Assessing transmission of lymphatic filariasis using mosquitoes in communities with at least five rounds of mass drug administration in Ghana

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There has been a critical question of when to stop Mass Drug Administration (MDA) in lymphatic filariasis (LF) endemic communities. After at least five (5) rounds of MDA with ivermectin and albendazole, it is expected that microfilaraemia should reach a minimum threshold in the human population such that the vectors (predominantly Anopheles gambiae) may not be able to pick up microfilaria during a blood meal. Using Pyrethrum Spray Catches (PSC), mosquitoes were sampled from Ayensuako, Gyaahadze, and Mankrong communities located in Awutu/Senya, Efutu Municipal and Agona East Municipal districts respectively, all in the Central Region of Ghana where more than 5 rounds of MDA had been done. All mosquitoes caught were morphologically identified and dissected for infection with W. bancrofti and the cibarial armature examined for the various species. A total of 550 mosquitoes were collected. Distribution of mosquitoes in these endemic communities was predominantly An. gambiae s.l. – 462/550 (84.0%). The proportion of other mosquitoes species were An. funestus 9/550 (1.6%), An. pharoensis 1/550 (0.2%), Culex sp. 57/550 (10.4%), and Mansonia sp., 21/550 (3.8%). For all samples, microscopy was negative for LF parasites. In Anopheles mosquitoes the cibarial teeth of the Anopheles sp. (average of 15 cibarial teeth (12-19; p = 0.002)) were significantly less than those observed (under the compound microscope) in the Culex sp. (average of 26 cibarial teeth (20-34; p = 0.002)). Although the numbers of mosquitoes collected were low due to the period of collection, the results compared to similar studies in the same region of Ghana indicate that MDA in this area has possibly led to elimination of transmission due to low worm load in the mosquito vectors. There is, however, residual transmission in some of the endemic communities that had participated in at least five rounds of MDA. The impact of this observation and the analysis of the cibarial armature for the different species as discussed shows that elimination in endemic communities would be realized within the stipulated timelines, 2020, if MDA is combined with vector management.
A thesis submitted to the Department of Theoretical and Applied Biology, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree ofmMaster of Philosophy