00000000 Serological studies in monkeys showed results identical to those of the virological study, and from June to December 1981, 27 per cent of monkeys had CF antibodies, often at high titres. In 1982, 33 per cent were positive but at a lower titre, which was attributed to a cumulative effect. Results were entirely negative in 1983 and 1984, but a positive response for IgM using the ELISA test was found in December 1985, showing that the virus was still present in the area.

00000000After this large epizootic, an epidemic was expected in the western part of Senegal, as is usual with yellow fever virus. Despite special surveillance, no epidemic occurred and a single case was diagnosed in a European who travelled in the south of the country in November 1983(40). There is a suspicion that the virus migrated to the West, as yellow fever virus usually does. It is not understood, however, why there has been no epidemic, despite the lack of vaccine.

Dengue 4
00000000DEN-4 virus was first isolated in December 1981 from a patient who had just arrived from the Caribbean Region (Haiti) and who fell ill in Dakar.

00000000 In November 1983, a small epidemic was observed in a European family who lived in Dakar and who did not leave the town in the 14 days before they fell ill. The two children were first infected, but no virological or serological investigations were performed; after about one week, the father and the mother had fever, headache and myalgia, and con of them developed rashes; DEN-4 virus was isolated from both. A third case was serologically diagnosed in Casamance (South-West Senegal). These cases were the first evidence of DEN-4 virus circulation, either in humans or in monkeys.

00000000 More investigations are needed to establish the origin of the virus. The Dakar observations indicate that the virus may have been introduced, but the Casamance case could have originated from a local sylvatic cycle.