were considered hotspots. The clusters of antigen-positive children could be proxy indicators of residual microfilaremia carriers in community people of hotspots.

Community children who were born after the MDA program in study areas have reached around 10 years during the current study and they had never been participated in the program. Around 75% population out of 2285 eligible populations above 10 years were sampled for the MF screening in hotspots of four districts.

Treatment coverage and MDA rounds are crucial components of the LF elimination program. For the MDA program to be effective, high treatment coverage is crucial to meet the elimination target within the rational time frame [22]. A further experimental study suggested that endemic areas where the baseline prevalence of LF is high need high treatment coverage along with the increased number of MDA rounds [23]. However, it seems that in our study districts, only treatment coverage and TAS were considered. In the Dhading and Mahottari districts where baseline prevalence was comparatively high but MDA was stopped only after six rounds whereas in the Lalitpur and Bara districts MDA program was extended up to eight and eleven rounds respectively. We found high MF prevalence in those districts where baseline prevalence was also high and low MDA rounds were applied such as Dhading and Mahottari districts. Considering the persistence of cluster of LF positive cases as hotspots, night blood MF survey of ⁓500 community individuals in those foci needs to be carried out for further identification of LF cases and foci treatment of all individuals in the hotspots is recommended. Hotspots of such districts might need bi-annual treatment along with improved treatment coverage and an increase in the number of MDA rounds [24].

Some studies on the impact of the MDA program on LF transmission and infection in areas where DEC and albendazole medicines were implemented such as in India, Papua New Guinea, Egypt, and American Samoa had documented good progress towards elimination [25–27]. In Nepal, most of the districts showed good progress in the MDA program as we observed in two districts Lalitpur and Bara. We observed LF positive cases in hotspots of two districts Dhading and Mahottari with high MF prevalence in age group 41–60. But sex-wise MF prevalence was not uniform in between the hilly district (Dhading) and Terai district (Mahottari). The high prevalence of MF in males of Dhading district could be due to the frequent national and international economic migration of males while in the Terai region migration could be comparatively less due to sufficient agricultural land and industrial development. Frequently migrating people often miss the drug uptake during the MDA program. However, some of the studies documented that optimal drug uptake during MDA is challenging in LF elimination in most of the endemic areas [28–30]. In the present study, community people’s involvement in any previous round of the MDA program showed comparatively less than their involvement in the last round. The reason could be due to the recall bias as well as some of them had only participated in the last round after returning from economic migration. We found a significantly high MF prevalence in people who had not participated in previous and last MDA rounds.

The probability of LF infection in the hotspots and subsequent community seems to be related to the upper confidence level of MF prevalence at a 95% confidence interval (CI). We found an upper confidence level of LF prevalence above critical value in all hotspots of four districts indicating possible future resurgence. It has been recommended that the upper 95% CI of community CFA prevalence of 2% and School children antibody prevalence of 5% could be provisional critical cut-off values for the elimination of LF rather than the CFA critical cut–off value of TAS in school children [21]. The present study highlights the importance of community-based MF prevalence particularly among the 41–60 years age group less than 1% at 95% upper confidence interval need to be included while deciding provisional cut-off value.

The higher number of chronic clinical manifestations of LF such as hydrocele and elephantiasis cases in the community indicates the existence of LF infection for a long time. Evidence suggests that the cases are generally found in localized form. We were interested to know the MF infection among those populations sampled in the hotspots which could reflect the probable infection resurgence. Out of 68 hydrocele individuals in hotspots of four districts none of them were found infected with MF. Out of 70 elephantiasis individuals in the age group 41–60 years, two individuals tested positive for MF infection. Both of them were from Dhading district and had not participated in the last MDA round which is a clear indication of LF resurgence in the hotspots of Dhading district. Similar results have also been reported in earlier studies indicating a low level of microfilaremia in individuals with elephantiasis and hydrocele [31,32].

Hence it is concluded that the number of MDA rounds depends on the baseline prevalence of LF infection in a particular community. Evaluation of an upper confidence interval of less than 1% at 95% CI is a crucial cut-off value at hotspots to stop MDA during the elimination program is important. During the TAS, the MF survey in the age group 41–60 years needs to be included before deciding to stop MDA.

Supporting information

S1 Fig. Patient with Lymphoedema.

(TIF)

Click here for additional data file.^{(5.5MB, tif)}

S2 Fig. Sample collection by finger prick method for microfilaremia study in the field.

(TIF)

Click here for additional data file.^{(2.3MB, tif)}

S3 Fig. Stained blood in stain rack.

(TIF)

Click here for additional data file.^{(4.7MB, tif)}

Acknowledgments

We are thankful for the study area residents who were involved in this research. We also thank the Epidemiology and Disease Control Division and State Public Health Laboratory, Madhesh Pradesh Janakpurdham, Nepal. We express our deepest thanks to all Female Community Health Volunteers and all technical staff for helping in the collection of blood samples. We would like to show our gratitude to all elected heads of local governments of study areas of Central Nepal for their support in conducting the research. We also immensely thank Dr. Jagannath Adhikari, Birendra Multiple Campus, Chitwan, Pradip Rimal, EDCD, Kathmandu and Rambalak Rai, VBDRTC, Hetauda, Nepal for technical and logistic support.

Data Availability

The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files.

Funding Statement

PKM has received a PhD research grant from the University Grants Commission of Nepal (Award no. PhD/74-75 S and T-17). None of the authors have received a salary from the funders. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

