Abstract
Malaria continues to pose a significant public health challenge in Cameroon, requiring effective prevention strategies. Long-lasting insecticide-treated nets (LLINs) are widely distributed as a key control measure, but their physical integrity and effectiveness need to be monitored. This study aimed to assess the condition and bio-efficacy of LLINs in 2 regions of Cameroon, namely Santchou in the West and Bertoua in the East. The study evaluated LLIN use and care using a structured questionnaire, following World Health Organization (WHO) guidelines for assessing physical integrity. Bio-efficacy was measured using the 3-min WHO cone assay. The results showed that the ownership and usage rates of mosquito nets were 93.91% and 72.70% in Santchou and 60.68% and 41.11% in Bertoua, respectively. In Santchou, 5.26% of LLINs were damaged, with 21.05% rendered unusable while in Bertoua, 29.41% of the used LLINs were damaged with 16.47% unusable. The knockdown rate with field mosquito populations was 65.49% with mortality rate of 61.24% in Bertoua. In Santchou, knockdown rate was 10.23%, and mortality rate 14.97%. The LLINs tested were found highly effective against susceptible strain. These findings urgently require the National Malaria Control Program of Cameroon to improve public awareness on consistent and proper LLIN usage and address the decline in LLIN effectiveness, particularly in cities like Bertoua and Santchou. Targeted interventions should focus on improving LLINs distribution, educating the population on correct usage practices, and implementing regular monitoring of physical integrity and bio-efficacy of insecticide-treated bed nets as these LLINs get degraded.
Keywords: malaria, long-lasting insecticidal nets, bio-efficacy, Bertoua, Santchou
Introduction
Malaria continues to be a significant public health problem in Africa, where more than 95% of cases and deaths occur (WHO 2022). The most vulnerable groups are children under 5 years old and pregnant women (WHO 2022). Cameroon is among the top 11 countries heavily affected by malaria, and the government’s objective is to reduce malaria-related death and incidence rate by 90% by 2030 in line with the global strategy for malaria elimination (WHO 2016). To achieve this, one of the key strategies implemented is the widespread distribution of long-lasting insecticide-treated nets (LLINs) at no cost. Since 2000, the Ministry of Health through the National Malaria Control Program (NMCP) has conducted 5 major campaigns to distribute impregnated mosquito nets to the population National Malaria Control Programme (NMCP, 2022). These efforts, along with other malaria control measures such as intermittent preventive treatments for pregnant women, early diagnosis, and case management, have led to increased ownership and use of LLINs, resulting in a significant reduction in malaria morbidity and mortality National Malaria Control Programme (NMCP, 2022).
Despite these advancements, malaria remains a major endemic disease in Cameroon, with over 6 million cases and 14,237 associated deaths reported in the country’s health facilities in 2021 (WHO 2022). Several factors contribute to this situation, including the development and spread of insecticide resistance among the mosquito vectors targeted by LLINs (Antonio-Nkondjio et al. 2019), changes in vector behavior, such as increased biting activity outside of homes or during times when people are not protected by mosquito nets and none or low utilization of LLINs by populations (Bamou et al. 2018).
LLINs are primarily a physical barrier against mosquito bites. This protection is enhanced when the bed net is treated with an insecticide that deters, repels, or kills vectors that attempt to bite the sleeper (Mutuku et al. 2013). It is therefore clear that in order to fully play this role, the mosquito net must have good physical integrity and the insecticide used for its impregnation must have proven efficacy (Nopowo 2020). While LLINs are expected to remain effective for approximately 3 yr under natural conditions according to the WHO Pesticide Evaluation Scheme (WHOPES), studies conducted in certain localities in Cameroon have shown otherwise (Boussougou-Sambe et al. 2017, Djoufounna et al. 2022, Ngongang-Yipmo et al. 2022, Efa et al. 2024).
In Cameroon, the mass distribution campaign of LLINs was implemented in 2011, with about 8,654,731 LLINs distributed throughout the country (Boussougou-Sambe et al. 2017). This was followed by a second mass distribution in 2015 and a third with the distribution of about eight million LLINs in 2019 (WHO 2020). However, there was a lack of monitoring of these LLINs the year following their distribution. The WHO recommends that malaria control programs conducting mass LLINs distribution campaigns should systematically monitor the durability of LLINs under real usage conditions, following established protocols (WHO 2015). This recommendation aims to provide countries with factual data to guide LLIN selection, determine campaign frequency, and identify population practices that may impact the lifespan of LLINs. Furthermore, regular monitoring of LLINs is crucial for the success of vector control measures, as it enables the prompt identification of any deterioration over time and facilitates the implementation of appropriate interventions.
