Burkina Faso (formerly Upper Volta)

00000000During a longitudinal survey of fever virus circulation in different wooded areas of the eastern part of Upper Volta, a total of 68 strains of DEN-2 virus were isolated between September and November 1980, at the end of the rainy season and the beginning of the dry season(32,33). The main mosquito involved was Aedes (Stegomyia) luteocphalus, from which 65 strains were isolated, followed by Adeds (Stegomyia) africanus, which gave rise to two strains of DEN-2. Aedes (Aedimorphus) cumminsi gave rise to one strain of DEN-2, but this isolate was not thought to necessarily signify that this species of Aedes is an efficient vector. No significant differences were observed in the infection rates of A. luteocephalus during the three months of the survey, but significant differences were noticed according to the type of wooded area.

00000000 No serological data are available for this epizootic, but, bearing in mind the possible role of unknown vertebrates, it is likely that monkeys and probably humans played the main role as vertebrate hosts.

00000000 After this epizootic, one strain of DEN-2 virus was isolated from A. aegypti caught in the town of Bobo-Dioulasso and there was one case of disease in an expatriate which was serologically confirmed. At the same time, an epidemic occurred in the town of Ouagadougou, where 29 expatriates and one African showed an intense dengue syndrome(34). DEN-2 virus was isolated from six cases, and serological investigation produced evidence for the dengue origin of the disease in 21 cases. Only two cases were children. No DHF or DSS were recorded, but there were slight haemorrhagic cutaneous symptoms in four cases. This epidemic occurred between September and December, in the late rainy season and early dry season. Seasonal epidemics of dengue-like fever were noticed for at least five consecutive years in Ouagadougou, but DEN virus was isolated only in 1982. In 1983, no DEN isolate was obtained from febrile patients.

Ivory Coast

00000000 As in Upper Volta, an important sylvatic circulation of DEN-2 virus was found in 1980 in the sub-Sudanese savannahs(33,35). Twenty-eight strains were isolated from wild vectors: Aedes (Diceromyia) furcifertaylori group (17 strains), Aedes (Stegomyia) luteocephalus (seven strains), Aedes (Stegomyis) opok (three strains) and Aedes (Stegomyia) africanus (one strain); one strain originated from wild caught males of the Aedes furcifertaylori group. The first isolate was made in May, after about one month of the rainy season, and the last was made in October in the late rainy season.

00000000 A serological carried out in humans in the same area one year later showed that HI antibodies were present for one or severa Flavivirus antigens, but that the dengue antibodies were always at a very low titre(33). For this reason it was thought that monkeys were the main vertebrate hosts involved in the transmission.

00000000 A single human case of DEN-2 infection was diagnosed in the town of Abidjan in 1982, two years after the epizootic.