Neutralizing Antibodies to Arthropod-Borne Viruses in Human Beings and Animals in the Union of South Africa

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Abstract
Summary: Sera collected from indigenous residents representing 51 localities in 44 zones of the Union of South Africa were tested for neutralizing antibodies against West Nile, Bwamba, Semliki, and Bunyamwera viruses. Similar tests with 5 other viruses were done with sera of residents representing selected localities. A total of 7,553 serum-virus tests were done, with a protective sera percentage of 2.6. Highest incidence of sera protective against Sindbis and West Nile viruses was found in the elevated plateau region 3,000 ft or more above sea level. The converse was true of results with Bwamba and Bunyamwera viruses, in which case the highest incidence of positive sera was in donors residing in regions usually coastal at less than 500-ft elevation. A brief description is given of two localities, Luckhoff on the plateau structure and Simbu Pan on the coastal fringe, which illustrate geographic and climatic differences that may be correlated with immunologic results. Sera from 9 of 63 donors from Durban were protective against type I (Hawaiian) dengue fever virus. Their age distribution is serologic evidence that the recorded outbreak of dengue fever in Durban in 1926–27 was due to that virus. None of the sera tested against Ntaya and type II (New Guinea) dengue fever viruses was protective. Sera from monkeys trapped in various localities in the Union were also tested. Of 413 sera tested, 78 had West Nile neutralizing antibodies. Negative results were obtained in 558 serum-virus tests with sera from a sample of the same monkeys against 5 other viruses. Domestic animal sera collected on a farm near Johannesburg and specimens from immature birds collected on three lakes also near Johannesburg were found to have neutralizing antibodies against Sindbis and West Nile viruses. Indications were that the antibodies in the avian sera were of passive origin.