Santchou and Bertoua, 2 distinctive localities within the mosaic of Cameroon’s diverse landscape, confront the persistent threat of malaria, a high public health concern that disproportionately affects communities across the country (Chouakeu et al. 2023). In response to this continuing battle, the strategic deployment and utilization of LLINs have emerged as pivotal tools in the fight against malaria within these specific regions. Understanding the bio-efficacy of LLINs in Santchou and Bertoua holds profound implications for localized malaria prevention strategies and public health policy. The study aims to underscore the significance of comprehending LLINs effectiveness 1 yr after the 2019 distribution campaign, as a pivotal factor in tailored malaria control strategies and community-based public health endeavors within these specific locales.
Materials and Methods
Study Sites
The study was conducted nets in Santchou (June 2020) and Bertoua (November 2021), 1-yr post mass distribution of bed (Fig. 1). Details on the characteristics of these study sites are presented in Table 1 (Chouakeu et al. 2023).
Fig. 1.
Map of the study sites.
Table 1.
Description of the study sites
| Characteristics | Santchou | Bertoua |
|---|---|---|
| Name of Region | West | East |
| Name of Division | Menoua | Lom et Djérem |
| Coordinates | 5°16′55″N, 9°58′27″E | 4°34′30″N, 13°41′04″E |
| Domain | Highland Grassfields | Forest zone |
| Urban/rural | Rural | Urban |
| Altitude | 750 m above sea level | 400 m above sea level |
| Climate | Equatorial | Subtropical |
| Average Temperature | 23 °C | 26 °C |
| Seasons | A long rainy season (8 mo) and short dry season (4 mo) | 4 seasons 2 rainy 2 dry |
| Vegetation | Grassland | Semi calducifoliated dense forest |
| Main Ethnic groups | Mbô, Bamiléké, and Bamoun | Beti, Hausa, Baka, Bamileké |
| Main activities | Agriculture and small business | Civil servants & small business |
| Religion | >80% Christian | 30% Muslim 70% Christian |
| Endemic stratum | Hypoendemic | Mesoendemic |
| Entomological inoculation rate | 0.03–2.24 infected bites/person/month (Amvongo-Adjia et al. 2018) | 20–50 infected bites/person/year (Antonio-Nkondjio et al., 2019) |
| Main malaria vectors | An. gambiae | An. gambiae, An. coluzzii |
| Years of LLINs distribution campaigns | 2011, 2015, 2019 | 2011, 2015, 2019 |
Data Collection on Physical Integrity of Mosquito Nets
On the field, the survey was conducted in households of Santchou and Bertoua recording sociodemographic characteristics of the respondents, including sex, level of education, and profession of the head of households. The ownership and usage of nets were also recorded with the various actions related to the use of LLINs, such as the washing tools, the washing frequency, the drying location, the presence or absence of holes, the number of holes, the sides of the nets with holes and the causes of the holes.
The physical integrity of the nets was assessed for the absence or presence of holes on nets retrieved from volunteers. This activity was performed by a team experienced in community surveys. The LLINs retrieved and substituted in both sites were kept individually in plastic bags to avoid any contact and transported to the Vector-Borne Diseases Laboratory of the Research Unit of Biology and Applied Ecology (VBID-RUBAE) of the University of Dschang and Malaria Research laboratory of “Organisation de Coordination pour la lutte contre les Endémies en Afrique Centrale” (OCEAC). Once in the laboratory, the number and size of holes present were counted on each side. The different observed holes were classified into 4 categories based on their size (WHO, 2011): T1, which includes holes with a size ranging from 0.5 to 2.5 cm; T2 for holes ranging from 2.5 to 10 cm; T3 for holes between 10 and 25 cm; and T4 for holes larger than 25 cm.
The categorization of hole types allowed for the calculation of 2 indicators: the proportion of nets with holes [95% CI] and the Hole Index (HI) (WHO, 2011). HI = (a × number of T1 holes) + (b × number of T2 holes) + (c × number of T3 holes) + (d × number of T4 holes). Here, a, b, c, and d represent the weighting factors (a = 1; b = 23; c = 196; d = 578) (WHO 2013). Nets with holes were classified into 3 categories based on the HI:
- Good (0 < HI < 64): No significant reduction in physical integrity compared to a well-maintained LLIN.
- Damaged (65 < HI < 642): Although damaged, the LLIN still provides acceptable physical protection against mosquito bites.
- Unusable (HI > 642): The LLIN’s condition seriously compromises user protection.
Prospecting and Larval Collection of Anopheles Mosquitoes
In each of the study areas, mosquito larvae identified as Anopheles larvae were collected from various types of breeding sites (standing water, neglected swimming pools, clogged rain gutters, puddles, footprints, ponds, furrows, ditches, and the edges of small streams) using the dipping method (Service, 1993). This method involves scooping the water from the breeding site at different locations using a dipper or plate and observing the presence of larvae or pupae. The larval breeding sites were identified during preliminary surveys in the different sites.
