disease transmission | clinical signs | diagnosis | treatment | prevention
Introduction/Causative Agents:
Coccidiosis is a world wide contagious disease of cattle, especially young calves. The disease is caused by one or more different species of protozoa called Eimeria. These organisms parasitize and destroy cells lining the intestinal tract of the animal. Because each of the 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 coccidiosis.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 animal. The age of the animal is also important. This is 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 cow can continue to pass oocysts in the manure.
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 an animal 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. If a calf 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 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. Watery diarrhea is common and the calf may dehydrate rapidly. The diarrhea often contains mucus and blood. 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 calves 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.
Even though coccidiosis is typically a disease of the young growing calf, many adults are mildly infected and continuously shed oocysts which serve to infect the young calves. Occasionally, an adult animal shows temporary diarrhea when stressed or exposed to a new species of coccidia. This is especially common after an adult animal has been moved to another farm or is exposed to a new group of cattle.
Nervous coccidiosis, a neurological syndrome of calves and yearlings infected with Eimeria, can also occur. Animals with this type of disease will often be lethargic, incoordinated, and experience tremors and twitching. As the signs get worse, the animal may go down (become recumbent), froth at the mouth, bellow, and experience seizure-like activity. Often, diarrhea and straining to defecate precede the neurological signs. Even with aggressive treatment, these animals often die within 1-5 days of experiencing nervous system signs.
Diagnosis of coccidiosis can be based on clinical signs and microscopic fecal exams. Coccidiosis is so common that it should be suspected whenever calves 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 calves and adults with diarrhea may have worms rather than coccidiosis, or they may have both problems together.Coccidia oocysts can be identified if fecal material is mixed with a concentrated sugar solution. The oocysts float to the top along with larger worm eggs. They are collected and examined with a microscope (see page D220). Oocysts may be shed in the feces as early as 10 days after an animal is infected, but often the first attack of diarrhea occurs before oocysts are available to be identified. In these cases, the trained technician can do a direct fecal smear to look for smaller merozoites that do not float in the sugar solution.
If an animal dies of coccidiosis, necropsy examination will quickly give the diagnosis. The small intestine will have many irregular raised white areas, often about 1/8 to 1/4 inch in diameter. A smear taken from these white spots will show many coccidial forms if examined using a microscope.
Treatment: A variety of drugs may be given orally to treat an animal sick with coccidiosis. These include medications such as decoquinate, monensin, amprolium, and lasalocid. Usually, treatment is continued for about 5 days. Label and veterinary instructions should be followed because of the associated dangers if overdosed. All of these drugs are coccidiostats, which means that they slow down rather than kill the coccidia. Thus, if an animal is very heavily infected when treatment is begun, the medication may not help that much. These drugs will, however, greatly reduce contamination of the environment and thereby, give other animals time to develop immunity. In addition to the above medications, animals with nervous coccidiosis should receive 2-4 mL/kg of a calcium gluconate solution containing magnesium (CMPK or Cal-Dextro).
Medicating older animals or adults will temporarily reduce the passage of oocysts, but will not improve growth rates. Within 2 or 3 weeks after medication is stopped, coccidia levels will return to pretreatment values. Thus, except for protection of younger calves, it is not justifiable to treat older, apparently healthy animals that do not have diarrhea. It is far better to separate the young animals from these older carriers. It is neither possible nor desirable to completely eradicate coccidia from the adult animals.
Medication of apparently healthy calves is necessary on large farms with previous problems with coccidiosis. The aim is to prevent damage to the intestines rather than waiting for diarrhea to occur. For instance, it may help to treat the young animals with coccidiostats on a daily basis for a week or more before stressing them by weaning or by moving them onto pasture. In some herds, a drug such as amprolium may have to be given daily beginning at 2 weeks of age and continue until the young animals are several months old. Amprolium levels of 10 mg/kg (10 mg/2.2 lbs) daily should be used. It can be given to each calf individually or can be mixed with the food or water. For example, if there are 500 pounds of small calves in a pen, 2272 mg of amprolium is mixed with the water, milk or feed that they will consume in one day. The larger animals, by eating more, get more of the drug than do the smaller ones. Bovatec (lasalocid) at 30 grams per ton of feed in the starter grain has been found to eliminate the coccidiosis problems on some farms. Another potentially useful coccidiostat is Rumensin (monensin). This drug has protected calves when used at a minimum of 100 mg/head/day. The poultry industry has found that the coccidia often become resistant to a drug after 1 or 2 years. Cattle owners may also need to change drugs if the one in use ceases to be effective in controlling coccidiosis. Many of these products are very toxic to horses, so the medicated feed should not be left where a horse can eat it.
No matter what medication is chosen, it is important to consult a local veterinarian before attempting to use any of these products. Over-dosing can cause death. These products should not be used in lactating animals.
Prevention: Prevention of coccidiosis is very important in larger herds if young calves are to thrive. Once diarrhea has developed, most of the damage to the intestine that leads to stunted growth has already occurred. Sick, young animals are treated to save their lives and to limit contamination of the pens, but at this stage, the producer has already lost control of this contagious disease.
Several key facts are important to consider when developing a prevention program. The first is that adult animals are the original source of infection for young calves. The adults continually shed oocytes that contaminate the environment and younger animals. Because of this, all old bedding and feces should be removed from the calving pens before the new calves are born. Sporulated oocysts are commonly present on the skin of the udder, and the young, suckling animal may become infected at the same time it takes its first drink of colostrum. To prevent this from happening, the female’s udder should be washed and dried before the young nurse, or the calf should be removed from its dam at once and bottle-fed the colostrum. If very few cows are present on a farm and the pens are dry and spacious, coccidiosis is not likely to be a problem. In larger herds where severe problems exist, it is sometimes best to raise offspring completely separate from the adults.
Fecal contamination of feed and water must be prevented. This means that feeders and waterers should be outside the pen whenever possible and arranged so that manure can not fall into them. Grain should be fed in areas where manure contamination can be kept to a minimum.
Because oocysts have to sporulate to become infective, exposure can be reduced by cleaning the pens daily. Because moisture is necessary for sporulation, concentrate on keeping the pens very dry and fixing leaking waterers at once. Small, grassy pastures are also very dangerous and should be used with caution. It is very important to avoid overcrowding; spreading the calves out decreases the number of oocysts on any given square inch of pen floor or pasture. If many calves are present on the same farm, they should be grouped by age. Putting a 2-week-old calf into a pen with calves 2 months old, where coccidial numbers and immunity have been building up for some time, is to invite disaster for the newcomer. Oocysts are killed by very cold temperatures (far below zero) or by hot, dry conditions above 104° F. This means that at the end of the calving season, pens and feeders could be moved out into the hot sunshine for some natural sterilization. Ordinary disinfectants do not destroy oocysts and should not be relied on for control of coccidia. Formaldehyde, ammonia, or methylbromide can kill oocysts.