Antigenic analysis of Rift Valley fever virus isolates: monoclonal antibodies distinguish between wild-type and neurotropic virus strains.

Rift Valley fever virus (RVFV) isolates from southern Africa were analysed for possible strain variation using monoclonal antibodies prepared against the South African prototype RVF 1830 strain. By the indirect immunofluorescence antibody assay and neutralization tests, the wild type southern African isolates were found to be antigenically similar to RVFV strains from other parts of Africa. In contrast, differences in several biologically important neutralizing and haemagglutination epitopes on both the G1 and G2 glycoproteins of the attenuated Onderstepoort veterinary vaccine and the Smithburn neurotropic strain were identified.

Sindbis and West Nile virus infections in the Witwatersrand-Pretoria region.

From mid-December 1983 until mid-April 1984, there was an epidemic of Sindbis (SIN) virus infection in the Witwatersrand-Pretoria region in which hundreds of human cases were diagnosed clinically. Twenty-eight of these diagnoses were confirmed in the laboratory by seroconversion as being infections with SIN virus, and 5 cases of infection with West Nile (WN) virus were also found. Attempts to isolate virus from 66 patients, mainly from serum specimens, were unsuccessful. Infection rates for the mosquito vector Culex univittatus, collected at localities on the Witwatersrand in February and March, were mostly higher for both SIN and WN viruses than in previous years. The highest rates determined were 5.4 (SIN) and 9.6 (WN) per 1 000 mosquitoes. It is concluded that an epizootic of both viruses occurred which was manifested by a high level of viral activity in the feral Cx. univittatus-bird transmission cycle. Cx. univittatus efficiently transferred infection of SIN virus from this cycle to man to cause the epidemic of infection with that virus but it is unclear why there were apparently only a few cases of WN virus infection.

Prevalence of hepatitis virus and some arbovirus infections in Kavango, northern SWA/Namibia.

A survey of the frequency of hepatitis B markers in 258 subjects from Kavango, northern South West Africa/Namibia, was undertaken during February - May 1983. The hepatitis B surface antigen and hepatitis B e antigen carrier rates were 13,6% and 2,7% respectively. Only 1,9% of the subjects were negative for all the markers tested, indicating that infection had been present at some stage in 98,1% of the sample. No known transmission method of the virus seems to fit this high exposure rate. The possibility that arthropod transmission of the virus may play a role in the epidemiology of the disease in Kavango is being investigated. All subjects tested for antibodies to hepatitis A virus were found to give a positive result. Of the arboviruses tested for, West Nile virus was usually predominant and was probably responsible for most of the arbovirus infections. Antibodies to the Sindbis, Chikungunya, Germiston and Rift Valley fever viruses were also found.