oa South African Medical Journal - Rift Valley fever in South Africa : 2 : the occurrence of human cases in the Orange Free State, the North-Western Cape Province, the Western And Southern Transvaal : B : field and laboratory investigations
An extensive epidemic of Rift Valley fever affected the sheep, cattle and probably wild buck, in the Western Free State, North-Western Cape Province, and the Western and Southern Transvaal in the autumn of 1951. At the same time many human cases of an acute illness, at first thought to be influenza, but later proved to be Rift Valley fever, also occurred. The illness was characterized by an incubation period of four to six days, a sudden onset and a short but severe illness with painful limbs, backache and headache and high fever, often showing a biphasic temperature chart. There were no fatal cases. Several patients developed defects of vision associated with exudates in the retina soon after their acute illness. A virus having the characteristics of the virus of Rift Valley fever was isolated from blood collected from one of the patients during the acute stage of the illness. The blood of the convalescent patients tested gave a positive complement fixation test for Rift Valley fever. None of several wild rodents and birds, which were tested were incriminated in harbouring the infection. The virus was not isolated from several batches of mosquitoes, including Culex theiferi, Aedes caballus. Rift Valley fever had not been known to occur in South Africa before this epidemic, the origin of which remains obscure. It is possible that the infection was introduced by air traffic or by direct contiguity spread from Central Africa. These possibilities, as well as the possibility that the infection may be endemic in certain forest areas of South Africa, require further study. The need for developing a prophylactic vaccine to control the disease is emphasized.
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