ABSTRACT
Organisms of the genus Cryptosporidium are small coccidian parasites that invade and then replicate within the microvillous region of epithelial cells lining the digestive and respiratory organs of vertebrates. It is possible that in 1895 Clarke was first to observe a species of Cryptosporidium which he described as “swarm spores lying upon the gastric epithelium of mice”. In retrospect, the microbes he observed were probably the motile merozoites of C. muris, the type species named and described approximately 12 years later by the well-known American parasitologist, E. E. Tyzzer. Interest in Cryptosporidium by the veterinary medical profession has increased significantly since this protozoan was first reported in 1971 to be associated with bovine diarrhea. Studies of experimental infections in farm and laboratory animals clearly demonstrate that Cryptosporidium spp. are transmitted by environmentally resistant oocysts that are fully sporulated and infective at the time they are passed from the host.
