Cryptosporidium in cattle: Assessing the zoonotic risk.

Cattle infected with Cryptosporidium can shed large quantities of the environmentally resistant oocysts, which can cause significant diarrhoeal disease, particularly in neonatal calves and in susceptible human populations worldwide. More than ten species of Cryptosporidium have been reported in cattle; however, C. parvum dominates in young calves in many countries, with C. ryanae, C. bovis and C. andersoni prevalent in older animals. Cryptosporidium hominis and C. parvum are the main species infecting humans. In most countries, zoonotic cryptosporidiosis is primarily caused by C. parvum IIa subtypes, which also dominates in calves, but in China, C. parvum infections in cattle are exclusively caused by IId subtypes. Outbreak investigations and molecular epidemiological studies support calves as a major source of zoonotic cryptosporidiosis. The zoonotic significance of increasing reports of C. hominis in cattle requires further investigation. Epidemiological investigations designed to better understand the sources and transmission dynamics using improved typing tools are required before better control strategies can be implemented.