Cryptosporidiosis in bovine and human health.

Cryptosporidiosis, which is caused by Cryptosporidium parvum and was discovered in mice at the turn of the century, emerged as a frequently reported intestinal disease of animals and humans in the 1980s when its zoonotic potential was recognized. In recent years, the public has become aware of severe cryptosporidiosis because of its incidence in AIDS patients and because of massive outbreaks of cryptosporidial enteritis among the general populace worldwide from contaminated drinking water. Livestock and human wastes that were laden with oocysts of cryptosporidia have been incriminated in some cases. Intestinal cryptosporidiosis of livestock causes a brief diarrheal disease and probably does not hinder lifetime production in most cases. However, serious disease and deaths may sometimes result from complications from other pathogens and various other detrimental factors. Adolescent and adult cattle can carry C. parvum but probably do not shed large numbers of the parasite. However, certain cattle of all ages shed billions of the apparently nonzoonotic Cryptosporidium muris, which also was first discovered in mice around the turn of the century. Cryptosporidium muris infects only the glands of the stomach (abomasum in cattle), usually causes no overt illness, but retards acid production. Protein digestion in the abomasum probably is retarded, and, in fact, milk production in cows that are chronically afflicted with C. muris is reduced about 13%. Growing calves may be adversely affected also. Therefore, as concerns the dairy industry, the discussion of cryptosporidia involves efficient cattle agriculture, public health, and the environment.