No abstract

In Tanzania Rift Valley fever (RVF) was first observed as an accidental human infection contracted during post-mortem examinations of dead calves (Newlands, 1957). Ever since no significant observations of the disease in the country have been reported. However, in 1978 a sudden storm of abortions occurred in various farms in Tanzania and this paper describes the isolation of the causative agent from aborted foetuses.The first report of 70 abortions came in June 1978 from a farm with a herd population of about 700 cattle at Iringa in the south of Tanzania. The abortions were observed one:to two days after vaccination with an inactivated quadrivalent foot-and-mouth disease vaccine. It was alleged that symptomless abortions and stillbirths took place at all stages of pregnancy. Later in the same year reports of similar abortion storms were received from Dar-es-Salaam, West Kilimanjaro and the islands of Zanzibar and Mafia. A few sheep abortions were also reported from Zanzibar.The affected farms were visited and detailed histories of the abortions were studied from records and post-mortem examinations of aborted foetuses were carried out. Sera from recovered animals and tissues from aborted foetuses were collected for laboratory investigations. Herdsmen were interviewed and many reported that they had suffered from headaches and influenza-like illnesses.Bovine foetal liver suspensions in phosphate-buffered saline (PBS) were inoculated intracerebrally into weaned mice which were killed when moribund, dissected and subjected to histological studies. Lamb kidney cell cultures were prepared with coverslips as described by Prydie and Coackley (1959). The tubes were inoculated with 0.2 ml of bovine foetal liver suspensions. Observations were carried out daily for cytopathic effects. Coverslips were stained with haematoxylin and eosin when the CPE was 70 to 80%.Sera to be tested were heated for 30 min at 56~ Complement fixation tests were performed using the technique modified by Matumoto, Iwasa and Endo (1950). Haemagglutination inhibition tests were performed according to the standard technique. The antigen was prepared from the Kabete vaccine strain of Rift Valley fever virus which was inoculated intracerebrally into weaned mice. When the mice were moribund, approximately 60 h after inoculation, livers were collected and 10% suspensions were prepared in PBS (pH7.2) with 1% foetal bovine serum. The test antigen was the supernatant fluid after centrifugation at 10,000rev/min for 30 min.Post-mortem examinations of aborted calves revealed hydrothorax, pulmonary congestion, hepatomegaly, subcapsular infarctions and petechiations on the liver. produced death in mice after two to three days and occasionally four to five days. The mortality rate was 100%. Clinical signs observed were apathy, anorexia, adipsia and laboured breathing. Towards the end of the third day the mice were hypersensitive and convulsive spasms preceded death. Subserosal haemorrhages were observed on dissection. Histologically the livers showed severe necro...