Cryptosporidium in cattle: Assessing the zoonotic risk

Cattle infected with <i>Cryptosporidium</i> can shed large quantities of the environmentally resistant oocysts<i>,</i> which can cause significant diarrhoeal disease, particularly in neonatal calves and in susceptible human populations worldwide. More than ten species of <i>Cryptosporidium</i> have been reported in cattle; however, <i>C. parvum</i> dominates in young calves in many countries, with <i>C. ryanae</i>, <i>C. bovis</i> and <i>C. andersoni</i> prevalent in older animals. <i>Cryptosporidium hominis</i> and <i>C. parvum</i> are the main species infecting humans. In most countries, zoonotic cryptosporidiosis is primarily caused by <i>C. parvum</i> IIa subtypes, which also dominates in calves, but in China, <i>C. parvum</i> 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 <i>C. hominis</i> 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.