The larvae collected in Bertoua and Santchou were transported to the insectarium of the Malaria Research Laboratory of OCEAC (Organization for the Coordination of Control of Endemic Diseases in Central Africa) and the Vector-Borne Disease Research Laboratory (VBID-URBEA) at the University of Dschang respectively. In the insectarium, the larvae were sorted, transferred to trays containing spring water, and fed with fish food (Tetramin) under standard conditions (27 °C ± 2 and RH 70% ± 10) until the pupae stage. The pupae were sorted using a pipette and transferred to emergence cages. Inside the cages, the adults were fed with a 10% glucose solution “ad libitum.”
Description of Nets Used for Bio-efficacy Cones Test
The LLINs used for assays were those obtained for the free distribution campaign of 2019, namely Olyset net in Santchou and Olyset Plus in Bertoua.
Olyset net has 2 basic colors, white and pale blue, and 5 net sizes based on the width. It is made out of wide-meshed high-density polyethylene in which the permethrin is incorporated directly into the fiber at a 2% concentration (corresponding to 1 g/m2 surface concentration).
Olyset Plus is a long-lasting polyethylene mosquito net containing 2% of the pyrethroid insecticide permethrin (800/m2) and 1% (400 mg/m2) of the synergist piperonyl butoxide (PBO).
Evaluation of Bio-efficacy of Olyset and Olyset Plus Net
Cone tests were conducted on selected retrieved mosquito nets following the adapted World Health Organization (WHO) protocol (WHO 2018). Prior to the test, mosquitoes of each species were starved by removing the sucrose solution. Ten cones (2 cones per side) were placed on various sides of each mosquito net. Five to 10 adult female An. gambiae s.l. mosquitoes aged 3 to 5 d were introduced into each cone using a mouth aspirator for contact with the insecticide on the net for 3 min. After exposure, mosquitoes were transferred to holding cups to observe their knockdown rates over 1 h. Cotton pads soaked in a 10% sucrose solution were placed on the sterile netting covering each cup, and all cups were kept under observation for 24 h to record mortality.
The susceptible Kisumu strain was used as a positive control to test for the efficacy of LLINs. The efficacy of nets was determined according to the WHO criteria and was interpreted as follows: mortality ≥ 80% or knockdown ≥ 95% was optimal efficacy; mortality ≥ 50% or knockdown ≥ 75% was minimal efficacy; mortality < 50% or knockdown < 75% was noneffective.
Ethical Approval and Consent to Participate
The study was conducted under the ethical clearance N ° 2020/04/1209/CE/CNERSH/SP delivered by the Cameroon National Ethics (CNE) Committee for Research on Human Health. We also obtained formal authorizations from neighborhood leaders and owners of houses that served as collection points.
Data Analysis
To assess the effectiveness of LLINs, the mosquito mortality rates of the laboratory susceptible strain Kisumu were compared to those of the field strain using a chi-square (χ2) test. For all analyses, tests were considered significant for P < 0.05.
Results
Sociodemographic Characteristics of the Surveyed Population
The sociodemographic characteristics of the surveyed households in Santchou and Bertoua are presented in Table 2. A total of 525 households were surveyed, with 262 in Bertoua and 263 in Santchou. The majority of respondents had a secondary level of education (50.41% and 69.5% in Bertoua and Santchou, respectively). In both locations, most of the interviewed household heads worked in the informal sector (small businesses) (>60%). Various characteristics of the houses were recorded during the study. The majority of houses were constructed with cement blocks in Santchou (82.03%; n = 210) and in Bertoua (60.39%; n = 154). The roofs were made of aluminum sheets in Bertoua (85.71%; n = 216) and Santchou (93.05%; n = 241) with the presence of eaves and open ceilings.
Table 2.
Sociodemographic characteristics of households surveyed in Santchou and Bertoua
| Bertoua | Santchou | ||
|---|---|---|---|
| Categories | Characteristics | N (%) | N (%) |
| Gender | Male | 196 (74.8) | 160 (60.8) |
| Female | 66 (25.2) | 103 (39.2) | |
| Education level | Primary level | 45 (18.29) | 43 (16.60) |
| Secondary level | 124 (50.41) | 180 (69.5) | |
| University level | 58 (23.58) | 25 (9.65) | |
| None | 19 (7.72) | 11 (4.24) | |
| People in households | All people | 4.49 (1–14) | 5.97 (1–20) |
| Children < 5 | 0.82 (1–4) | 1.09 (1–5) | |
| Occupation head of household | Small business | 103 (61.67) | 195 (75.88) |
| Civil servant | 36 (21.55) | 52 (20.23) | |
| Housewife | 20 (11.98) | 6 (2.33) | |
| Student | 85 (50.90) | 4 (1.55) | |
| House construction material | Cement blocks | 154 (60.39) | 210 (82.03) |
| Mud and cement | 54 (21.17) | 34 (13.28) | |
| Clay | 13 (5.10) | 12 (4.69) | |
| Plank | 34 (13.33) | 00 (00) | |
| Roof | Tiles/iron sheet | 216 (85.71) | 241 (93.05) |
| Tchated | 27 (10.71) | 17 (6.56) | |
| Other | 9 (3.57) | 1 (0.38) | |
| Eaves | Present Absent |
68 (32.23) 143 (67.77) |
100 (39.37) 154 (60.63) |
| Ceiling | Present | 156 (60.23) | 129 (53.75) |
| Absent | 103 (39.77) | 111 (46.25) |
Percentages do not add up to 100 because these results are from multiple response questions.
