YELLOW-FEVER, DENGUE-2 AND OTHER MOSQUITO -BORNE ARBOVIRUSES, IN BURKINA-FASO, FROM 1983 TO 1986 - ENTOMOLOGICAL AND EPIDEMIOLOGIC ASPECTS

An arbovirus surveillance was carried out in Burkina Faso from 1983 to 1986. It was based on crepuscular catches of mosquitoes on human bait in some wooded areas and in one town. The total collection was 228 ca tches with an average of 8 men per catch. The total number of mosquito es caught was 44,956 among which 32,010 potential vector of yellow fev er; all these mosquitoes were analysed for arbovirology. In the south- western part of the country (region of Bobo-Dioulasso), surveillance w as conducted each year from August to November, whilst the circulation of Aedes-borne arboviruses is well known to be favoured. In 1983, 198 4 and 1986, seven strains of yellow fever virus were isolated in circu mstances remarkably similar. They came from selvatic areas and never f rom the town. They concerned only Aedes (Stegomyia) luteocephalus whic h is the very predominant potential vector of yellow fever in the regi on. They were obtained in low figure, between 1 and 4 per year. They o ccurred from 27th of October to 21th of November. These observations c onfirm that the southern portion of the Sudan savanna zone of West Afr ica is the setting of a customary circulation of yellow fever virus an d therefore belongs to the endemic emergence zone. In 1986, two strain s of dengue 2 virus were isolated. One concerned Ae. luteocephalus fro m the selvatic area, the other Ae. (St.) aegypti from the heart of tow n. These data suggest two distinct cycles for dengue 2 virus, one urba n and one selvatic, which could coexist simultaneously in the same reg ion. In the south-eastern part of the country (region of Fada-N'Gourma ) a yellow fever epidemic occurred between September and December 1983 ; its study has enable to precise their entomological aspects. The ent omological inoculation rate of yellow fever virus has been evaluated t o 22 infected bites per man during the month of october, for a man liv ing close to forest gallery. 25 strains of yellow fever virus strains was isolated from Ae. (Diceromyia) furcifer which is the potential vec tor the most abundant in this region: the main role of this species in an epidemic was confirmed. An investigation in September 1984 had not permitted isolation of the virus therefore it is suspected that the l arge epizootic circulation of virus in 1983 has not been renewed the y ear after. In total 59 viral strains belonging to 10 different viruses were isolated from 9 species of mosquitoes. Two strains of Rift Valle y fever were isolated from Ae. furcifer and Ae. (Aedimorphus) cumminsi in the south-eastern part of the country.