The status of Simulium oyapockense and S.limbatum as vectors of human onchocerciasis in Brazilian Amazonia

Abstract

In an attempt to explain the current distribution of onchocerciasis in the forests of northern Brazil (Moraes et al., 1979, 1986), and its potential for dispersal to other areas, this study compares the vector status of Simulium oyapockense Floch and Abonnenc, 1946 in both a hypoendemic and an onchocerciasis free area with that of S. limbatum Knab, 1915 in the latter area. Both species allowed the full development of Onchocerca volvulus (Leuckart) to the infective L3 stage after experimental infection with microfilariae. Their vector competence was significantly lower than for other efficient vector species in South America and Africa because of the lethal effect of the cibarial armature on ingested microfilariae. The low vector capacity of S. oyapockense, together with the low prevalence and intensity of infection of O. volvulus, probably explains why onchocerciasis has not significantly increased in intensity over the last 10 years in the hypoendemic part of the Amazonian focus. Omnipresence of both vector species in the adjacent savanna region, however, could facilitate the spread of onchocerciasis if human population movements continue from the hyperendemic part of the onchocerciasis focus.

Simuliid blackflies (Diptera: Simuliidae) and ceratopogonid midges (Diptera: Ceratopogonidae) as vectors of Mansonella ozzardi (Nematoda: Onchocercidae) in northern Argentina

“…C. insinuatus was a less efficient host to this filaria in Colombia (Tidwell & Tidwell 1982), while Lowrie and Raccurt (1981) and Raccurt and Lowrie (1981) Yarzábal et al (1985), which were all more effective hosts in terms of these parameters. It has been shown by Shelley et al (1987) that S. oyapockense s.l. in the Brazilian Amazon is a relatively poor host to O. volvulus because of the damage caused by its cibarial teeth to microfilariae during ingestion, and that this was a major factor in determining vectorial competence in vector simuliid species in Latin America (Shelley 1988(Shelley , 1994.…”

Human Onchocerciasis in the Amazonian Area of Southern Venezuela: Spatial and Temporal Variations in Biting and Parity Rates of Black Fly (Diptera: Simuliidae) Vectors

“…is a very efÞcient vector of Onchocerca volvulus Leuckart, whereas in the lowlands S. oyapockense Floch & Abonnenc s.l. plays a lesser role (Shelley et al 1987;Basáñ ez et al 1988Basáñ ez et al , 1995. Recently, onchocerciasis prevalence has been demonstrated to increase with altitude along two ßuvial systems of the Amazonian area (Vivas-Martṍnez et al 1998), conÞrming previous observations (Rassi et al 1977, Yarzábal et al 1983).…”

Blackflies (Diptera: Simuliidae) of Southern Guyana with keys for the identification of adults and pupae: a review

“…Preliminary studies on its man-biting densities and insecticide trials with temephos have been reported (Humphrys et al 1977, Rambajan 1981. Shelley et al (1987) showed that this species is capable of acting as a host to Onchocerca volvulus outside the Amazonia onchocerciasis focus in Brazil and hence it may be a vector of M. ozzardi in Guyana.…”