References

1.Heymann DL. Control of communicable diseases manual: American Public Health Association; 2008. [Google Scholar]
2.Nutman TB. Insights into the pathogenesis of disease in human lymphatic filariasis. Lymphatic research and biology. 2013;11(3):144–8. doi: 10.1089/lrb.2013.0021 [DOI] [PMC free article] [PubMed] [Google Scholar]
3.WHO. Lymphatic filariasis key facts Geneva: World Health Organization; 2022. [8 March2023,]. Available from: https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis. [Google Scholar]
4.WHO. Lymphatic filariasis: a handbook of practical entomology for national lymphatic filariasis elimination programs. World Health Organization, 2013. (No.WHO/HTM/NTD/PCT/2013.10). [Google Scholar]
5.Ottesen EA. The global program to eliminate lymphatic filariasis. 2000;5(9):591–4. doi: 10.1046/j.1365-3156.2000.00620.x . [DOI] [PubMed] [Google Scholar]
6.WHO. Preparing and implementing a national plan to eliminate filariasis. World Health Organization, 2000 Contract No.: (WHO/CDS/CPE/CEE/2000.16).
7.WHO. The global program to eliminate lymphatic filariasis: progress report 2000–2009 and strategic plan 2010–2020, Geneva. World Health Organization, 2010. (WHO/HTM/NTD/PCT/2010.6). [Google Scholar]
8.World Health Organization. Lymphatic filariasis. Key facts. Geneva: World Health Organization; 2022. https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis. Accessed 23 April 2023. [Google Scholar]
9.WHO. Global program to eliminate lymphatic filariasis: progress report, 2015, Weakly Epidemiological Record. 2016, 91(39), 441–455 Contract No.: . [PubMed] [Google Scholar]
10.WHO. Global Program to Eliminate Lymphatic Filariasis. Monitoring and epidemiological assessment of mass drug administration. A manual for national elimination programs. Geneva: World Health Organization; 2011. [accessed 9 March 2023]. Available from: https://apps.who.int/iris/handle/10665/44580. [Google Scholar]
11.Kyelem D, Biswas G, Bockarie MJ, Bradley MH, El-Setouhy M, Fischer PU, et al. Determinants of success in national programs to eliminate lymphatic filariasis: a perspective identifying essential elements and research needs. The American Journal of Tropical Medicine and Hygiene. 2008;79(4):480, . [PMC free article] [PubMed] [Google Scholar]
12.Jones C, Tarimo DS, Malecela MN. Evidence of continued transmission of Wuchereria bancrofti and associated factors despite nine rounds of ivermectin and albendazole mass drug administration in Rufiji district, Tanzania. Tanzania Journal of Health Research. 2015;17(2). [Google Scholar]
13.Boyd A, Won KY, McClintock SK, Donovan CV, Laney SJ, Williams SA, et al. A community-based study of factors associated with continuing transmission of lymphatic filariasis in Leogane, Haiti. PLoS neglected tropical diseases. 2010;4(3):e640, doi: 10.1371/journal.pntd.0000640 . [DOI] [PMC free article] [PubMed] [Google Scholar]
14.de Souza DK, Ansumana R, Sessay S, Conteh A, Koudou B, Rebollo MP, et al. The impact of residual infections on Anopheles-transmitted Wuchereria bancrofti after multiple rounds of mass drug administration. Parasites & vectors. 2015;8(1):1–8, doi: 10.1186/s13071-015-1091-z . [DOI] [PMC free article] [PubMed] [Google Scholar]
15.Offei M, Anto F. Compliance to mass drug administration program for lymphatic filariasis elimination by community members and volunteers in the Ahanta West District of Ghana. Journal of Bacteriology & Parasitology. 2014;5(1):1. [Google Scholar]
16.El Setouhy M, Abd Elaziz KM, Helmy H, Farid HA, Kamal HA, Ramzy RM, et al. The effect of compliance on the impact of mass drug administration for elimination of lymphatic filariasis in Egypt. 2007, Dec;77(6):1069–73, . [PMC free article] [PubMed] [Google Scholar]
17.Sherchand JB, Obsomer V, Thakur GD, Hommel M. Mapping of lymphatic filariasis in Nepal. Filaria Journal. 2003;2(1):1–9. doi: 10.1186/1475-2883-2-7 [DOI] [PMC free article] [PubMed] [Google Scholar]
18.Dhimal M, Gautam I, Kreß A, Müller R, Kuch U. Spatio-temporal distribution of dengue and lymphatic filariasis vectors along an altitudinal transect in Central Nepal. PLoS Neglected Tropical Diseases. 2014;8(7):e3035. doi: 10.1371/journal.pntd.0003035 [DOI] [PMC free article] [PubMed] [Google Scholar]
19.Department of Health Services. Annual report 2017–2018. https://dohs.gov.np/annual-report-2074-75/. Accessed 17 March 2023.
20.Harris JR, Wiegand RE. Detecting infection hotspots: Modeling the surveillance challenge for elimination of lymphatic filariasis. PLoS Negl Trop Dis. 2017; 11(5):e0005610. doi: 10.1371/journal.pntd.0005610 [DOI] [PMC free article] [PubMed] [Google Scholar]
21.Rao R U, Samarasekera S D, Nagodavithana K C, Dassanayaka T D, Punchihewa M W, Ranasinghe U S, Weil G J Reassessment of areas with persistent Lymphatic Filariasis nine years after cessation of mass drug administration in Sri Lanka. PLoS Neglected Tropical Diseases, (2017). 11(10), e0006066. doi: 10.1371/journal.pntd.0006066 [DOI] [PMC free article] [PubMed] [Google Scholar]
22.Michael E, Malecela-Lazaro MN, Simonsen PE, Pedersen EM, Barker G, Kumar A, et al. Mathematical modelling and the control of lymphatic filariasis. The Lancet infectious diseases. 2004;4(4):223–34, doi: 10.1016/S1473-3099(04)00973-9 . [DOI] [PubMed] [Google Scholar]
23.Michael E, Malecela-Lazaro MN, Kabali C, Snow LC, Kazura JW. Mathematical models and lymphatic filariasis control: endpoints and optimal interventions. Trends in parasitology. 2006;22(5):226–33, doi: 10.1016/j.pt.2006.03.005 Epub 2006 Mar 27. . [DOI] [PubMed] [Google Scholar]
24.Biritwum N-K, Yikpotey P, Marfo BK, Odoom S, Mensah EO, Asiedu O, et al. Persistent ‘hotspots’ of lymphatic filariasis microfilaraemia despite 14 years of mass drug administration in Ghana. Transactions of The Royal Society of Tropical Medicine and Hygiene. 2016;110(12):690–5. doi: 10.1093/trstmh/trx007 [DOI] [PubMed] [Google Scholar]
25.Ramzy RM, El Setouhy M, Helmy H, Ahmed ES, Abd Elaziz KM, Farid HA, et al. Effect of yearly mass drug administration with diethylcarbamazine and albendazole on bancroftian filariasis in Egypt: a comprehensive assessment. The Lancet. 2006;367(9515):992–9, doi: 10.1016/S0140-6736(06)68426-2 . [DOI] [PubMed] [Google Scholar]
26.Weil GJ, Kastens W, Susapu M, Laney SJ, Williams SA, King CL, et al. The impact of repeated rounds of mass drug administration with diethylcarbamazine plus albendazole on bancroftian filariasis in Papua New Guinea. PLoS Neglected Tropical Diseases. 2008;2(12):e344, doi: 10.1371/journal.pntd.0000344 Epub 2008 Dec 9. . [DOI] [PMC free article] [PubMed] [Google Scholar]
27.Liang JL, King JD, Ichimori K, Handzel T, Pa’au M Lammie PJ. Impact of five annual rounds of mass drug administration with diethylcarbamazine and albendazole on Wuchereria bancrofti infection in American Samoa. The American Journal of Tropical Medicine and Hygiene. 2008;78(6):924–8, . [PubMed] [Google Scholar]
28.Kisoka WJ, Simonsen PE, Malecela MN, Tersbøl BP, Mushi DL, Meyrowitsch DW. Factors influencing drug uptake during mass drug administration for control of lymphatic filariasis in rural and urban Tanzania. PLoS One. 2014;9(10):e109316. doi: 10.1371/journal.pone.0109316.s [DOI] [PMC free article] [PubMed] [Google Scholar]
29.Babu BV, Mishra S. Mass drug administration under the program to eliminate lymphatic filariasis in Orissa, India: a mixed-methods study to identify factors associated with compliance and non-compliance. Transactions of the Royal Society of Tropical Medicine and Hygiene. 2008;102(12):1207–13. doi: 10.1016/j.trstmh.2008.05.023 Epub 2008 Jul 15. . [DOI] [PubMed] [Google Scholar]
30.Gunawardena S, Ismail M, Bradley M, Karunaweera N. Factors influencing drug compliance in the mass drug administration program against filariasis in the Western province of Sri Lanka. Transactions of the Royal Society of Tropical Medicine and Hygiene. 2007; 101(5):445–53. doi: 10.1016/j.trstmh.2006.09.002 Epub 2006. Nov 27. . [DOI] [PubMed] [Google Scholar]
31.Derua YA, Kisinza WN, Simonsen PE. Lymphatic filariasis control in Tanzania: infection, disease perceptions, and drug uptake patterns in an endemic community after multiple rounds of mass drug administration. Parasites & vectors. 2018;11:1–9. doi: 10.1186/s13071-018-2999-x [DOI] [PMC free article] [PubMed] [Google Scholar]
32.Dissanayake S. In Wuchereria bancrofti filariasis, asymptomatic microfilaraemia does not progress to amicrofilaraemic lymphatic disease. International journal of epidemiology. 2001;30(2):394–9. doi: 10.1093/ije/30.2.394 [DOI] [PubMed] [Google Scholar]

