00000000Thus, there was an extensive epidemic of DEN-1 in western Senegal at the end of 1979 in the late rainy season and early dry season. Diseases were so mild that this outbreak was unnoticed by the Public Health Authorities. A retrospective study of human and monkey sera collected in the area of eastern Senegal (a zone known for its sylvatic circulation of arboviruses) did not show any trace of DEN-1 virus circulation. It is not known where the virus came from, but, in the absence of a sylvatic circulation, it was thought that the virus could have been introduced through the harbour or the airport of Dakar.

Dengue 2
00000000A single isolate was made in the same village of Bandia in late 1970(36), but the definite identification of the virus only occurred in 1977 and no serological investigation could be carried out. In November 1974 a second isolate was made from a pool of A. luteocephalus caught in a non-human environment in Eastern Senegal(36,37) and a retrospective study of monkeys caught in 1974 - 1975 showed evidence of a small epizootic of DEN-2 in 1974(38). The two strains isolated were obtained following inoculation into suckling mice. From 1979 onwards DEN virus studies became a priority and more sensitive inoculation techniques were introduced, namely inoculation in Toxorhynchites or in insect cell culture.

00000000 In 1981, a large epizootic occurred in Eastern Senegal. Two hundred and thirteen DEN-2 virus strains were isolated from mosquitoes living in jungle areas and one strain was isolated from the blood of a free-living red monkey, Erythrocebus patas(39). Only three species of mosquito gave rise to virus isolates: Aedes (Diceromyia) furcifer (88 strains), Aedes (Diceromyia) taylori (37 Strains) and Aedes (Stegomyin) luteocephalus (87 strains). An additional strain was isolated from a pool of male Aedes taylori. The first isolate was made in the early rainy season in June, and the peak time for isolation occurred in September - October. The epizootic decreased abruptly in November and December, at the beginning of the dry season. The infected monkey was caught in September. The early isolations of June and July (especially that from amel mosquitoes) point to the conclusion that the virus was already present in late 1980. Despite this intense epizootic, three other flaviviruses were also isolated in 1981: Zika, Wesselsbron and Kedougou. A small resurgence of the epizootic was observed in 1982, when a single strain was isolated in September from A. luteocephalus. In November 1981, four pools of potential vectors caught in the neighbouring area of Guinea yielded four virus strains; three from A. africanus and one from A. luteocephalus.

00000000The repercussion in human terms of this epizootic seemed to be very low(38); in January 1983 a retrospective survey was carried out in 13 health centres in the area, but it did not allow evaluation of the degree of human infection, most of the febrile diseases being attributed to malaria. In any case, no trace of DHF or DSS could be found. A single case of DEN-2 infection was observed in a European member of the entomological team; the infection was severe, with a typical rash, and a residual pain in the shoulder joint which persisted for one year. Serological surveillance of children is continuing, and results have indicated that 11 per cent of children were in contact with the virus in 1981. More interesting is the fact that isolated positive responses to DEN-2 antigen were found every year from 1982 to 1985, especially in 1984 when three per cent of the tested sera contained CF antibodies.