N: Total.
Knowledge on the Use of Preventive Measures
More than 90% of respondents from each locality reported being bitten by mosquitoes every night (Table 3). The primary tool used to prevent mosquito bites in both areas was insecticide-treated mosquito nets (96.51% and 93.19% in Santchou and Bertoua, respectively), followed by the spraying of insecticide aerosol bombs (Table 3). Regarding the frequency of insecticide-treated net usage, approximately 68.75% (n = 176) of respondents in Santchou and 55.55% (n = 135) in Bertoua stated that they regularly used mosquito nets (Table 3). Almost all of the mosquito nets available in households in Santchou (94.11%; n = 240) were obtained through mass distribution campaigns (Table 3). In contrast, 28.16% (n = 49) of households in Bertoua mentioned purchasing their nets at the market. The majority of inspected mosquito nets in both locations were less than 6 months old (Table 3).
Table 3.
Population knowledge and attitude concerning malaria prevention and usage of ITNs in Santchou and Bertoua
| Bertoua | Santchou | ||
|---|---|---|---|
| Variables | Answers | N (%) | N (%) |
| Mosquito bites at night | Yes | 247 (96.48) | 242 (92.01) |
| Prevention measures used | Mosquito nets | 245 (93.51) | 253 (96.19) |
| Insecticides Sprays/coils | 55 (20.99) | 91 (34.60) | |
| Screen nets on Windows | 6 (2.29) | 6 (2.28) | |
| Period of use of Mosquito nets | Rainy season | 82 (33.74) | 76 (29.69) |
| Dry season | 26 (10.70) | 5 (1.95) | |
| Regularly | 135 (55.55) | 176 (68.75) | |
| Origin of bed nets used | Freely acquired | 125 (71.84) | 240 (94.11) |
| Bought | 49 (28.16) | 15 (5.89) | |
| Age of bed nets used | <6 mo | 79 (33.76) | 158 (61.71) |
| >6 mo | 78 (33.33) | 37 (14.45) | |
| >1 yr | 31 (13.24) | 32 (12.5) | |
| >2 yr | 46 (19.65) | 29 (11.33) | |
| Reasons for not using mosquito nets regularly | Absence of mosquito nets | 22 (11.96) | 21 (33.87) |
| Heat | 65 (35.33) | 36 (58.06) | |
| Forgetting | 97 (52.72) | 5 (8.06) |
N: Total of respondents.
Ownership and Usage of Insecticide-Treated Nets in Households
The ownership and usage rates of ITNs in households are presented in Table 4. The proportion of households owning at least one ITN was 93.91% in Santchou compared to 60.68% in Bertoua. The proportion of households owning one ITN for every 2 people was 59.31% in Santchou and 50.38% in Bertoua. The proportions of households with access to an ITN varied, ranging from 47.3% in Bertoua to 73.94% in Santchou. The proportions of households that slept under a mosquito net the previous night were 72.70% in Santchou and 41.11% in Bertoua. The usage/access ratios were 0.98 in Santchou and 0.87 in Bertoua, suggesting a high utilization of ITNs in both locations.
Table 4.
Ownership and usage of insecticide-treated nets in households in Kaélé, Tibati, Santchou, and Bertoua
| Sites | % HHs owning ≥ 1 ITN | % HHs owning ≥ 1 ITN for 2 people | % population with access to an ITN within their own HH | % population that used an ITN the previous night | ratio usage: access |
|---|---|---|---|---|---|
| Bertoua | 60.68 | 50.38 | 47.3 | 41.11 | 0.87 |
| Santchou | 93.91 | 59.31 | 73.94 | 72.70 | 0.98 |
HHs, households; ITN, insecticide-treated nets.
Ratio = Usage/Access.
Physical Integrity of Bed Nets in Use
The physical integrity of nets in use in the study sites is presented in Table 5. Following the questionnaire, a total of 768 LLINs, including 336 from Santchou and 432 from Bertoua, were recorded. In Santchou, more than half of these nets were clean (67.56%; n = 227), in good condition (56.85%; n = 191), white in color (85.42%; n = 287) and 43.15% (n = 145) had holes. Most of the respondents reported using water and soap to wash their nets (53.53%; n = 159). The average frequency of washing was 3 times per year. After washing, most respondents reported drying their nets under the sun (53.05%; n = 165). Additionally, holes in the nets were caused by various tensions exerted by the users (100%; n = 145).