PLoS Negl Trop Dis. doi: 10.1371/journal.pntd.0011932.r001

Decision Letter 0

Jeremiah M Ngondi, Francesca Tamarozzi

10 Jul 2023

Dear Mr. Mehta,

Thank you very much for submitting your manuscript "Assessment of microfilaremia in ‘hotspots’ of four lymphatic filariasis endemic districts of Central Nepal" for consideration at PLOS Neglected Tropical Diseases. As with all papers reviewed by the journal, your manuscript was reviewed by members of the editorial board and by several independent reviewers. In light of the reviews (below this email), we would like to invite the resubmission of a significantly-revised version that takes into account the reviewers' comments.

We cannot make any decision about publication until we have seen the revised manuscript and your response to the reviewers' comments. Your revised manuscript is also likely to be sent to reviewers for further evaluation.

When you are ready to resubmit, please upload the following:

[1] A letter containing a detailed list of your responses to the review comments and a description of the changes you have made in the manuscript. Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out.

[2] Two versions of the revised manuscript: one with either highlights or tracked changes denoting where the text has been changed; the other a clean version (uploaded as the manuscript file).

Important additional instructions are given below your reviewer comments.

Please prepare and submit your revised manuscript within 60 days. If you anticipate any delay, please let us know the expected resubmission date by replying to this email. Please note that revised manuscripts received after the 60-day due date may require evaluation and peer review similar to newly submitted manuscripts.

Thank you again for your submission. We hope that our editorial process has been constructive so far, and we welcome your feedback at any time. Please don't hesitate to contact us if you have any questions or comments.

Sincerely,

Jeremiah M. Ngondi, MB.ChB, MPhil, MFPH, Ph.D

Academic Editor

PLOS Neglected Tropical Diseases

Francesca Tamarozzi

Section Editor

PLOS Neglected Tropical Diseases

***********************

Reviewer's Responses to Questions

Key Review Criteria Required for Acceptance?

As you describe the new analyses required for acceptance, please consider the following:

Methods

-Are the objectives of the study clearly articulated with a clear testable hypothesis stated?

-Is the study design appropriate to address the stated objectives?

-Is the population clearly described and appropriate for the hypothesis being tested?

-Is the sample size sufficient to ensure adequate power to address the hypothesis being tested?

-Were correct statistical analysis used to support conclusions?

-Are there concerns about ethical or regulatory requirements being met?

Reviewer #1: - The study objective is clearly articulated but the authors may have to consider consistency in the description of the study objective in various sections: Abstract (line 15,16), Author summary (49-51) and Introduction (90-92).

- The study rightly assesses post-treatment lymphatic filariasis (LF)/W. bancrofti infection by nocturnal microfilaremia(mf) (16,17, 125-127).

- The study compares the mf prevalence with LF baseline, pre-TAS and TAS results to make a conclusion of increasing or decreasing infection. However, the study populations of above 9 years (115) is different from the comparison surveys: baseline survey used above 15 years (205-208), pe-TAS is usually uses above 5 years, TAS is usually in 6-7 years. Similarly, all the comparison surveys tested for filarial antigen (206, Table 4) compared to the mf test conducted in the study. The authors indicate that the selection of study age group was based on WHO recommendation (reference 18). However, a review of this reference did confirm this. WHO 2011 LF M&E guidelines age group recommendation for pre-TAS is > 5 years and TAS is 6-7 years.

- The authors investigated suspected infection hotspots/persistent transmission sites. Hotspots was defined as foci with "a cluster of antigen-positive cases and mf carriers" after pre-TAS and TAS, but cluster of positive antigen cases or mf cases was not defined. A clear definition of number of antigen or mf positives that constitute a cluster and therefore hotspot to merit further investigation after a district has passed pre-TAS or TAS would 1) allow for reproducibility of the study 2) be helpful for identifying priority sites/clusters/communities for post-treatment or post-validation surveillance.

- Study site: The authors stated random selection of survey participants from households, it would be important to readers how the households were selected, and what units the households were selected from e.g., community, sub-district, health area etc. This information is not provided.

- The sample size is adequate as it is comparable to site sample size for pre-TAS

- Ethical considerations were adequately covered.

Reviewer #2: The study is a very important one for the global lymphatic filariasis (LF) community as there is little published research on how to detect and respond to areas of ongoing transmission after mass drug administration (MDA) ends. However, the article and the hypotheses statements do not articulate this framing well. For example, it is unclear throughout how the authors define hotspots and whether they are equivalent to districts or sites/villages. The methodology section of the article needs further details, including how sites were selected, how households within sites were selected, and the sampling framework and data source(s). If sites were selected based on pre-TAS or TAS data, it would be useful to include a brief explanation of those surveys in the paper's background section as well. The question of past participation in MDA is becoming more important and a global effort is ongoing to collect this data. As such, it would be helpful to include the exact questions that were asked about past participation in MDA. It would be useful to know what case definitions were used for hydrocele and elephantiasis and the qualifications of those who examined the participants. In terms of ethics, it would be helpful to know what information/treatment was given to participants with clinical conditions.

