Enteric protozoa in ruminants: diagnosis and control of Cryptosporidium, the role of the immune response.

Cryptosporidiosis is diagnosed by histological examination of tissues or microscopic examination of faecal material to reveal large numbers of endogenous or exogenous parasitic stages. The contribution made by Cryptosporidium to a diarrhoeal disease outbreak should be decided after testing for the presence of other known enteropathogens. Comparison between immunocompetent and immunodeficient animals with cryptosporidiosis indicates that immunity does influence the outcome of the disease; the latter group suffers persistent infection whereas the disease is transient in normal individuals. Experimental evidence from ruminant infections has shown that titres of secretory IgM and IgA rise in association with declining oocyst output; this evidence suggests that these antibodies act by preventing penetration of motile stages. Furthermore, experimental prevention of infection in infant mice and rats indicates that the role of passive lacteal immunity in ruminants deserves investigation.