In the framework of an investigation of distribution of arboviruses in the Federal Republic of Cameroun carried out in 1964 and 1965, attemps were made to isolate arboviruses from mosquitos catured within about 80 km of Yaounde in partially degraded semi-deciduous forest between the dense rain forest and the savana. A total of 192 days capture by net at ground level and 8 night captures on human bait yielded 116 species, subspecies or varieties.
A total of 351 pools was made from the 19,320 females of 46 of the captured species or species-groups; these pools were inoculated into 1 day-old mice for isolation of any arboviruses present. The virus strains were identified by a modification of Casals' methods involving sodium desoxycholate and ether.
Sensitivily testing, and haemaglutination, haemaglutination-inhibition, complement-fixation and neutralization tests.
It proved possible to isolate 13 arbovirus strains, 10 of which have been identifled : 5 of Ntaya or closely related virus, 2 of Middelburg virus, 2 of Bunyamwera virus and 1 of Spondweni virus. One of the unidentified strains was found not to correspond to any of of the African viruses in the collections of the reference centres at Dakar and Entebbe. The other two strains are still undergoing identification.
The most interesting finding is the isolation of 5 strains of, or very closely resembling, Ntaya virus from Culex species; this is the first time that isolation of this virus has been mentioned in the litterature since its original isolation in Uganda, from a pool also consisting mainly of Culex. Middelburg virus, so far isolated from various species of Aedes, was here isolated from a homogeneous pool of Mansonia africana, a species known to be the vector of many other arboviruses. The 2 Bunyanwera virus strains were isolated from Aedes, one of them from a homogeneous pool of the A. domesticus complex: this is the first time that this species-group has been found to be involved in the cycle of an arbovirus. The isolationtion of a Spondweni virus strain from the chrysogaster complex or Erertmapodites adds another member to the already long list of possible vectors of this virus.
During the same period, 634 blood sample; from fever patients were similarly tested by animal inocuIation without revealing any of the above-mentioned viruses. A serological investigation of 193 persons of long residence near the capture sites of the mosquitos showed that these viruses are very rarely found in man, with the possible exception of Bunyamwera virus for which 12% of the sera gave a positive reaction in the haemagglutination inhibition test. This is in line with the finding that none of the other three viruses has yet been shown to cause any human disease. The animal cycle these viruses in the region in question remains to be determined.