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

FPIDFMIOLOGY OF FILARIASISmainly 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.SIMULIIDAE '"TPhe distribution of Simuliidae in Guinea Bissau was inves-I tigated (Gracio et al., in press) and identification of the cytospecies of the Simulium damnosum complex made at localities within and adjacent to the Corubal focus (Charalambous et al., in press).Only S. sirbanum and S. konkourense were found along the Corubal river between March 1990 and November 1992.The former species predominated at localities along the upper reaches and the largely zoophilic S. konkourense was the main cytoform along the lower reaches of the river.Morphometric analysis of cytotyped larvae showed these two cytotaxa of S. damnosum could be separated using the number of rows of hooks in the posterior circlet and the number of hypstomial setae.Unfortunately, this differentiation of the two cytotypes contained a large percentage of overlap so that unequivocal identifications could only be made for specimens in the extremes of the combined range (Lowry et al., in prep.).Entomological surveys showed the presence of the following simuliid species associated with the Geba and Corubal river basins : Simulium alcocki, S. gartnsi, S. djallonense, S. cervicornutum, S. unicornutum, S. ruficorne, S. adersi, S. tridens and S. hargreavesi.pare filarial development in the two cytospecies.Insufficient numbers of S. konkourense precluded the completion of the experiment.