Presence of Wuchereria bancrofti microfilaremia despite 7 years of annual ivermectin monotherapy mass drug administration for onchocerciasis control: a study in north-west Ethiopia.

BACKGROUND: There is considerable interest in determining whether mass drug administration (MDA) with ivermectin for onchocerciasis control will eliminate coendemic lymphatic filariasis (LF). The objective of this study was to determine the prevalence of LF microfilaremia in onchocerciasis endemic districts that had received 7 years of MDA with ivermectin. METHOD: Three villages with a 2010 LF circulating antigenaemia prevalence (determined in a mapping exercise using immunochromatography tests) ranging from 23 to 56% were surveyed for the presence of Wuchereria bancrofti microfilaria (mf) in 2012. These villages had been treated with ivermectin MDA for onchocerciasis with reported total population coverage of ≥65%. A total of 774 residents aged 2 years and above, of both genders, provided 60 µl nocturnal blood samples between 10 pm and 2 am. Standard thick smears were prepared and examined microscopically after Giemsa staining for the presence of W. bancrofti mf. RESULTS: The mean mf prevalence was 4.7% (village range 1.1-11.0%). The mean mf density was 9.8 mf/60 µl (village range 9-13.1) among the positive individuals. Children in the 2-4-year-old and 5-9-year-old age groups were infected suggesting transmission occurred during the MDA period. A village level review of MDA treatment coverage records showed an average total population coverage of 66.4% over a 7-year period, but with a considerable range of annual coverage (43.0-89.9%). In addition, village level treatment coverage data were missing from the village with the highest mf prevalence (11%) for 2 of the 7 years. CONCLUSION: 7 years of annual mass treatment with ivermectin monotherapy for onchocerciasis did not interrupt LF transmission. In expanding the onchocerciasis ivermectin MDA programme to include LF, albendazole should be added and treatment coverage improved.

Biting behavior and Plasmodium infection rates of Anopheles arabiensis from Sille, Ethiopia.

The man-biting behavior and Plasmodium infection rates of anopheline mosquitoes were investigated in Sille, a hyperendemic malarious area in southern Ethiopia. Seven Anopheles species were identified from all night landing collections, conducted from 18:00 to 06:00h between October 2001 and August 2002. The predominant species was Anopheles arabiensis (55.8%), followed by Anopheles coustani (31.5%), Anopheles pharoensis (9.5%), Anopheles funestus (2.2%), Anopheles nili (0.5%), Anopheles marshallii (0.4%) and Anopheles demeilloni (0.2%). Dissection of A. arabiensis showed an average parous rate of 73.2%. A large proportion of the parous mosquitoes were caught biting in the latter part of the night. Malaria sporozoite rates were determined by ELISA for A. arabiensis, with 0.5% (4/796) infective with Plasmodium falciparum and 1.76% (14/796) with Plasmodium vivax; there were no mixed infections. From our small sample of sporozoite positives we found no association between biting behavior and sporozoite infection status.