Reviewer #3: - This is acceptable. But the English needs editing to improve the content and description.

- Should a T-test be used instead of a chi square test?

--------------------

Results

-Does the analysis presented match the analysis plan?

-Are the results clearly and completely presented?

-Are the figures (Tables, Images) of sufficient quality for clarity?

Reviewer #1: - Analysis matches the analysis plan.

- Results are clearly presented

- Figures and tables are of sufficient quality. Titles of tables 2,3 and 5 may be revised to include LF morbidity (lymphedema and hydrocele). Figure 2 may be clearer with a group bar charts for the 4 districts by year.

Reviewer #2: The data analysis would be more useful at a site, rather than district level, as disease prevalence and past participation in MDA can vary widely at village level. The analysis of 'trends' is inappropriate and should not be included, given that previous surveys all had different methodologies, diagnostic tests, age groups, etc. these prevalence levels cannot be compared. Instead the current cross-sectional prevalence can be compared to the microfilaremia cut off of 1%. In addition, given the issues with economic migrants in Nepal, it would be helpful to see an analysis of those 25% of individuals who did not enroll in the study, if that data was collected from the households. The methods mention that the study collected data on movement patterns but did not include this data in the results section - this is information lacking in the literature about Nepal and critical to the Nepal and India LF programs and should be included.

Following are comments on the tables and figures:

- Figure 2 is not necessary. Would recommend combining the reported coverage as part of a revised Table 4 that includes background information on all districts. This could then be shifted to Table 1 as part of the background of these four districts, not to examine trends but to situate this study in the context of other LF information about the districts. This table could include population; baseline prevalence, diagnostic test and year; pre-TAS 'prevalence' diagnostic test and year; TAS diagnostic test, year, critical cut off and number of positives; and reported MDA coverage by year.

- Current Table 1 would be more useful with rows for each site, and columns for 'eligible' and sampled populations, disaggregated by sex and age group. I would consider having a table with demographic characteristics and a separate table(s) with X2 and p-values.

- Current Table 5 would be helpful to include results by site, as well as breakdown of those treated in last MDA and ever treated by age group and sex as well. Past participation results are usually analyzed by asking about participation in the most recent MDA and in all MDAs, including the most recent. If this was also how the authors analyzed it, their results of 75% in most recent and 72% ever participated do not make sense.

Reviewer #3: - When describing the mf prevalence, it will be useful to provide the percentage per district in the text, in addition to the Table that was provided.

- It would be useful to break the age groupings further to assess whether there were infections in children less than 9 years, and also to show the infection levels in different age categories. e.g. <10, 10-20, 21-30, 31-40, etc... The findings should also be discussed appropriately.

- Check Tables 3 and 4. The mf prevalence in Mahottari is indicated as 4.4 in one Table and 5.4 in the other Table.

- Table 4. *, symbols indicate antigen prevalence above the critical value. there was no mention of assessing antigen prevalence in the methods or results. This is not clear and should be clarified, as it leaves me confused.

--------------------

Conclusions

-Are the conclusions supported by the data presented?

-Are the limitations of analysis clearly described?

-Do the authors discuss how these data can be helpful to advance our understanding of the topic under study?

-Is public health relevance addressed?

Reviewer #1: - The mf prevalence recorded in two of the study sites surveyed in Dhading (5.8%) and Mahottari (5.4) would be concerning to the national program as they are above the expected threshold > 1%. This is an important finding. However, since the survey focused on suspected high prevalence/"hotspots" sites (Figure 1) in districts in post-treatment surveillance phase the authors may limit conclusions to the survey sites/communities rather than the districts (175,176, 231-233).

- The authors observe increasing trend of mf in two districts and otherwise in two other districts (181-184, Table 4). However, this is unsupported by the data presented 1) only one data mf prevalence data point is presented out of the 4 data points 2) data in Table 4 does show increasing mf or antigen prevalence trend for any of the four districts.

- Line 53-55: Authors may need to show how the study findings support recommendation for Xenomonitoring and antigen testing.

- The limitation of the study and analysis were not presented.

Reviewer #2: As mentioned above, analysis of trends is not appropriate to do. Instead, the analysis, discussions and conclusion should focus on who is infected, how that links to past MDA participation, and recommendations on how the national program should respond. In addition, it would be useful to the global community to know the authors' recommendations on how to find 'hotspots', how to investigate them and how to respond in a programmatic context. No limitation section is included - it would be worthwhile to add this to the discussion.

Reviewer #3: No conclusions were provided in the discussion

--------------------

Editorial and Data Presentation Modifications?

Use this section for editorial suggestions as well as relatively minor modifications of existing data that would enhance clarity. If the only modifications needed are minor and/or editorial, you may wish to recommend “Minor Revision” or “Accept”.

Reviewer #1: - Authors to look at consistency in use of LF infection, LF cases

- Effective MDA treatment coverage: ≥65% of total population.

- Duration of last MDA and study may affect recall of question on participation in last MDA (187-189). Not clear time of study and last MDA.

- Reconcile when LF program, MDA started, MDA stopped- 2003/2001, 2017, 2018

- Significance of mf prevalence by sex, age (≥ 41 years); lymphedema by age group: review interpretation of results (169,170) and Table 2 (p-values)

Reviewer #2: This article could benefit from an editor. Given that and the other major revisions stated above, it is not worthwhile to include all the minor modifications here that are needed.

Reviewer #3: - Significant language editing is required to make the paper acceptable for publication.

--------------------

Summary and General Comments

Use this section to provide overall comments, discuss strengths/weaknesses of the study, novelty, significance, general execution and scholarship. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. If requesting major revision, please articulate the new experiments that are needed.

Reviewer #1: The study is important for efforts to leave no foci of infection behind as countries make progress towards elimination of LF as a public health problem. The study is also important as a guide for country programs to target sites for post-treatment and post-validation surveillance. A clear definition of what constitutes a cluster of positive cases of concern to merit further investigation for persistent infection as in this study is fundamental to the manuscript. The authors also need to ensure that all conclusions are supported by the study. Some level of editing for consistency would enhance understanding of readers and flow.

Reviewer #2: The study represents an important entry into the global community about how to detect and respond to areas of potential ongoing transmission after MDA is stopped. However, more details are needed about methodology to understand how they detected these areas, and how they sampled the population. The analysis of the results by comparing with previous surveys is inappropriate. More analysis could be done about who was infected (looking at age, sex, occupation, movement patterns) and how past participation linked to infection status. It would be useful to include a discussion of how to respond to these areas and how the Nepal and other programs might translate this research into programmatic activities. With these major revisions, the study would be significant to the LF community as many programs move into post-MDA surveillance.

