502 INFECTIOUS DISEASES DUE TO PROTOZOA 



Occurrence. — ^The disease is found principally among 

 young cattle on pastures, especially in wet seasons and during 

 the months of June to September. As the disease assumes 

 an enzootic or sometimes- an epizootic form, affecting a large 

 number of animals, and is not infrequently fatal, it assumes 

 economic importance. 



Etiology. — ^The cause is the Coccidium zuerni, which is 

 found in the feces of sick animals as round or oval protozoa, 

 varying in length from 10 to 25 microns. Under the micro- 

 scope they are highly light refractive and unstained appear 

 greenish-violet in color. 



Natural Infection. — Infection takes place through the 

 digestive tract, the coccidia being taken up with water from 

 pools and swamps and also probably with infested food. 

 Occasionally infection occurs in barns, especially when damp 

 and dirty. Young animals are much more susceptible than 

 older ones which, however, are by no means immune. The 

 disease is rarely seen in calves under six months, as they 

 are seldom exposed to infested pastures. Cattle ranging 

 from six months to two years of age are most often attacked. 



Necropsy. — The lesions are usually confined to the large 

 bowel, especially its posterior portion. The mucosa is 

 swollen, congested, often thrown into transverse folds (cor- 

 rugated), partially denuded of its epithelium, and spotted 

 with hemorrhages. Frequently masses of adherent epithe- 

 lium hang in shreds from the eroded mucous membrane. 

 The contents are a thin fluid, and vary in color from greenish 

 to reddish-gray or reddish-brown. Sometimes blood clots 

 are mixed with them. Over the mucosa a yellowish or gray- 

 ish fibrinous exudate is often noted. Due to secondary infec- 

 tion the small intestines may show hemorrhagic inflammation 

 or even necrosis. In the intestinal contents and mucosa 

 (especially in the loose shreds) nimibers of coccidia are found. 

 The cadaver is usually anemic and emaciated. 



Symptoms. — ^The period of incubation varies from one to 

 three weeks. A nmnber of young cattle on pasture may be 

 simultaneously affected; more rarely a whole herd may 

 develop symptoms in a single day. The principal symptom 

 is a suddenly appearing diarrhea, the feces thin, copious, 



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