Characterization of Palyam serogroup orbiviruses isolated in South Africa and serologic evidence for their widespread distribution in the country.

The finding that there had been multiple isolations of Palyam serogroup orbiviruses from aborted cattle fetuses in neighbouring Zimbabwe, suggested that there was a need to investigate the possible occurrence of the viruses in South Africa. Unidentified viruses isolated in South Africa, which had been in storage, were examined. Four viruses which had been isolated from Culicoides midges collected at various sites in the years from 1969 to 1977, were identified as three strains of Gweru virus and one of the Nyabira virus (Palyam group serotypes originally described from Zimbabwe). A fifth virus, isolated in 1967 from the blood of a cow with mild fever, was found to be a distinct new member of the Vellore antigenic complex of the Palyam serogroup and was named Apies River virus. Sera from 476 cattle, 150 sheep, 24 goats and 78 humans from 10 farms were tested for neutralizing antibodies to the above three serotypes of virus plus Abadina and Marondera serotypes. Only 1 of 100 cattle sera from two farms in the southern coastal area had antibody, but elsewhere there was a high prevalence of antibody with 254 (53%) of all cattle exhibiting activity for one or more of the five serotypes of virus tested. Only 6 (4%) sheep, 3 (12.5%) goats and 11 (14%) humans had antibody.