R. P. Herd

Review of equine Cryptosporidium infection.

Diarrhoea is one of the most important diseases of foals and 7 0 4 0 % are affected within the first 6 months of life (Palmer 1985). Although the cause is multifactorial and changes in the physiology and nutrition of foals are sometimes responsible, diarrhoea is frequently the result of infection by enteropathogens such as bacteria, viruses and nematodes (Palmer 1985; Tzipori 1985). There is increasing evidence that Cryptosporidium infection can also cause diarrhoea in foals (Austin et a/. 1990; Kim 1990). Cryptosporidiosis in horses is caused by Cryptosporidium parvum, a coccidial parasite infective to mammals. C. muris has been reported in foals in Italy (Canestri-Trotti and Visconti 1985). but its identity was questionable because the reported size of oocysts was within the range of C. paivum (Kim 1990). Like other coccidia, the infective stage for Ciyptosporidium is the sporulated oocyst. Unlike the others, the sporulation of Ciyptosporidium occurs within the microvillous border of the small intestine. Therefore, newly excreted Cryptosporidium oocysts are infective to other hosts immediately. In addition, there are two types of oocysts in Ciyptosporidium: ( I ) thin-walled oocysts that exist within the intestine shortly after their formation and re-initiate infection (autoinfection), and (2) thick-walled oocysts that are excreted in faeces and are responsible for the transmission of infection from one animal to another (Current and Garcia 1991).