During the end of the rainy season, from October to November 1983, the south eastern part of Upper Volta experienced a major epidemic of yellow fever. The outbreak occurred in an area of undifferentiared savannah of the dry rype, cattle raising area where large numbers of Peulh nomads have settled over the past ten years. The outbreak especially affected people living along forest galleries.
Bload samples and liver specimens from patients and pools of mosquitoes were collected. 5 strains of yellow fever virus obtained from 17 blood samples and 11 strains from 13 liver specImens. The virus isolations were made by inoculatlon into suckling mice. Aedes pseudoscutellaris (Mos 61) cells, and Toxorhynchites brevipalpis. 1 strain of Crimean Congot haemorrhaglc fever (CCHF) virus was also isolated from blood, by inoculatlon into suckling mice. The virus was not isolated ln cell culturcs or in Toxorhynchites. The virus was identified by complement fixation and neutralisation tests. The CCHF virus was isolated from the blood of a patient who presented with haemorrhagic syndrom and jaundice at first diagnosed as yellow fever. The patient survived. A serological survey in the patient's village picked up only 1serum among 42 that was positive for complement-fixing antibodies (titre 4) to the CCHF antigen This serum was negative by indirect immunofluorescence (IFA). In contrast, 28 of the 42 sera possessed complement-fixing antibodies (titres 8 to 256) against the yellow fever antigen. The only other case of CCHF virus Infection with haemorrhagic syndrome we know of from West Africa was in Mauritania (J. F. S., P Aubrey, McCormicK, J P.D., unpublished).
Fom 120 sylvatlc mosquito pools, 2 strains of Rift Valley fever(RVF) virus were isolated from a pool of 17 females Aedes (Aedimorphus) cumminsi and from a pool of 32 females Aedes (Diceromyia) furcifer caught inside a forest gallery. Virus isolationI obtained by inoculation into suckling mice after amplification in Toxorhinchites. Identification was by IHA and complement fixation test. The two RVF strains were reisolated by inoculation in A. pseudoscutellaris (Mos 61) cells. No cytopathic effect was observed, the virus was detected by IFA. Of 360 residents within the area where the RVF viruses were isolated 2 have fluorecent antibodies (32 and 512).
These findings extend the range of known RVF virus circulatlon into Upper Volta and add A. cumminsi and A. furcifer to the list of mosquitoes implicated as possible vectors or RVF virus in Africa. Investigation on the medical and veterinary significance of CCHF and RVF viruses in the south of Upper Volta are in progress.