16/01/2020
Coccidiosis of Cattle
By Peter D. Constable, BVSc (Hons), MS, PhD, DACVIM, College of Veterinary Medicine, University of Illinois at Urbana-Champaign
Twelve Eimeria spp have been identified in the f***s of cattle worldwide, but only three (E zuernii, E bovis, and E auburnensis) are most often associated with clinical disease. The other Eimeria spp have been shown experimentally to be mildly or moderately pathogenic but are not considered important pathogens.
Coccidiosis is commonly a disease of young cattle (1–2 mo to 1 yr) and usually is sporadic during the wet seasons of the year. “Summer coccidiosis” and “winter coccidiosis” in range cattle probably result from severe weather stress and crowding around a limited water source, which concentrates the hosts and parasites within a restricted area. Although particularly severe epidemics have been reported in feedlot cattle during extremely cold weather, cattle confined to feedlots are susceptible to coccidiosis throughout the year. Outbreaks usually occur within the first month of confinement. Cows may contribute to environmental contamination of E bovis oocysts through a periparturient increase in f***l oocyst counts. Time to onset of diarrhea after infection is 16–23 days for E bovis and E zuernii and 3–4 days for E alabamensis; clinical disease due to coccidiosis does not typically occur in the first 3 wk of life. Coccidiosis is therefore not considered part of the neonatal diarrhea complex in calves.
The most typical syndrome of coccidiosis is chronic or subclinical disease in groups of growing animals. Calves may appear unthrifty and have f***l-stained perineal areas. In light infections, cattle appear healthy and oocysts are present in normally formed f***s, but feed efficiency is reduced. The most characteristic sign of clinical coccidiosis is watery f***s, with little or no blood, and animals show only slight discomfort for a few days. Severe infections are rare. Severely affected cattle develop thin, bloody diarrhea that may continue for >1 wk, or thin f***s with streaks or clots of blood, shreds of epithelium, and mucus. They may develop a fever; become anorectic, depressed, and dehydrated; and lose weight. Tenesmus is common because the most severe enteritis is confined to the large intestine, although pathogenic coccidia of cattle can damage the mucosa of the lower small intestine, cecum, and colon. During the acute period, some calves die; others die later from secondary complications (eg, pneumonia). Calves that survive severe illness can lose significant weight that is not quickly regained or can remain permanently stunted. Calves with concurrent enteric infections (eg, Giardia) may be more severely affected than calves with coccidia infections alone. In addition, management factors, such as weather, housing, feeding practices, and how animals are grouped, are important in determining the expression of clinical coccidiosis in cattle.
Nervous signs (eg, muscular tremors, hyperesthesia, clonic-tonic convulsions with ventroflexion of the head and neck, nystagmus) and a high mortality rate (80%–90%) are seen in some calves with acute clinical coccidiosis. Outbreaks of this “nervous form” are seen most commonly during, or after, severely cold weather in midwinter in Canada and the northern USA; there are no reports of the “nervous form” outside this geographic location. Affected calves may die
