Table 5.
Details of the studies that carried out both mapping and monitoring
| Study no. | Region | Country | Author& year | No. of districts or villages or sites | Indicator | No examined | Age (years) | Findings |
|---|---|---|---|---|---|---|---|---|
| 1 | South East Asia | Haiti | Drexler et al, 2012139 | Five communes | Ag prevalence | 2639 children | 4-17 | In the study from Haiti (Drexler et al, 2017), the authors have explored if there is active transmission particularly in communities that were identified as low prevalence five communes (during mapping exercise in 2001– Ag prevalence in 6–11-year-olds). A follow-up school surveys for Ag in children were carried out in 2003. For community survey, to examined atleast 100 individuals per community, 20 households within a radius of 5075 m (in urban, peri-urban area) and 100–250 m (rural) of 5–8 index cases (Ag positive children detected in school survey) were selected. Households were selected by systematic sampling method. All individuals available in the selected household was tested for Ag(ICT) and another 200 ul of blood was collected for confirmatory test (using Og4C3). Results of the school survey showed that 2.8% of the 4–17-year-olds were Ag positive. While ICT tested positive children in all five communities. Og4C3 detected Ag positives only in three of the five communities. Analysis on distance from index cases showed that the relationship between Ag positivity and distance from index case was strongest at 20 m and it became weaker with decreasing Ag prevalence with increase in distance. |
| 2 | South East Asia | India | Upadhyayula et al, 2012140 | 120 villages from four districts (Karimnagar, Chittoor, East and West Godavari) | Mf and vector infection prevalence | 23,624 persons | All ages | The study was conducted in the state of Andhra Pradesh in India (Upadhyayula et al, 2012). This study is primarily on spatial mapping and analysis of LF over a 3-year period from 2004 to 2007, during which the MDA was implemented.Blood samples were collected from individuals and data on entomology and socio-economical aspects were collected. Mf prevalence in these districts was 31.5% (with the least being 8.9%) and the disease rate ranged between 0.5% and 2.3%. All the villages were geo-referenced with way points, and these were used to create maps on filariasis at village level. While both east and west Godavari districts were hyper endemic, Karim Nagar and Chittoor fell under medium endemicity. The spatial mapping showed various levels of infection even after implementation of MDA |
| 3 | Africa | Tanzania | Simonsen et al, 2014141 | Seven districts of Tanga region | Mf and Ag prevalence | 2753 persons for Ag 555 persons for Mf 1700 mosquitoes |
All ages | The study describes the LF control started in rural areas of Tanga region of Tanzania in 2004 completing 8 rounds currently. Levels of transmission and human infection decreased initially, and became less pronounced in subsequent years. Even after 6 MDAs transmission was on-going at a reduced level. Seven other districts in the Tanga region (total 8 districts) were included for monitoring in 2013. Spot check community and school based were conducted in Tanga district. Four hamlets of Kirare village were for the community study and standard I pupils (6–7-year-olds) were examined for Ag (ICT) every year. In other districts, two villages were purposively selected from each district. A total of 200 6–7-year-olds were screened for Ag during 2013. Those positive for Ag only were bled for Mf smears. Vector surveillance was done using light traps in 50 selected households of Kirare village. Mapping was done by using the geo-coordinates of the sites and kriging was used to estimate prevalence in regions that were not surveyed. Results from Tanga district surveys indicate that both Mf and Ag prevalences reduced compared to baseline levels. Prevalence of chronic filarial manifestations (hydrocele/elephantiasis) was less than half of that in 2004. Dissection of msoquitoes post MDA 7 and eight rounds showed no filarial infections. Ag prevalence in 6-7yo since the start of MDA had a declining trend and after the 8th round, the prevalence was 2.3% (91% reduction compared to pre-MDA level of 25%). The authors conclude that though there is a positive downward trend in LF transmission and human infection, LF is still widespread in many parts of the Tanga region even after eight rounds of MDA, particularly in coastal areas. Lower infection rates in inland districts suggests that MDA could be stepped down after rigorous assessment so that resources could be diverted to upscale control activities in coastal districts. |