Reviewer #3: The authors assessed the mf prevalence in hotspot districts in Nepal, after the cessation of MDA. The findings of the study are interesting and the paper is of importance to the field and sustaining the LF elimination achievements. However, there are a number of issues that need to be addressed before it can be acceptable for publication.

- A strong language editing is recommended

- Kindly provide a more accurate description of the timelines in the abstract and main text. In the abstract, if MDA was started in 2001, that gives 15 rounds of MDA by 2016 and not 6 rounds of MDA. In the methods there is mention of 6 to 11 rounds of MDA from 2007 to 2017. These two different description of the MDA timelines are conflicting.

- Please present the mf data in the abstract.

- Kindly discuss the impact of recall bias on the assessment of MDA participation.

- Under the discussion, a concluding paragraph of the study will be useful.

- Given the results, kindly discuss the limitations of TAS in the decision to stop MDA and what can be done to improve the TAS processes.

--------------------

PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

Figure Files:

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email us at figures@plos.org.

Data Requirements:

Please note that, as a condition of publication, PLOS' data policy requires that you make available all data used to draw the conclusions outlined in your manuscript. Data must be deposited in an appropriate repository, included within the body of the manuscript, or uploaded as supporting information. This includes all numerical values that were used to generate graphs, histograms etc.. For an example see here: http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001908#s5.

Reproducibility:

To enhance the reproducibility of your results, we recommend that you deposit your laboratory protocols in protocols.io, where a protocol can be assigned its own identifier (DOI) such that it can be cited independently in the future. Additionally, PLOS ONE offers an option to publish peer-reviewed clinical study protocols. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols

PLoS Negl Trop Dis. 2024 Jan 31;18(1):e0011932. doi: 10.1371/journal.pntd.0011932.r002

Author response to Decision Letter 0

18 Oct 2023

Attachment

Submitted filename: Answer to comments (2).pdf

Click here for additional data file.^{(370.4KB, pdf)}

PLoS Negl Trop Dis. doi: 10.1371/journal.pntd.0011932.r003

Decision Letter 1

Jeremiah M Ngondi, Francesca Tamarozzi

13 Dec 2023

Dear Mr. Mehta,

Thank you very much for submitting your manuscript "Assessment of microfilaremia in ‘hotspots’ of four lymphatic filariasis endemic districts of Nepal during post-MDA surveillance" for consideration at PLOS Neglected Tropical Diseases. As with all papers reviewed by the journal, your manuscript was reviewed by members of the editorial board and by several independent reviewers. The reviewers appreciated the attention to an important topic. Based on the reviews, we are likely to accept this manuscript for publication, providing that you modify the manuscript according to the review recommendations.

I particular Reviewer #2 indicated that a number of aspects still need clarification, especially regarding the definition of hotspot and the sample size and sampling methodology.

These aspects need addressing.

Please prepare and submit your revised manuscript within 30 days. If you anticipate any delay, please let us know the expected resubmission date by replying to this email.

When you are ready to resubmit, please upload the following:

[1] A letter containing a detailed list of your responses to all review comments, and a description of the changes you have made in the manuscript.

Please note while forming your response, if your article is accepted, you may have the opportunity to make the peer review history publicly available. The record will include editor decision letters (with reviews) and your responses to reviewer comments. If eligible, we will contact you to opt in or out

[2] Two versions of the revised manuscript: one with either highlights or tracked changes denoting where the text has been changed; the other a clean version (uploaded as the manuscript file).

Important additional instructions are given below your reviewer comments.

Thank you again for your submission to our journal. We hope that our editorial process has been constructive so far, and we welcome your feedback at any time. Please don't hesitate to contact us if you have any questions or comments.

Sincerely,

Jeremiah M. Ngondi, MB.ChB, MPhil, MFPH, Ph.D

Academic Editor

PLOS Neglected Tropical Diseases

Francesca Tamarozzi

Section Editor

PLOS Neglected Tropical Diseases

***********************

Reviewer's Responses to Questions

Key Review Criteria Required for Acceptance?

As you describe the new analyses required for acceptance, please consider the following:

Methods

-Are the objectives of the study clearly articulated with a clear testable hypothesis stated?

-Is the study design appropriate to address the stated objectives?

-Is the population clearly described and appropriate for the hypothesis being tested?

-Is the sample size sufficient to ensure adequate power to address the hypothesis being tested?

-Were correct statistical analysis used to support conclusions?

-Are there concerns about ethical or regulatory requirements being met?

Reviewer #1: (No Response)

Reviewer #2: - The definition of hotspot is still slightly unclear. Lines 16-17 note that the TAS in sentinel sites was below threshold. Usually, sentinel sites are sampled in pre-transmission assessment surveys (pre-TAS), while TAS randomly samples ~30 clusters (schools or villages) in a district. The number of positive children in a TAS are compared to a critical cut off (roughly equal to 2% antigenemia) to see if MDA can be stopped. My guess is that TAS in these 4 districts passed, e.g. was less than the critical cut off, but certain clusters had multiple positive cases and these were classified as hot spots and erroneously called sentinel sites. However, this needs to be more explicitly defined in the paper and the abstract, specifically: was pre-TAS or TAS data used to determine hotspots? what constituted multiple positive cases, 2, 3, 4?

- Lines 118-120 The number of positives found in each cluster should be noted

- In the introduction, a short summary of TAS methodology would be appropriate to include around line 90-91.

The specific sampling methods still requires more editing to be understandable. I would recommend discussing sample size and number of households at site level -currently it is discussed in totals, at district and site level and is difficult to follow. Table 2 helps capture some of this at district and total levels. However, if the sample size and the results are truly at site level, the other tables should also be constructed to show site level results.

- Line 135 Methods might flow better to start with required sample size and then discuss the number of households needed to be selected to meet this sample size.

- Line 139 I am not a sampling expert, but expecting 50% LF prevalence in a site (when known prevalence was nearer to 3-5%) seems to be inappropriate.

Lines 185-189 Please include at which levels (site, district, total) these analyses were conducted.

Table 3 - results should be presented by site, not total

Reviewer #3: These are accpetable.

--------------------

Results

-Does the analysis presented match the analysis plan?

-Are the results clearly and completely presented?

-Are the figures (Tables, Images) of sufficient quality for clarity?

Reviewer #1: (No Response)

Reviewer #2: The results are presented by total, by district and sometimes by hilly v Terai. As in the methods section, some clarity should be given in presenting at site level, by district and total. Perhaps a separate section and table could look at hilly v Terai if that is critical to the paper. (I'm not sure what the comparison of two districts within the Terai and two within the hilly region as in Table 3 tells us, other than districts/sites are very different.)

Table 3 - Consider bolding results which are significant so that the reader can easily see which ones were significant.

Lines 205-207 Phrasing such as 'much improvement' implies comparison with previous time points. Since that is not able to do be done due to previous different survey methodologies, rephrase to simply 'Mf prevalence is lower than the 1% cut off WHO recommends to stop MDA.'