Table 5.
General state of LLINs in use in Santchou and Bertoua
| Santchou | Bertoua | ||||
|---|---|---|---|---|---|
| Variables | Observations | N | n (%) | N | n (%) |
| State of the LLINs | Clean | 336 | 227 (67.56) | 432 | 308 (71.30) |
| Dirty | 109 (32.44) | 124 (28.70) | |||
| State | Good | 336 | 191 (56.85) | 432 | 368 (85.19) |
| Damaged | 145 (43.15) | 64 (14.81) | |||
| Color | White | 336 | 287 (85.41) | 432 | 204 (47.22) |
| Blue | 41 (12.20) | 221 (51.16) | |||
| Green | 8 (2.38) | 0 (0) | |||
| Black | 0 (0) | 7 (1.62) | |||
| Holes in LLINs | No | 336 | 191 (56.85) | 432 | 368 (85.19) |
| Yes | 145 (43.15) | 64 (14.81) | |||
| Products used for washing LLINs | Water and soap | 297 | 159 (53.53) | 274 | 123 (44.92) |
| Detergents | 0 (0) | 124 (45.31) | |||
| Just water | 18 (6.06) | 0 (0) | |||
| Bleach | 0 (0) | 2 (0.85) | |||
| Mix | 120 (40.40) | 25 (9.22) | |||
| Places for drying LLINs | Under the Sun | 311 | 165 (53.05) | 259 | 118 (45.55) |
| Shelter | 146 (46.94) | 141 (54.44) | |||
| Causes of the holes | Tensions | 145 | 145 (100) | 64 | 59 (92.19) |
| Harsh washing | 0 | 13 (20.31) | |||
| Fire | 0 | 2 (3.12) | |||
| Other factors | 0 | 9 (14.06) |
Percentages do not add up to 100 because these results are from multiple response questions.
N: Total of nets inspected.
In Bertoua, the majority of LLINs were clean (75.30%; n = 308), in good condition (85.19%; n = 368), were blue in color (51.16%; n = 432), and 14.81% (n = 64) had holes. Most of the respondents reported using water with either detergent (45.31%; n = 124) or soap (44.92%; n = 123) to wash their nets. Products such as bleach (0.85%; n = 2) or a combination of several products were also used (9.22%; n = 25). The nets were washed an average of 3 times per year. After washing, over 50% of the respondents reported drying their nets in the sun (54.44%; n = 141). There were several factors contributing to the holes found on the nets, including stretching tensions (92.19%; n = 59), pressure from washing (20.31%; n = 13), fire (3.12%; n = 2), and other factors.
HI of Nets in Use
Out of the 656 LLINs recorded in Santchou and Bertoua, 370 LLINs were obtained from volunteers for evaluation of the HI. Of the 370 LLINs obtained, 275 LLINs were from Bertoua and 95 LLINs were from Santchou and these LLINs. The relevant data is presented in Table 6.
Table 6.
Categorization of LLINs based on HI and number of holes on bed nets sampled in Santchou and Bertoua
| Characterization | Variables | Santchou | Bertoua |
|---|---|---|---|
| Hole Index | LLINs analyzed | 95 | 275 |
| LLINs with holes (%) | 45 (47.37) | 85 (30.91) | |
| LLINs in good condition (0 < IT < 64) |
20 (21.05) | 46 (54.12) | |
| LLINs damaged (65 < IT < 642) (%) |
5 (5.26) | 25 (29.41) | |
| LLINs not in use (IT > 642) (%) |
20 (21.05) | 14 (16.47) | |
| Number of holes | 1067 | 751 | |
| Type of holes | Number of type I holes (%) | 677 (63.45) | 394 (52.46) |
| Number of type II holes (%) | 189 (17.71) | 147 (19.57) | |
| Number of type III holes (%) | 99 (9.28) | 137 (18.24) | |
| Number of type IV holes (%) | 102 (10.03) | 73 (9.72) |
In Santchou, the LLINs were thoroughly inspected of which majority of the LLINs were Olyset (71%, n = 228); 47.37% (n = 45) had holes and tears. Out of 95 inspected nets, a total of 1067 holes were counted. Type I holes were the most common (677), followed by Type II (189), Type IV (102), and finally Type III holes (99). Approximately 5 (5.26%) of the used LLINs were damaged, and 20 (21.05%) were unusable. However, 20 (21.05%) of the nets with holes were still in good condition.
