Transmission ofOnchocerca volvulus, O. ochengiand type D filariae bySimulium damnosums.l. in north Cameroon and its influence on the epidemiology of human onchocerciasis

Abstract

mainly investigated, although other parts of the country were visited to a lesser extent. Onchocerciasis was found only in villages along the former two rivers. No infected individuals were recorded from 987 people sampled at thirty-five localities in the regions of Cacheu, Oio and Tombali outside the known foci. Of 516 people examined in six villages along the Geba river 102 (19 %) were infected with the disease. The data show that the disease was more prevalent in the older age groups. Skin densities were relatively low with the majority of infected individuals having less than 15 mff/mg. Investigations in villages along the Corubal river showed that 316 (37 %) of 833 individuals examined were infected. An analysis of the disease in relation to age and sex shows that although larger numbers of older people were infected the disease was also significant in younger males. Skin densities were also higher than for individuals from villages along the Geba river. Typical symptoms of onchocerciasis were seen in infected individuals and 48 of the infected people were blind (31 males and 17 females). In most cases this was due to the presence of microfilariae in the eye. The data presented indicate that the more important of the two foci is that of the Corubal river. Irrigation schemes along the upper reaches of the Geba river have drastically reduced water flow and transmission is believed to be only sporadic or even absent because of the paucity of S. damnosum s.l. in this area.

Individual exposure to Simulium bites and intensity of Onchocerca volvulus infection

“…Results from three days of observation per "test-person". 1 : Clothing (estimate degree of protection; from [4]): lss - long sleeved shirt (5%); sss - short sleeved shirt (0%); lt - long trousers (30%); sh - shoes (30%); so - socks (30%); sk - skirt (20%); 2 : Standard ABR and ATP, measured by the fly-collector at the river banc; data from [6] and [7]. …”

“…Since we did not dissect the flies we caught, we were not able to determine the DTP from our data, thus we used the data from [6] and from [7]. Here we present the results from a small survey conducted in the rainforest and the savannah of Cameroon.…”

Onchocerca ochengitransmission dynamics and the correlation ofO. ochengimicrofilaria density in cattle with the transmission potential

“…The higher infection of the flies with O. ochengi as compared to O. volvulus may be due to the fact that most of the cattle carry O. ochengi infections as described earlier by Wahl et al [27], providing the more accessible and main source of blood meals for the vectors. Low O. volvulus infection rates (17%) in humans in the locality [28] may also be a contributing factor to the low transmission rates of human onchocerciasis. In this area, the flies will have a low human reservoir pool (O. volvulus) from which to draw infections while a large reservoir of cattle (O. ochengi) parasites is readily available.…”

Vector competence of the Simulium damnosum complex in Cameroon for Onchocerca spp. from cattle

“…In some parts of northern Cameroon the high proportion of 0.ochengi L3 in man-biting S.damnosum s.1. apparently protects the local population from severe onchocerciasis, by inducing partial cross-immunization against 0. volvulus (Wahl et al, 1994b).…”