Veterinary Immunology as Colonial Science: Method and Quantification in the Investigation of Horsesickness in South Africa, c. 1905-1945

This article examines the practice of veterinary immunology in South Africa during the first half of the twentieth century through an analysis of research into a horsesickness vaccine at the Onderstepoort Veterinary Institute. From the early 1900s, Arnold Theiler prioritized research into horsesickness, by then defined as an insect-borne disease caused by an ultravisible virus. He succeeded in devising a means of prophylaxis using a simultaneous injection of infective blood and immune serum, but he discovered antigenically different strains of the virus, which could overcome the immunity produced by his treatment. The practical value of Theiler's methods was further limited by difficulties in standardizing the biological material used in immunization, the results of which remained too erratic for application on a large scale. No further advances were made until the 1930s, by which time Onderstepoort had been drawn more closely into international scientific networks. Using techniques derived from research into yellow fever in America and canine distemper in Britain, the Onderstepoort scientist Raymond Alexander invented a method of immunization that utilized the propagation of the horsesickness virus in the brains of mice. Alexander's methods, which were characterized by successful technical adaptation and innovation, depended upon methods of quantification first developed by Paul Ehrlich to standardize diphtheria antitoxin during the 1890s. During the 1940s, vaccination expanded rapidly in South Africa, and Onderstepoort later exported the vaccine and associated technology to other countries affected by horsesickness.