In Bertoua, 30.91% (n = 85) had holes and tears. Out of 275 inspected nets, a total of 750 holes were counted. Type I holes were also the most common (394), followed by Type II (147), Type 3 (137), and finally Type III holes (73). Approximately 25 (29.41%) of the used LLINs were damaged, and 14 (16.47%) were unusable.
Brands of Sampled Nets in Bertoua and Santchou
Various brands of nets were found in households in Santchou and Bertoua (Fig. 2). These included Olyset, Interceptor, Permanet, Dawanet, Royal Sentry, Magnet, Yorkool, and Olyset plus. The brands Olyset (71.27%; n = 228) and Interceptor (11.60%; n = 37) were frequently found in Santchou. In Bertoua, however, Olyset plus (97.22%; n = 422) was the most common brand.
Fig. 2.
Brand of LLINs used in Santchou and Bertoua.
Bio-efficacy of Distributed Bed Nets in Santchou and Bertoua
The bio-efficacy of LLINs against the major malaria vectors is presented in Table 7. A total of 5,009 An. gambiae s.l. females, including 600 from the susceptible Kisumu strain and 4,409 from the field strain collected in Santchou, were exposed to 44 Olyset brand LLINs. Controls using untreated nets showed knockdown and mortality rates below 3%. Olyset showed minimally efficacy against the tested strains of An. gambiae s.l. The knockdown rate for the susceptible strain was 97.5% (n = 585) and mortality rate 98.16% (n = 589). The field An. gambiae s.l. population was found to display low susceptibility to the LLINs. The knockdown rate was 10.23% (n = 451), and the mortality rate was 14.97% (n = 660).
Table 7.
General effectiveness of LLINs assessed in Santchou and Bertoua
| Sites | LLINs | Species | N tested | nKD60 | %KD 60 (95% CI) | n dead | %Mortality (95% CI) |
|---|---|---|---|---|---|---|---|
| Bertoua | 45 | Kisumu | 4,688 | 4,571 | 97.5 (97.22–97.79) | 4,602 | 98.16 (97.88–98.45) |
| An. gambiae s.l. | 5,194 | 3,246 | 62.49 (62.28–62.71) | 3,181 | 61.24 (61.03–61.45) | ||
| Santchou | 44 | Kisumu | 600 | 585 | 97 (97.22–97.79) | 589 | 98 (97.22–97.79) |
| An. gambiae s.l. | 4,409 | 451 | 10.17 (10–10.36) | 660 | 14.97 (14.83–15.27) |
KD = Knockdown after 60 min; Kisumu: laboratory-sensitive strain; n: number.
A total of 9,882 An. gambiae s.l. females, including 4,688 from the susceptible Kisumu strain and 5,194 from the field strain collected in Bertoua, were exposed to 45 Olyset plus brand LLINs. Controls using untreated nets showed knockdown and mortality rates below 3%. Olyset plus was not effective against the tested field strains of Anopheles gambiae s.l. The knockdown rate for the susceptible strain was 97.5% (n = 4.571), with a mortality rate of 98.16% (n = 4,602). The field strains of An. gambiae s.l. demonstrated low susceptibility to the LLINs. The knockdown rate was 62.49% (n = 3.246), and the mortality rate was 61.24% (n = 3.181).
Overall, the resistance of field strains to LLINs was significantly higher in Santchou compared to Bertoua (χ2 = 962.90; df = 1; P < 0.0001).
Discussion
The assessment of a net’s integrity and bio-efficacy stands as a pivotal aspect in the realm of vector control and disease prevention. The integrity of a net, encompassing its physical durability and resistance to wear and tear, directly influences its ability to provide a protective barrier against disease-carrying vectors. Concurrently, the bio-efficacy of a net, reflecting its capacity to effectively repel or eliminate insects, underscores its functional utility in safeguarding individuals from vector-borne illnesses.
In all research locations, a substantial portion of households possessed at least one mosquito net. However, the prevalence of households having one net for every 2 individuals was noticeably low, consistent with findings in previous studies conducted in Yaoundé and Makenene (Abdou et al. 2019, Djoufounna et al. 2022). It is a common occurrence to witness multiple individuals sharing a room, with some using nets while others do not. This situation can significantly raise the risk of mosquito bites for individuals without net protection.
Several factors were identified as contributors to the underutilization of nets, including discomfort from the heat when sleeping under a net and instances of forgetting to hang the net before bedtime. This situation underscores the need for increased public awareness campaigns to promote adherence to proper net usage practices. Moreover, there were instances where individuals repurposed insecticide-treated nets for agricultural purposes, such as protecting seedbeds in Bertoua and Santchou. These inappropriate practices have been highlighted in previous studies (Abdou et al. 2019; Kala Chouakeu et al. 2021; Ngadjeu et al. 2022) and require heightened attention and intervention.
