Filariasis in Amerindians of Western Guyana with observations on transmission of Mansonella ozzardi by a Similium species of the amazonicum group

ABSTRACT

In order to conduct experimental infection studies on Mansonella ozzardi in local haematophagos Diptera, volunteers infected with this parasite were identified during a microfilaria survey of four Amerindian villages in the Pakaraima Mountains of Western Guyana, near the Brazilian border. M. ozzardi microfilariae were detected in blood smears from 8-21 percent of persons examined. They were also found in skin snips from 8/73 persons all of whom were positive by blood smear examination. No Onchocerca volvulus microfilariae were detected. Dipetalonema perstans infections were found in three of four villages but prevalence rates were only 1-8 percent. Man-baited catches of haematophagous Diptera made at the onset of the dry season in one of the villages yielded only three Simulium species. After the flies were engorged on infected volunteers, M. ozzardi larvae developed to the infective stage in 6-7 days in the most abundant species, a member of the Simulium amazonicum group. Man-biting rates of up to 156 per 15-minute period were recorded for this species in midday collections along riverbanks near one of the villages. Developing filariae, including infective larvae of M. ozzardi, were also found in wild-caught flies. It was concluded that this Simulium species is a vector of M. ozzardi in the study area (Summary)