Evaluating The Prevalence And Transmission Of Lymphatic Filariasis In Two Rural Communities In The Western Region After Ten Rounds Of Mass Drug Administration

ABSTRACT

Control of lymphatic filariasis (LF) in Ghana is based on annual mass drug administration (MDA) with a combination of ivermectin and albendazole, in order to halt transmission. It is expected that 5-6 rounds of MDA should result in the interruption of transmission. This research present findings from a study in two endemic rural communities in Western Ghana, after ten rounds of MDA. The study was conducted in Agona Princess and Akonu in the Ahanta West District and Nzema East Municipality respectively. Both Districts commenced MDA in 2000 and 2001 respectively.

The effect of treatment on human infection and mosquito transmission was monitored in the communities from December 2014 to June 2015. The screening tool used in this study was CFA-testing with ICT cards followed by examination of only CFA positive individuals for mf using the counting chamber (CC) and thick blood smear (TS) techniques. Mosquitoes were also sampled using the pyrethrum spray collections (PSC) and investigated for Wuchereria bancrofti infection using dissection and molecular analysis.

During the December parasitological survey, 370 subjects were examined. 13% were positive for circulating filarial antigens (CFA). The CC and TS detected 4% of the population with microfilariae (mf) in the blood, with an intensity range of 1-226 mf/ml and 1-50 mf/ml respectively. Three months (March, 2015) after treatment of individuals with W. bancrofti infections, the parasitological indices decreased considerably to 5% ( for CFA), 1% (CC) and 0.3% (TS) with respective mf intensity range of 1-11 mf/ml (CC) and 1 mf/ml (TS). The June 2015 parasitological survey revealed an increase in antigenaemia prevalence (7.6%) while the mf prevalence remained considerably the same. In assessing transmission indices, out of the 132

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mosquitoes collected, 125 (94.7%) were Anopheles gambiae s.l. Molecular studies identified all anophelines as An. melas. One An. melas was found infected with three L2s of W. bancrofti, which was confirmed by PCR analysis. There was no recovery of infective stage larva of W. bancrofti in the mosquito samples.

In this study, a decline in mf prevalence and intensity was observed after treatment. However, the remaining positive individuals represent a reservoir for the continued transmission of the disease. This calls for the need for bi-annual treatments instead of the current once-a-year treatment. Further, questions have been raised about the possible development of drug resistance following several years of treatment. A continued monitoring for parasite repopulation rates and drug resistance markers would help establish the basis for resistance to ivermectin and albendozole in the study areas.