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Farm Animal Practice
Protozoal disease in cattle and sheep
  1. Mike Taylor

    Mike Taylor is head of parasitology and ecotoxicology at the Veterinary Laboratories Agency, Weybridge, honorary lecturer in parasitology at the Royal Veterinary College, and visiting professor in veterinary parasitology at the University of Wales. His special interests include epidemiology and control of helminth and protozoal endoparasites, and ectoparasites, drug resistance, parasite pathology and parasite zoonoses.


PROTOZOA are ubiquitous single-celled organisms, of which over 65,000 species have been described. Many occur as either free-living forms or harmless commensals, but their numbers include some of the most globally important parasitic diseases of man and animals. Ruminants carry large numbers of protozoa in their stomachs and intestines, the vast majority of which are entirely harmless. Some species of protozoa, however, are significant as causes of disease in domesticated cattle and sheep, or because of their potential for zoonotic transmission. The parasites discussed in this article include Eimeria species, which cause coccidiosis in young ruminants; Cryptosporidum parvum, the cause of cryptosporidiosis in a wide range of mammals including ruminants and man; and Toxoplasma gondii, the causal agent of toxoplasmosis which produces abortion and fetal abnormalities in sheep and man. Reference is also made to a number of other protozoa found in cattle and sheep that either occasionally cause disease, assume importance as zoonoses, or are newly emerging infections.

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