Coccidiosis is a world wide contagious disease of sheep and goats, especially young lambs or kids. The disease is caused by one or more of approximately 12 different species of protozoa called Eimeria. These organisms parasitize and destroy cells lining the intestinal tract of the animal. Because each of the 12 or so coccidia species is completely independent from the others, with no cross immunity, an animal that is living with one type of coccidia may develop diarrhea when exposed to a different type. Good nutrition (including vitamin E-selenium supplementation in selenium deficient areas) also helps the animal defend itself against
Whether or not an animal gets sick with coccidiosis depends on several factors. One is the number of oocysts (eggs) swallowed at one time. Small exposures, frequently repeated, lead to immunity; while large exposures destroy all the intestinal cells at one time and may kill the lamb or kid. The age of the animal is also important, partly because the older animal has usually had time to develop some immunity, while the younger animal can be very vulnerable to disease. Immunity to coccidiosis in healthy adult animals is rarely complete, yet most of the intestinal cells in the adult are safe from invading coccidia. This means that a healthy looking adult sheep or goat can continue to pass oocysts in the fecal pellets.
Disease Transmission and Life Cycle: An infected animal sheds thousands of microscopic coccidial oocysts (eggs) in its feces every day. When first passed, the oocysts are harmless to another animal. However, under favorable conditions of warmth and moisture, each oocyst matures (sporulates) in 1-3 days to form infective sporozoites. If a young lamb or kid swallows the sporulated oocyst, the sporozoites are released and rapidly penetrate the intestinal cells. From here on the life cycle gets very complicated. The coccidia pass through several periods of multiplication during which large schizonts are formed. The intestinal cells of the animal are destroyed and thousands of merozoites break out and invade other intestinal cells. Eventually, sexual stages are reached and new oocysts are produced. The entire life cycle of the protozoa, from oocyst to new oocyst, takes 2-3 weeks.
Clinical Signs: If a young lamb or kid is suddenly exposed to many sporulated oocysts, it may become severely ill 1-2 weeks later. It will be off feed, listless, and weak. It may show abdominal pain by crying or getting up again as soon as it lies down. At first, the young animal might have a fever, but later the body temperature is normal or even below normal. Diarrhea begins pasty, then becomes watery, and the lamb or kid may dehydrate rapidly. In contrast to calves, lambs and kids only rarely have bloody diarrhea. Because the lactic acid produced by the digestion of milk helps to inhibit coccidia in the nursing young, signs often appear 2-3 weeks after the animals are weaned. Many of these signs are brought on by the stress of weaning or overcrowding.
Young lambs or kids may be killed quickly by a severe attack of coccidiosis. The stronger or less heavily infected animals will develop a chronic disease characterized by intermittent diarrhea and poor growth. Tails and hocks are often dirty. Because the intestines have been severely damaged, the animal with chronic coccidiosis cannot digest its feed properly. As a consequence, such an animal will be a pot-bellied poor-doer for months afterwards. Frequently, a stunted lamb or kid will be too small to breed its first winter.
Even though coccidiosis is typically a disease of the young, growing lamb or kid, many adults are mildly infected and continuously shed oocysts which serve to infect the young lambs and kids. Occasionally, an adult sheep or goat shows temporary diarrhea when stressed or exposed to a new species of coccidia. This is especially common after the ewe or doe has been boarded on another farm for breeding.
Diagnosis: Diagnosis of coccidiosis can be based on clinical signs and microscopic fecal exams. Coccidiosis is so common that it should be suspected whenever lambs or kids older than about 2 weeks of age are scouring. Sudden dietary changes or excessive food consumption can also cause diarrhea and make the animal more susceptible to coccidiosis. Diarrhea that begins with the consumption of too much milk, grain, or lush grass may drag on for days because of coccidiosis. Older lambs/kids and adults with diarrhea may have worms rather than coccidiosis, or they may have both problems together.
A variety of drugs may be given orally to treat the lamb or kid sick with coccidiosis. These include medications such as sulfamethazine, sulfadimethoxine, amprolium, and lasalocid. Usually, treatment is continued for about 5 days.