Individual exposure to Simulium bites and intensity of Onchocerca volvulus infection

C A Jacobi,P Enyong,A Renz

doi:10.1186/1756-3305-3-53

Abstract

BackgroundOnchocerca volvulus, the causative agent of river blindness, is transmitted through the black fly Simulium damnosum s.l., which breeds in turbulent river waters. To date, the number of flies attacking humans has only been determined by standard fly collectors near the river or the village. In our study, we counted the actual number of attacking and successfully feeding S. damnosum s.l. flies landing on individual villagers during their routine day-time activities in two villages of the Sudan-savannah and rainforest of Cameroon. We compared these numbers to the number of flies caught by a standard vector-collector, one positioned near the particular villager during his/her daily activity and the other sitting at the nearest Simulium breeding site.ResultsUsing these data obtained by the two vector-collectors, we were able to calculate the Actual Index of Exposure (AIE). While the AIE in the savannah was on average 6,3%, it was 34% in the rainforest. The Effective Annual Transmission Potential (EATP) for individual villagers was about 20 fold higher in the rainforest compared to the savannah.ConclusionsHere we show for the first time that it is possible to determine the EATP. Further studies with more subjects are needed in the future. These data are important for the development of future treatment strategies.

Highlights

Onchocerca volvulus, the causative agent of river blindness, is transmitted through the black fly Simulium damnosum s.l., which breeds in turbulent river waters
Existing data are based on an assessment of daily biting rate (DBR) and daily transmission potential (DTP) that probably overestimates the values as they are based on the standard vector collector
A more realistic estimate of the effective DBR and DTP can be obtained by catching flies at different localities around and in the villages, where the villagers spend most of the day-time, and by measuring the Daily Visiting Frequency and exposure of different age and sex groups [4,10]

Summary

Introduction

Onchocerca volvulus, the causative agent of river blindness, is transmitted through the black fly Simulium damnosum s.l., which breeds in turbulent river waters. We counted the actual number of attacking and successfully feeding S. damnosum s.l. flies landing on individual villagers during their routine day-time activities in two villages of the Sudan-savannah and rainforest of Cameroon We compared these numbers to the number of flies caught by a standard vector-collector, one positioned near the particular villager during his/her daily activity and the other sitting at the nearest Simulium breeding site. The intensity of transmission is commonly assessed using standardized procedures with a standard fly collector, catching all simuliid female flies which come to feed on his fully exposed legs [1,2,3,4]

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