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. 2011 Oct;5(10):e1346.
doi: 10.1371/journal.pntd.0001346. Epub 2011 Oct 11.

Epidemiological and entomological evaluations after six years or more of mass drug administration for lymphatic filariasis elimination in Nigeria

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Epidemiological and entomological evaluations after six years or more of mass drug administration for lymphatic filariasis elimination in Nigeria

Frank O Richards et al. PLoS Negl Trop Dis. 2011 Oct.

Abstract

The current strategy for interrupting transmission of lymphatic filariasis (LF) is annual mass drug administration (MDA), at good coverage, for 6 or more years. We describe our programmatic experience delivering the MDA combination of ivermectin and albendazole in Plateau and Nasarawa states in central Nigeria, where LF is caused by anopheline transmitted Wuchereria bancrofti. Baseline LF mapping using rapid blood antigen detection tests showed mean local government area (LGA) prevalence of 23% (range 4-62%). MDA was launched in 2000 and by 2003 had been scaled up to full geographic coverage in all 30 LGAs in the two states; over 26 million cumulative directly observed treatments were provided by community drug distributors over the intervention period. Reported treatment coverage for each round was ≥85% of the treatment eligible population of 3.7 million, although a population-based coverage survey in 2003 showed lower coverage (72.2%; 95% CI 65.5-79.0%). To determine impact on transmission, we monitored three LF infection parameters (microfilaremia, antigenemia, and mosquito infection) in 10 sentinel villages (SVs) serially. The last monitoring was done in 2009, when SVs had been treated for 7-10 years. Microfilaremia in 2009 decreased by 83% from baseline (from 4.9% to 0.8%); antigenemia by 67% (from 21.6% to 7.2%); mosquito infection rate (all larval stages) by 86% (from 3.1% to 0.4%); and mosquito infectivity rate (L3 stages) by 76% (from 1.3% to 0.3%). All changes were statistically significant. Results suggest that LF transmission has been interrupted in 5 of the 10 SVs, based on 2009 finding of microfilaremia ≥1% and/or L3 stages in mosquitoes. Four of the five SVs where transmission persists had baseline antigenemia prevalence of >25%. Longer or additional interventions (e.g., more frequent MDA treatments, insecticidal bed nets) should be considered for 'hot spots' where transmission is ongoing.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Plateau and Nasarawa States, Nigeria: Baseline LGA LF Antigen prevalence and sentinel village locations.
Surveys in 70 villages sampled 6,489 adults for LF antigen in 1999 and 2000 (50–100 adult residents of each village) located in the 30 LGAs comprising Plateau and Nasarawa states. The map is color coded based on the mean antigen results (mean of the village means): shown in red are ten LGAs having a mean baseline antigen prevalence exceeding 25% that form a middle band stretching from southwest to northeast.
Figure 2
Figure 2. Scaling up onchocerciasis and lymphatic filariasis treatments: 1992–2009.
Light bars show ivermectin monotherapy for onchocerciasis MDA provided in rural villages in 12 LGAs deemed onchocerciasis endemic in 1992. Dark bars show LF treatment with ivermectin and albendazole combination therapy. Arrows indicate LF scale-up phases. Phase 1: pilot studies completed in two onchocerciasis endemic LGAs (Pankshin in Plateau state and Akwanga in Nasarawa state). Phase 2: LF MDA expanded to the remaining 10 onchocerciasis endemic LGAs, to now include large towns in those LGAs that had previously been untreated under the onchocerciasis program. MDA in Phases 1 and 2 was for both onchocerciasis control and LF elimination. Phase 3: LF MDA expanded to all but four of the non-onchocerciasis endemic LGAs. Phase 4: LF MDA reached full geographic coverage (all 30 LGAs) and the capital cities of Jos (Plateau) and Lafia (Nasarawa). MDA added in Phases 3 and 4 were only for the purpose of LF elimination.
Figure 3
Figure 3. Reported village treatment coverage (eligible population): 2004 and 2009.
This x axis shows reported village level treatment coverage ranges based on community CDD registers, and the y axis shows the percent of villages that reported coverages falling into that treatment coverage range for the years 2004 and 2009. Forty-nine percent of 3677 villages reported over 85% coverage of the eligible population in 2006, while 73% of 3638 villages reached that goal in 2009.
Figure 4
Figure 4. Mean sentinel village microfilaremia prevalence by MDA treatment year (n = 10,753).
Nocturnal microfilaremia as determined by 60 ul thick smear. SV results across all four MDA phases have been adjusted to MDA treatment year for comparability. No pretreatment data are available for Gbuwhen, Gwamlar, Lankan, Maiganga and Seri, so earliest available mf data point was used as the baseline figure. Bars show 95% confidence intervals. Chi square for trend for all years was significant (p = 0.035), but was not significant using an analysis between baseline and MDA year 6 (p = 0.187). In addition, the key threshold of <1% microfilaremia was not attained by MDA year 6.
Figure 5
Figure 5. Mean sentinel village antigen prevalence by MDA treatment year (n = 9,394).
Filarial antigenemia as determined by ICT testing. SV results across all four MDA phases have been adjusted to MDA treatment year for comparability. Data for the baseline antigen for five villages (Gbuwhen, Gwamlar, Lankan, Maiganga, and Seri) were from 1999–2000 mapping surveys. Baseline for the remaining villages (Akwete, Anzara, Babale, Dokan Tofa, Piapung) combined values from the community wide nocturnal pre-treatment surveys conducted in 2003 with pre-treatment data from the 1999–2000 mapping surveys. Chi square for trend not significant (p = 0.06 for all MDA years and p = 0.271 for baseline through MDA year 6). Bars show 95% confidence intervals.
Figure 6
Figure 6. Mean mosquito infection (all larval stages) by MDA treatment year in 10 sentinel villages (n = 44,668).
Dissections from bimonthly intradomiciliary pyrethrum knockdown collected mosquitos for all larval stages (L1–3) combined across all SVs and adjusted to MDA treatment year for comparability. Baseline mosquito infection rates are the aggregate values from pretreatment and the first two years of treatment; no baseline data were available for Babale SV. Chi square for trend for all years was highly significant (p = 0.008), but the trend analysis was not significant using data between baseline and MDA year 6 (p = 0.131). Bars show 95% confidence intervals.
Figure 7
Figure 7. Age-specific prevalence for mf or LF antigen in Dokan Tofa and Piapung sentinel villages.
Panel A: Dokan Tofa pretreatment prevalence by age group (n = 418). Panel B: Piapung pretreatment prevalence by age group (n = 400). Panel C: Dokan Tofa prevalence by age group after 6 rounds of MDA (n = 223). Panel D: Piapung prevalence by age group after 6 rounds of MDA (n = 280). Boxes show numbers sampled in each age group. Pretreatment sample for mf is different from Table 2 because ages were not available on all persons tested. Pretreatment sample for antigen for these SVs are different than baseline figure shown in Table 3 because 1999/2000 mapping data were added to baseline calculation in Table 3 (see Methods).

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