| 4 | Western Pacific | American Samoa | Lau et al, 2014142 | Three islands | Ag and Ab prevalence | 555 persons | All ages | In this study (Lau et al, 2014), the success story of MDA for 5 years (2000–2006) following which the MDA was stopped (based on TAS) and the post MDA surveillance thereafter is described in detail. The LF antigen (Og4C3) and antibody (Wb123 and Bm14) tests were performed on the adult serum samples (n=807) from a serum bank where the samples were collected for a study on leptospirosis, 4 years after the last effective round of MDA. Information on the residence of the participant whose serum was used was used to look into geographical clustering of serologically positive cases. Results showed that which Ag prevalence was 0.75%, antibody prevalences were 8.1% for Wb123 an 17.9% for Bm14. Antigen and antibody prevalences were inversely associated with number of years of living in American Samoa. While antigen prevalence showed spatial variation, antibody prevalence did not show any spatial pattern. Higher prevalence of antigen in adults shows that residual infection is still there in the communities. Further, migrants (from neighbour LF endemic areas) showed higher antigen prevalences. Authors suggest that TAS may not be able to detect transmission hotspots. In the discussion the authors suggest that the risk of LF and drivers of transmission are likely to be heterogeneous within any evaluation units, and could be influenced by many factors such as climatic conditions, population density, urban versus rural areas, MDA coverage, and vector species and density. Therefore the average prevalence in an evaluation unit could mask focal areas of high prevalence (hotspots) if they are surrounded by large areas of low prevalence. Hotspots are more likely to be missed if they are small, in evaluation areas with greater spatial heterogeneity, and when prevalence is very low such as in the post-MDA surveillance phase. |
| 5 | Western Pacific | Papua New Guinea | Graves et al, 2013143 | 324 survey sites between 1980 and 2011 in 80 districts | Mf and Ag prevalence | 37,425 persons for MF 43,264 persons for ICT 16,221 persons for Og4c3 |
All ages | This study is a review in which the LF elimination programme in Papua New Guinea at district level since 1980 to 2011, ie pre and during MDA. Data from a total of 312 district level surveys were utilized for this study. Data on Mf and Ag(ICT and Og4C3) were collected. Results indicate that, on combining these data, the estimates for Mf, ICT and Og4C3 when crudely averaged over districtswere 18.5% for Mf, 10.1% for ICT and 45.5% for Og4C3. Comparison in terms of diagnostic methods showed that Mf prevalence was always lower than ICT prevalence in most surveys. Only one survey reported higher Mf prevalence than that of Ag prevalence (using Og4C3). With respect to time period over every 10 years, it was seen that there was a decline in Mf and Og4C3 prevalences. However no obvious decline was observed in Ag prevalence based on ICT. Results indicated that there was large variation in LF prevalence in the country which may be related to the diverse altitude, geographical and ecological factors and also to the mosquito vectors in different regions of the country. Further, the heterogeneity could be due to the previous malaria control activities and recent distribution of insecticide mosquito nets and to some extent the MDA for LF in limited sites. It was also shown that the number of LF endemic districts differed with GPELF criteria specified earlier and the modified forms. While the earlier criteria classified 60 endemic districts, the modified gave only 36 endemic districts. The alternative criteria defining endemic districts as that one with ≥1% Ag prevalence classified only 34 as endemic districts. On the whole, based on these criteria, about 20 districts do not require MDA as per GPELF criteria 1 and 2. At the outset this review highlights the gaps in data and the knowledge on the remaining unknown districts. |
Abbreviations: LF, Lymphatic filariasis; DEC, Diethylcarbamazine; IVM, Ivermectin; Ag, Antigeneamia; Mf, Microfilaraemia; Ab, Antibody; MDA, Mass drug administration; TAS, Transmission Assessment Survey; ICT, Immunochromatographic Test; MX, Molecular Xenomontoring.