Max Theiler health at the Yale School of Medicine and the School of Public Health from 1964 to 1967. After passing the yellow fever virus through laboratory mice, Theiler found that the weakened virus conferred immunity on rhesus macaques. The stage was set for Theiler to develop a vaccine against the disease. Theiler first devised a test for the efficacy of experimental vaccines. In his test, sera from vaccinated human subjects were injected into mice to see if they protected the mice against yellow fever virus. This "mouse protection test" was used with variations as a measure of immunity until after World
Arnold Theiler sickness with a combination of live virus and equine antiserum. This disease is now known to be caused by a pegivirus. Theiler was the first Director of the Onderstepoort Veterinary Research Institute, outside Pretoria. This institute under his leadership carried out research on African horse sickness, sleeping sickness, malaria, East Coast fever ("Theileria parva") and tick-borne diseases such as redwater, heartwater and biliary. The University of Pretoria Faculty of Veterinary Science was established there in 1920 which enabled veterinarians to train locally for the first time. Theiler became the first dean of this faculty. He married Emma Sophie Jegge (1861–1951)