His success at producing a vaccine to combat an outbreak of smallpox among the miners of the Witwatersrand brought him an appointment as state veterinarian for the Zuid-Afrikaansche Republiek, in which capacity he served during the Anglo-Boer War of 1899-1902. During this period his research team developed a vaccine against rinderpest, a malignant and contagious disease of cattle. His tremendous energy, pioneering spirit and professional integrity brought him international recognition.