Line 236 - 'MDA coverage' usually refers to community coverage. In this instance, I believe the 65% is referring to '65% of the study participants noted they participated in the last MDA.'

- Would recommend including a table that reports by site the percentage of participants who had never participated in any MDA and the percentage Mf positive of those who had never participated in any MDA. To answer this, I think the researchers will have to use only those participants who said no to participating in the last MDA round and those who also said no to participating in any other previous rounds.

Reviewer #3: These are acceptable

--------------------

Conclusions

-Are the conclusions supported by the data presented?

-Are the limitations of analysis clearly described?

-Do the authors discuss how these data can be helpful to advance our understanding of the topic under study?

-Is public health relevance addressed?

Reviewer #1: (No Response)

Reviewer #2: - One complicating factor to this analysis is that Mahottari failed TAS3 in 2019, Bara failed TAS2 in 2017, and Laltipur was split into rural and urban areas for TAS. It's unclear when the data for this study were collected, but given that the article will be published in 2023/2024, they should address how their data links to the above survey results. E.g., line 116 notes that MDA has been stopped, which is not true at present.

- Line 270-271 is unclear to me - please revise.

- Lines 279-281 I believe some of the rounds in Lalitpur did not reach effective coverage (e.g. 65%) so did not count to the 5 rounds needed by WHO in order to move to pre-TAS and then TAS to stop MDA. In addition, please confirm the data on number of rounds before TAS1 - this does not match with other data.

Lines 281-284 Note that WHO has not found evidence that biannual treatment is more effective than annual treatment (see Guidelines for LF treatment). Instead, I wonder if reported coverage was accurate or if there were groups of people not participating who continued to harbor microfilaremia. In addition, are you recommending that if a hotspot is found after TAS passes, that the entire district should restart MDA? Or are you recommending focal treatment be done in that hotspot only?

Line 321 - I would not link baseline prevalence in Nepal to number of rounds needed, given issues with baseline prevalence data collection in Nepal, as well as varying reported and surveyed coverage in individual MDA rounds. Your study wasn't designed to study that association.

Reviewer #3: These are acceptable.

--------------------

Editorial and Data Presentation Modifications?

Reviewer #1: (No Response)

Reviewer #2: Line 49 - spell out Wuchereria

Line 53 - delete 'in sentinel sites'

Line 54 - not sure what is meant by 'residual' - presumably these were the first time the participants were tested for antigen. Delete.

Line 57 - No evidence this is resurgence of infection if we don't have comparable data. instead 'prevalence above threshold'

Line 83 - CFA prevalence during TAS hasn't been used in modeling to determine number of rounds of MDA needed

Lines 113-118 and Table 1 - TAS results should be presented as number positive vs a critical cut off and not as a percentage positive, as due to survey design creating a prevalence from the survey needs a special analysis

Table 1 - Please confirm - I believe baseline prevalence was Mf (and not antigen) in Bara, lalitpur, and Mahottari.

Line 289 - The use of 'resurgence' is likely not appropriate since we don't have Mf data from a similar age group from those sites.

Reviewer #3: (No Response)

--------------------

Summary and General Comments

Reviewer #1: Comments on the first draft have been adequately addressed. The readability of the manuscript has been improved. I

Reviewer #2: In general, the article includes very interesting data but more work is still needed to articulate the definition of hotspots, how the sampling was done, and present the results by site/district/total.

Recommending to do night blood sampling of adults in TAS (cluster based surveys of >1000 people) is likely a recommendation very difficult for most programs to implement. Are there recommendations that could address how to identify and follow up potential hotspots? Do you think it's feasible to do community night blood surveys of ~500 people in hotspots instead? And what would you recommend the program do for follow up, beyond just treating those who were found positive?

Reviewer #3: This is a much improved version of the manuscript. My comments have been addressed. Some minor grammatical errors and language editing is still required. However, I believe these will be covered during the proof stage before publication.

--------------------

PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

Figure Files:

Data Requirements:

Reproducibility:

References

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article's retracted status in the References list and also include a citation and full reference for the retraction notice.

PLoS Negl Trop Dis. 2024 Jan 31;18(1):e0011932. doi: 10.1371/journal.pntd.0011932.r004

Author response to Decision Letter 1

28 Dec 2023

Attachment

Submitted filename: Answer to comments.pdf

Click here for additional data file.^{(207.9KB, pdf)}

PLoS Negl Trop Dis. doi: 10.1371/journal.pntd.0011932.r005

Decision Letter 2

Jeremiah M Ngondi, Francesca Tamarozzi

22 Jan 2024

Dear Mr. Mehta,

We are pleased to inform you that your manuscript 'Assessment of microfilaremia in ‘hotspots’ of four lymphatic filariasis endemic districts of Nepal during post-MDA surveillance' has been provisionally accepted for publication in PLOS Neglected Tropical Diseases.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow up email. A member of our team will be in touch with a set of requests.

Please note that your manuscript will not be scheduled for publication until you have made the required changes, so a swift response is appreciated.

IMPORTANT: The editorial review process is now complete. PLOS will only permit corrections to spelling, formatting or significant scientific errors from this point onwards. Requests for major changes, or any which affect the scientific understanding of your work, will cause delays to the publication date of your manuscript.

Should you, your institution's press office or the journal office choose to press release your paper, you will automatically be opted out of early publication. We ask that you notify us now if you or your institution is planning to press release the article. All press must be co-ordinated with PLOS.

Thank you again for supporting Open Access publishing; we are looking forward to publishing your work in PLOS Neglected Tropical Diseases.

Best regards,

Jeremiah M. Ngondi, MB.ChB, MPhil, MFPH, Ph.D

Academic Editor

PLOS Neglected Tropical Diseases

Francesca Tamarozzi

Section Editor

PLOS Neglected Tropical Diseases

***********************************************************

PLoS Negl Trop Dis. doi: 10.1371/journal.pntd.0011932.r006

Acceptance letter

Jeremiah M Ngondi, Francesca Tamarozzi

29 Jan 2024

Dear Mr. Mehta,

We are delighted to inform you that your manuscript, "Assessment of microfilaremia in ‘hotspots’ of four lymphatic filariasis endemic districts of Nepal during post-MDA surveillance," has been formally accepted for publication in PLOS Neglected Tropical Diseases.

We have now passed your article onto the PLOS Production Department who will complete the rest of the publication process. All authors will receive a confirmation email upon publication.

The corresponding author will soon be receiving a typeset proof for review, to ensure errors have not been introduced during production. Please review the PDF proof of your manuscript carefully, as this is the last chance to correct any scientific or type-setting errors. Please note that major changes, or those which affect the scientific understanding of the work, will likely cause delays to the publication date of your manuscript. Note: Proofs for Front Matter articles (Editorial, Viewpoint, Symposium, Review, etc...) are generated on a different schedule and may not be made available as quickly.

