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.
Highlights
Lymphatic Filariasis (LF) is a mosquito transmitted parasitic infection that in Africa is caused by Wuchereria bancrofti
Lymphatic filariasis is a mosquito transmitted disease that is best known for causing elephantiasis
We describe a mass drug administration program in central Nigeria that has, since 2000, provided over 23 million cumulative annual treatments to a population of 3.7 million persons
Summary
Lymphatic Filariasis (LF) is a mosquito transmitted parasitic infection that in Africa is caused by Wuchereria bancrofti. LF, which has no animal reservoir, is largely rural and transmitted by Anopheles mosquitoes in West Africa. The adult worms reside in the human lymphatic vessels and cause lymph flow dysfunction that can result in swelling of limbs (lymphedema, elephantiasis) and genital organs (hydrocele), and painful recurrent febrile attacks of acute adenolymphangitis. Microfilariae released by gravid female W. bancrofti worms gain access to the blood stream where they circulate at night and are available for the nocturnally feeding mosquitoes. Microfilariae so ingested pass through three larval molts to reach the L3 stage in about 1–2 weeks; L3 are able to infect humans when infectious mosquitoes return to feed again. The L3 develop to adult male and female worms, where they mate in the human lymphatic system and females produce microfilariae, completing the life cycle of the parasite [1]
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