The physical deterioration of LLINs observed in Santchou and Bertoua could be attributed to the various factors: quality of the nets, environmental conditions, and user behavior. Studies have shown that certain LLIN brands may have better durability compared to others due to their design and manufacturing processes. Furthermore, environmental factors, such as exposure to sunlight, humidity, and temperature fluctuations, can also accelerate the degradation of the nets over time (WHO., 2011). Improper handling and washing practices by users, such as using harsh detergents or washing machines, can contribute to the wear and tear of the nets (WHO, 2013).
Twenty percent of the 95 LLINs in Santchou and 14% of the 275 LLINs in Bertoua were no longer able to effectively serve as a physical barrier due to numerous holes observed in these nets. This rapid deterioration of the mosquito nets less than 2 yr after the start of use could be a result of frequent or poor use of the nets by the population, poor quality of the materials used, repeated washing, exposure to flames, the type of sleeping space covered, and the method of hanging (Mutuku et al. 2013, Lukole et al. 2022). In addition, the mismatch between the configuration of sleeping spaces and the shape of the nets can create tension on the fibers, leading to tears (Nopowo 2020). This highlights the need for regular monitoring of net physical integrity to determine appropriate periods for net redistribution campaigns in order to maximize the impact of treated nets.
The bio-efficacy of LLINs is crucial for their effectiveness in preventing mosquito bites and malaria transmission. The resistance of Anopheles gambiae s.l. populations to insecticides used in LLINs is a growing concern for malaria control. The bio-efficacy tests in Santchou and Bertoua showed very low efficacy of LLINs against the field strains of Anopheles gambiae s.l. Overall, the low mortality of field strains to LLINs was significantly higher in Santchou compared to Bertoua. This result suggests a probable resistance of Anopheles gambiae s.l. populations to the insecticides used in net impregnation. Studies have highlighted the emergence of resistance to pyrethroids, the most commonly used insecticide for net impregnation, in mosquito populations across Africa (Ranson and Lissenden 2016).
This resistance can undermine the ability of LLINs to kill mosquitoes and reduce malaria transmission, highlighting the need for alternative insecticides or vector control strategies (Hemingway et al. 2016). A study conducted by Kala-Chouakeu et al. (2022) in different settings, detected high resistance levels to pyrethroids (Kala-Chouakeu et al. 2022). In fact, the use of pyrethroids against mosquitoes in households can select for resistance within vector populations. Since Santchou and Bertoua are areas where agriculture is intensively practiced, it is likely that the uncontrolled use of pesticide in the cultivation of cash crops, such as cocoa and coffee, could also exert selection pressures (Ngangue-Siewe et al. 2022). However Long Lasting Insecticidal Nets (LLINs) coupled with the synergist piperonyl butoxide have been developed in response to growing pyrethroid resistance. The low knockdown and mortality observed with PBO nets (Olyset Plus) in Bertoua support the influence of different mechanisms in the resistance of mosquito to pyrethroids in this zone (Kala-Chouakeu et al. 2022).
Furthermore, the high mortality rates observed in the susceptible Kisumu strain (>97%) demonstrate the preservation of residual insecticide efficacy by LLINs in both locations. This preservation is likely due to the recent distribution of nets and adherence to maintenance instructions (washing with soap and water, rinsing thoroughly, and drying in the shade). However, most households in the study sites use detergents and bleach to wash the LLINs and dry them under the sun, practices that can deteriorate and reduce the effectiveness of the nets. Previous studies indicated that the repeated use of detergents for LLIN washing can lead to the degradation of the insecticide (Atieli et al. 2010). Similarly, it was also demonstrated that a LLIN that is not regularly washed and is covered in dust, urine, or smoke significantly loses its effectiveness (N’Guessan et al. 2022).
Bed nets commonly encountered during the present survey were Olyset brand in Santchou and Olyset plus brand in Bertoua. These nets are known for their relatively large mesh size and the rigid texture of their fibers (Azizi et al. 2023). These 2 characteristics, combined with poor maintenance practices (washing methods, cleaning products used, etc.), could contribute to the rapid deterioration of LLINs and consequently a loss of their effectiveness.
Conclusion
The aim of this study was to find out whether the level of physical integrity and bio-efficacy of LLINs distributed in Bertoua and Santchou during the 2019 campaign and still in use in these localities remain effective. Based on the study results indicating poor physical integrity and low efficacy of LLINs in Bertoua and Santchou, the NMCP should prioritize immediate actions. They must conduct a thorough assessment of the current LLIN distribution process, emphasizing the need for improved quality control measures to ensure the durability and effectiveness of nets. Additionally, the NMCP should establish a proactive maintenance and replacement strategy for damaged or ineffective LLINs, while also investing in community education initiatives to promote proper net usage. Lastly, research into alternative mosquito control methods and innovative LLIN technologies should be encouraged to enhance malaria prevention efforts in these regions.
