Following completion of his Ph.D. degree, he held research positions in the Department of Virus Diseases, Walter Reed Army Institute of Research, and in the Virology Department of the SEATO Medical Research Laboratory, Bangkok, Thailand. He joined the faculty of the University of Wisconsin-Madison in 1968, with joint appointments in the Departments of Veterinary Science and of Wildlife Ecology, developing research and graduate training programs in epizootiology of infectious diseases of wildlife and domestic animals in Wisconsin and Latin America. Although now an emeritus professor, he continues to teach at the University of Wisconsin and at the Autlán campus of the University of Guadalajara , Mexico, where he is a visiting professor. He has been a virus diseases moderator for ProMED since 2007.