Soon after your final files are uploaded, the early version of your manuscript will be published online unless you opted out of this process. The date of the early version will be your article's publication date. The final article will be published to the same URL, and all versions of the paper will be accessible to readers.

Thank you again for supporting open-access publishing; we are looking forward to publishing your work in PLOS Neglected Tropical Diseases.

Best regards,

Shaden Kamhawi

co-Editor-in-Chief

PLOS Neglected Tropical Diseases

Paul Brindley

co-Editor-in-Chief

PLOS Neglected Tropical Diseases

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

S1 Fig. Patient with Lymphoedema.

(TIF)

Click here for additional data file.^{(5.5MB, tif)}

S2 Fig. Sample collection by finger prick method for microfilaremia study in the field.

(TIF)

Click here for additional data file.^{(2.3MB, tif)}

S3 Fig. Stained blood in stain rack.

(TIF)

Click here for additional data file.^{(4.7MB, tif)}

Attachment

Submitted filename: Answer to comments (2).pdf

Click here for additional data file.^{(370.4KB, pdf)}

Attachment

Submitted filename: Answer to comments.pdf

Click here for additional data file.^{(207.9KB, pdf)}

Data Availability Statement

The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files.

[pntd.0011932.ref001] 1.Heymann DL. Control of communicable diseases manual: American Public Health Association; 2008. [Google Scholar]

[pntd.0011932.ref002] 2.Nutman TB. Insights into the pathogenesis of disease in human lymphatic filariasis. Lymphatic research and biology. 2013;11(3):144–8. doi: 10.1089/lrb.2013.0021 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref003] 3.WHO. Lymphatic filariasis key facts Geneva: World Health Organization; 2022. [8 March2023,]. Available from: https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis. [Google Scholar]

[pntd.0011932.ref004] 4.WHO. Lymphatic filariasis: a handbook of practical entomology for national lymphatic filariasis elimination programs. World Health Organization, 2013. (No.WHO/HTM/NTD/PCT/2013.10). [Google Scholar]

[pntd.0011932.ref005] 5.Ottesen EA. The global program to eliminate lymphatic filariasis. 2000;5(9):591–4. doi: 10.1046/j.1365-3156.2000.00620.x . [DOI] [PubMed] [Google Scholar]

[pntd.0011932.ref006] 6.WHO. Preparing and implementing a national plan to eliminate filariasis. World Health Organization, 2000 Contract No.: (WHO/CDS/CPE/CEE/2000.16).

[pntd.0011932.ref007] 7.WHO. The global program to eliminate lymphatic filariasis: progress report 2000–2009 and strategic plan 2010–2020, Geneva. World Health Organization, 2010. (WHO/HTM/NTD/PCT/2010.6). [Google Scholar]

[pntd.0011932.ref008] 8.World Health Organization. Lymphatic filariasis. Key facts. Geneva: World Health Organization; 2022. https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis. Accessed 23 April 2023. [Google Scholar]

[pntd.0011932.ref009] 9.WHO. Global program to eliminate lymphatic filariasis: progress report, 2015, Weakly Epidemiological Record. 2016, 91(39), 441–455 Contract No.: . [PubMed] [Google Scholar]

[pntd.0011932.ref010] 10.WHO. Global Program to Eliminate Lymphatic Filariasis. Monitoring and epidemiological assessment of mass drug administration. A manual for national elimination programs. Geneva: World Health Organization; 2011. [accessed 9 March 2023]. Available from: https://apps.who.int/iris/handle/10665/44580. [Google Scholar]

[pntd.0011932.ref011] 11.Kyelem D, Biswas G, Bockarie MJ, Bradley MH, El-Setouhy M, Fischer PU, et al. Determinants of success in national programs to eliminate lymphatic filariasis: a perspective identifying essential elements and research needs. The American Journal of Tropical Medicine and Hygiene. 2008;79(4):480, . [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref012] 12.Jones C, Tarimo DS, Malecela MN. Evidence of continued transmission of Wuchereria bancrofti and associated factors despite nine rounds of ivermectin and albendazole mass drug administration in Rufiji district, Tanzania. Tanzania Journal of Health Research. 2015;17(2). [Google Scholar]

[pntd.0011932.ref013] 13.Boyd A, Won KY, McClintock SK, Donovan CV, Laney SJ, Williams SA, et al. A community-based study of factors associated with continuing transmission of lymphatic filariasis in Leogane, Haiti. PLoS neglected tropical diseases. 2010;4(3):e640, doi: 10.1371/journal.pntd.0000640 . [DOI] [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref014] 14.de Souza DK, Ansumana R, Sessay S, Conteh A, Koudou B, Rebollo MP, et al. The impact of residual infections on Anopheles-transmitted Wuchereria bancrofti after multiple rounds of mass drug administration. Parasites & vectors. 2015;8(1):1–8, doi: 10.1186/s13071-015-1091-z . [DOI] [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref015] 15.Offei M, Anto F. Compliance to mass drug administration program for lymphatic filariasis elimination by community members and volunteers in the Ahanta West District of Ghana. Journal of Bacteriology & Parasitology. 2014;5(1):1. [Google Scholar]

[pntd.0011932.ref016] 16.El Setouhy M, Abd Elaziz KM, Helmy H, Farid HA, Kamal HA, Ramzy RM, et al. The effect of compliance on the impact of mass drug administration for elimination of lymphatic filariasis in Egypt. 2007, Dec;77(6):1069–73, . [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref017] 17.Sherchand JB, Obsomer V, Thakur GD, Hommel M. Mapping of lymphatic filariasis in Nepal. Filaria Journal. 2003;2(1):1–9. doi: 10.1186/1475-2883-2-7 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref018] 18.Dhimal M, Gautam I, Kreß A, Müller R, Kuch U. Spatio-temporal distribution of dengue and lymphatic filariasis vectors along an altitudinal transect in Central Nepal. PLoS Neglected Tropical Diseases. 2014;8(7):e3035. doi: 10.1371/journal.pntd.0003035 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref019] 19.Department of Health Services. Annual report 2017–2018. https://dohs.gov.np/annual-report-2074-75/. Accessed 17 March 2023.