Acknowledgements
We are grateful to the authorities and the population of Bertoua and Santchou their good collaborations during the fieldwork. Many thanks to the National Malaria Control Program of Cameroon for providing new nets for substitution.
Contributor Information
Nelly Armanda Kala Chouakeu, Vector Borne Diseases Laboratory of the Research Unit of Biology and Applied Ecology (VBID-RUBAE), Department of Animal Biology, Faculty of Science, University of Dschang, Dschang, Cameroon; Organisation de Coordination pour la Lutte Contre les Endémies en Afrique Centrale (OCEAC), Yaoundé, Cameroon.
Mabu Maxim Bindamu, Organisation de Coordination pour la Lutte Contre les Endémies en Afrique Centrale (OCEAC), Yaoundé, Cameroon; Biochemistry Laboratory, Faculty of Sciences, University of Bamenda, Bamenda, Cameroon.
Idriss Nasser Ngangue Siewe, Organisation de Coordination pour la Lutte Contre les Endémies en Afrique Centrale (OCEAC), Yaoundé, Cameroon.
Leslie Nkahe, Organisation de Coordination pour la Lutte Contre les Endémies en Afrique Centrale (OCEAC), Yaoundé, Cameroon; Laboratory of Parasitology and Ecology, Faculty of Sciences, University of Yaoundé, Yaoundé, Cameroon.
Laura Gilberine Ningahi, Vector Borne Diseases Laboratory of the Research Unit of Biology and Applied Ecology (VBID-RUBAE), Department of Animal Biology, Faculty of Science, University of Dschang, Dschang, Cameroon.
Nina Ghislaine Yensii, Biochemistry Laboratory, Faculty of Sciences, University of Bamenda, Bamenda, Cameroon.
Roland Bamou, Vector Borne Diseases Laboratory of the Research Unit of Biology and Applied Ecology (VBID-RUBAE), Department of Animal Biology, Faculty of Science, University of Dschang, Dschang, Cameroon; Laboratory of Malaria and Vector Research, NIAID, NIH, Rockville, MD, USA.
Parfait Awono-Ambene, Organisation de Coordination pour la Lutte Contre les Endémies en Afrique Centrale (OCEAC), Yaoundé, Cameroon.
Njuabe Theresia Metoh, Biochemistry Laboratory, Faculty of Sciences, University of Bamenda, Bamenda, Cameroon.
Timoléon Tchuinkam, Vector Borne Diseases Laboratory of the Research Unit of Biology and Applied Ecology (VBID-RUBAE), Department of Animal Biology, Faculty of Science, University of Dschang, Dschang, Cameroon.
Christophe Antonio Nkondjio, Organisation de Coordination pour la Lutte Contre les Endémies en Afrique Centrale (OCEAC), Yaoundé, Cameroon.
Author contributions
Nelly Armanda Kala Chouakeu (Conceptualization [equal], Data curation [equal], Formal analysis [equal], Investigation [equal], Methodology [equal], Resources [equal], Software [equal], Visualization [equal], Writing—original draft [equal], Writing—review & editing [equal]), Mabu Maxim Bindamu (Conceptualization [equal], Data curation [equal], Formal analysis [equal], Methodology [equal], Resources [equal], Writing—original draft [equal], Writing—review & editing [equal]), Idriss N. Ngangue-Siewe (Methodology [equal], Writing—original draft [equal], Writing—review & editing [equal]), Leslie diane Nkahe (Formal analysis [equal], Methodology [equal], Writing—original draft [equal], Writing—review & editing [equal]), Laura Gilberine Ningahi (Investigation [equal], Methodology [equal], Writing—original draft [equal], Writing—review & editing [equal]), Nina Ghislaine Yensii (Writing—original draft [equal], Writing—review & editing [equal]), Roland Bamou (Investigation [equal], Methodology [equal], Writing—original draft [equal], Writing—review & editing [equal]), Parfait Awono-Ambene (Project administration [equal], Resources [equal], Supervision [equal], Validation [equal], Visualization [equal], Writing—review & editing [equal]), Njuabe Theresia Metoh (Conceptualization [equal], Resources [equal], Supervision [equal], Validation [equal], Visualization [equal], Writing—review & editing [equal]), Timoléon Tchuinkam (Conceptualization [equal], Investigation [equal], Resources [equal], Supervision [equal], Validation [equal], Visualization [equal], Writing—review & editing [equal]), and Christophe Antonio-Nkondjio (Conceptualization [equal], Funding acquisition [equal], Investigation [equal], Methodology [equal], Project administration [equal], Resources [equal], Software [equal], Supervision [equal], Validation [equal], Visualization [equal], Writing—review & editing [equal])
Funding
This work received financial support from Bill & Melinda Gates and Panafrican Mosquito Association (ID OPP1210340) to CAN.
Conflicts of interest. None declared.
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