Studies of the transmission of Onchocerca volvulus by species of the Simulium damnosum complex occurring in Liberia
Zeitschrift für Angewandte Zoologie 70(1): 101-117
ISSN/ISBN: 0044-2291 Accession: 001128316
The transmission of O. volvulus by species of the S. damnosum complex was studied throughout yearly cycles in different vegetation zones of Liberia. Annual biting rates (ABR) and annual transmission potentials (ATP) ranged from 1000-280,000 bites of S. damnosum s.l. and 16-5,000 infective larvae of O. volvulus/man per yr. ATP of > 2000 were associated with high endemicity of onchocerciasis in the human population. A reduced vectorial capacity due to low parous rates and zoophily was observed in fly populations on the St. Paul River where S. sanctipauli has its breeding sites. Normal development of O. volvulus to the infective stage was observed in flies from this area when they had been fed on microfilaria carriers during the rainy season; when parous rates were lowest and little natural transmission took place. A close man-fly contact and intense transmission was established by fly populations in the vicinity of smaller streams, the breeding site for S. yahense. Identification of alcohol preserved flies revealed that S. sanctipauli and S. yahense were the main components of the biting populations in most parts of Liberia; S. damnosum s.s. was also caught at a few sites, S. sanctipauli and S. yahense should be considered as the most important vectors of onchocerciasis in Liberia.