Mermithid parasitism of Simulium damnosum s.l. and the transmission of human onchocerciasis

Abstract

Dissection data from a Simulium damnosum s.l. population in northern Ghana, heavily parasitized by the mermithid Isomermis lairdi, are presented. A simple calculation gives reason to suppose that this parasitism may significantly reduce the transmission of onchocerciasis at certain seasons.

An 18S ribosomal DNA barcode for the study of Isomermis lairdi, a parasite of the blackfly Simulium damnosum s.l.

“…Simulium sirbanum and S. damnosum s.s . are also known hosts of I. lairdi (Mondet, 1981; Walsh & Ocran, 1985) . Simulium sirbanum can also be a highly competent host in the field (Walsh & Ocran, 1985), but the situation with S. damnosum s.s .…”

“…Isomermis lairdi Mondet, Poinar & Bernadou parasitizes larvae of the Simulium damnosum Theobald species complex and either prevents them from pupating or kills the adult during its first gonotrophic cycle. Therefore, I. lairdi can have a major impact on the transmission of Onchocerca volvulus (Leuckart) and the spread of human onchocerciasis (Davies et al ., 1984; Walsh & Ocran, 1985). For this reason, it has been argued that insecticide‐based control programmes should take care not to eliminate natural populations of I. lairdi (Davies et al ., 1984; Walsh & Ocran, 1985) and, moreover, that I. lairdi could be used to complement insecticides as part of integrated control strategies (Walsh, 1984).…”

“…Therefore, I. lairdi can have a major impact on the transmission of Onchocerca volvulus (Leuckart) and the spread of human onchocerciasis (Davies et al ., 1984; Walsh & Ocran, 1985). For this reason, it has been argued that insecticide‐based control programmes should take care not to eliminate natural populations of I. lairdi (Davies et al ., 1984; Walsh & Ocran, 1985) and, moreover, that I. lairdi could be used to complement insecticides as part of integrated control strategies (Walsh, 1984). Onchocerciasis control currently focuses on the use of the drug ivermectin and while this has yielded tremendous clinical benefits, treatment has not interrupted transmission (Borsboom et al ., 2003) and there have been reports of possible drug resistance in Ghana (Osei‐Atweneboana et al ., 2007).…”