[pntd.0011932.ref020] 20.Harris JR, Wiegand RE. Detecting infection hotspots: Modeling the surveillance challenge for elimination of lymphatic filariasis. PLoS Negl Trop Dis. 2017; 11(5):e0005610. doi: 10.1371/journal.pntd.0005610 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref021] 21.Rao R U, Samarasekera S D, Nagodavithana K C, Dassanayaka T D, Punchihewa M W, Ranasinghe U S, Weil G J Reassessment of areas with persistent Lymphatic Filariasis nine years after cessation of mass drug administration in Sri Lanka. PLoS Neglected Tropical Diseases, (2017). 11(10), e0006066. doi: 10.1371/journal.pntd.0006066 [DOI] [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref022] 22.Michael E, Malecela-Lazaro MN, Simonsen PE, Pedersen EM, Barker G, Kumar A, et al. Mathematical modelling and the control of lymphatic filariasis. The Lancet infectious diseases. 2004;4(4):223–34, doi: 10.1016/S1473-3099(04)00973-9 . [DOI] [PubMed] [Google Scholar]

[pntd.0011932.ref023] 23.Michael E, Malecela-Lazaro MN, Kabali C, Snow LC, Kazura JW. Mathematical models and lymphatic filariasis control: endpoints and optimal interventions. Trends in parasitology. 2006;22(5):226–33, doi: 10.1016/j.pt.2006.03.005 Epub 2006 Mar 27. . [DOI] [PubMed] [Google Scholar]

[pntd.0011932.ref024] 24.Biritwum N-K, Yikpotey P, Marfo BK, Odoom S, Mensah EO, Asiedu O, et al. Persistent ‘hotspots’ of lymphatic filariasis microfilaraemia despite 14 years of mass drug administration in Ghana. Transactions of The Royal Society of Tropical Medicine and Hygiene. 2016;110(12):690–5. doi: 10.1093/trstmh/trx007 [DOI] [PubMed] [Google Scholar]

[pntd.0011932.ref025] 25.Ramzy RM, El Setouhy M, Helmy H, Ahmed ES, Abd Elaziz KM, Farid HA, et al. Effect of yearly mass drug administration with diethylcarbamazine and albendazole on bancroftian filariasis in Egypt: a comprehensive assessment. The Lancet. 2006;367(9515):992–9, doi: 10.1016/S0140-6736(06)68426-2 . [DOI] [PubMed] [Google Scholar]

[pntd.0011932.ref026] 26.Weil GJ, Kastens W, Susapu M, Laney SJ, Williams SA, King CL, et al. The impact of repeated rounds of mass drug administration with diethylcarbamazine plus albendazole on bancroftian filariasis in Papua New Guinea. PLoS Neglected Tropical Diseases. 2008;2(12):e344, doi: 10.1371/journal.pntd.0000344 Epub 2008 Dec 9. . [DOI] [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref027] 27.Liang JL, King JD, Ichimori K, Handzel T, Pa’au M Lammie PJ. Impact of five annual rounds of mass drug administration with diethylcarbamazine and albendazole on Wuchereria bancrofti infection in American Samoa. The American Journal of Tropical Medicine and Hygiene. 2008;78(6):924–8, . [PubMed] [Google Scholar]

[pntd.0011932.ref028] 28.Kisoka WJ, Simonsen PE, Malecela MN, Tersbøl BP, Mushi DL, Meyrowitsch DW. Factors influencing drug uptake during mass drug administration for control of lymphatic filariasis in rural and urban Tanzania. PLoS One. 2014;9(10):e109316. doi: 10.1371/journal.pone.0109316.s [DOI] [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref029] 29.Babu BV, Mishra S. Mass drug administration under the program to eliminate lymphatic filariasis in Orissa, India: a mixed-methods study to identify factors associated with compliance and non-compliance. Transactions of the Royal Society of Tropical Medicine and Hygiene. 2008;102(12):1207–13. doi: 10.1016/j.trstmh.2008.05.023 Epub 2008 Jul 15. . [DOI] [PubMed] [Google Scholar]

[pntd.0011932.ref030] 30.Gunawardena S, Ismail M, Bradley M, Karunaweera N. Factors influencing drug compliance in the mass drug administration program against filariasis in the Western province of Sri Lanka. Transactions of the Royal Society of Tropical Medicine and Hygiene. 2007; 101(5):445–53. doi: 10.1016/j.trstmh.2006.09.002 Epub 2006. Nov 27. . [DOI] [PubMed] [Google Scholar]

[pntd.0011932.ref031] 31.Derua YA, Kisinza WN, Simonsen PE. Lymphatic filariasis control in Tanzania: infection, disease perceptions, and drug uptake patterns in an endemic community after multiple rounds of mass drug administration. Parasites & vectors. 2018;11:1–9. doi: 10.1186/s13071-018-2999-x [DOI] [PMC free article] [PubMed] [Google Scholar]

[pntd.0011932.ref032] 32.Dissanayake S. In Wuchereria bancrofti filariasis, asymptomatic microfilaraemia does not progress to amicrofilaraemic lymphatic disease. International journal of epidemiology. 2001;30(2):394–9. doi: 10.1093/ije/30.2.394 [DOI] [PubMed] [Google Scholar]

PERMALINK

Assessment of microfilaremia in ‘hotspots’ of four lymphatic filariasis endemic districts of Nepal during post-MDA surveillance

Pramod Kumar Mehta

Mahendra Maharjan

Roles

Abstract

Background

Methodology and principal findings

Conclusions

Author summary

Introduction

Table 1. Reported LF prevalence during various stages of assessment in four districts of Central Nepal.

Methods

Ethics statements

Study area

Fig 1. Reported treatment coverage during diethylcarbamazine and albendazole MDA intervention in hotspots of the study area.

Study population and sampling

Night blood survey for MF prevalence

Fig 2. Blood film showing microfilaria of W. bancrofti.

Statistical analysis

Results

Demographic characteristics of the eligible and sampled population

Table 2. Age and sex-wise eligible and sampled population in hotspots of four districts of Central Nepal.

Microfilariae and disease burden in hotspots of Central Nepal

Prevalence of microfilariae and chronic clinical manifestation of LF in Central Nepal

Table 3. Prevalence of microfilaremia and chronic clinical manifestation of lymphatic filariasis in Central Nepal.

District-wise prevalence of MF in different age and sex groups

Fig 3. Age-wise distribution of MF in hotspots of four districts of Central Nepal.

Fig 4. Sex-wise distribution of MF in hotspots of four districts of Central Nepal.

MDA compliance concerning MF infection and chronic clinical manifestation

Table 4. Site-based district-wise association of MDA compliance with microfilaria infection and chronic clinical manifestation of LF.

Discussions and conclusion

Supporting information

Acknowledgments

Data Availability

Funding Statement

References

Decision Letter 0

Jeremiah M Ngondi

Francesca Tamarozzi

Roles

Author response to Decision Letter 0

Decision Letter 1

Jeremiah M Ngondi

Francesca Tamarozzi

Roles

Author response to Decision Letter 1

Decision Letter 2

Jeremiah M Ngondi

Francesca Tamarozzi

Roles

Acceptance letter

Jeremiah M Ngondi

Francesca Tamarozzi

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

Similar articles

Cited by other articles

Links to NCBI Databases