Science and popular participation in the investigation of heartwater in South Africa, c. 1870-1950.

During the late nineteenth century, settler farmers in southern Africa identified heartwater as a damaging disease of small stock and cattle. They advanced various explanations of the disease, including the theory that it was caused by the bite of ticks. Around 1900, the American entomologist C.P. Lousbury demonstrated that heartwater was transmitted by the bont tick. He also worked out the life cycle and life habits of the tick. Subsequently, farmers developed methods of controlling ticks by dipping animals in solutions of arsenic. By 1910, the practice of dipping cattle had become very widespread over much of southern Africa. The expansion of the practice was greatly stimulated by the coming of the deadly tick-borne disease, East Coast fever. At this time, veterinary scientists attempted to develop a vaccine against heartwater, but with little success. Little further progress was made until the 1920s, when the American scientist E.V. Cowdry identified a causal agent, Rickettsia ruminantium, while on a research secondment to South Africa. By the 1940s, South African veterinary scientists had devised methods of immunising stock against heartwater, but there remained considerable technical difficulties and their use remained limited. Dipping in arsenic solutions to attack the tick on the animal thus remained the most important means of controlling disease in the first half of the twentieth century.