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HEALTHY HERD IS BEST DEFENSE AGAINST CRYPTOSPORIDIOSIS

by: Heather Smith Thomas

Cryptosporidiosis is a protozoal disease that is similar to coccidiosis in several ways. Protozoa are one-celled animals and most kinds are harmless. But several types cause disease in animals and most of these are transmitted by the fecal-oral route; the protozoa are passed in the feces of an infected animal and are ingested by a susceptible animal via contaminated feed or water or when licking a dirty hair coat or suckling a dirty udder.

The protozoa that cause cryptosporidiosis are found almost everywhere. Various types infect humans, sheep, goats, deer, squirrels, etc. but only one type infects cattle. This same type can also infect humans. Another strain affects only humans. Several strains affect humans and various other animals but not cattle. Wildlife such as raccoons occasionally pass crypto to livestock.

These protozoa survive in moist conditions and can live for about 170 days in streams of water. They can also live on wet, contaminated calving grounds, but drying or freezing will eventually kill them. After being ingested, they multiply in the calf's intestine, causing diarrhea. It's rare to find this pathogen in calves older than four months old or in adults, but many beef and dairy calves are infected during their first months of life.

In earlier years, this disease was a problem only in dairy cattle and was estimated to affect up to 70 percent of dairy calves one to three weeks of age, with rate of infection on some farms as high as 100 percent. Now, however, this disease appears in beef herds as well. Though cryopto is often mild and self-limiting (runs its course without treatment and the animal recovers), it can be life threatening in any human or young animal with a compromised immune system or concurrent illness with some other disease.

In one study, five percent of cows tested were carriers, spreading a few protozoa continually in their feces. Thus these organisms are fairly common in the environment and in the water, on certain farms or ranches. The best defense against crypto is a healthy herd in good condition, in a clean environment. Herd health can be compromised by improper nutrition, so whenever you are dealing with crypto you also want to take a hard look at the trace mineral status of your animals—especially selenium and copper, since they are crucial to a strong immune system and seem to be especially important in whether or not cattle are susceptible to crypto.

This disease can be deadly if young calves are challenged with several pathogens at once, such as bacterial and/or viral scours along with the protozoa. Calves with severe, hard-to-treat diarrhea usually have mixed infections. Once you've had crypto on your place and the environment is contaminated, it is almost impossible to get rid of it. Each new crop of calves may become infected. Thus the best defense is a healthy herd, to keep animals from becoming sick with crypto in the first place.

THE DISEASE – The life cycle of cryptosporidia is different from that of coccidiosis. With coccidiosis, calves don't break with diarrhea until they are at least three weeks old. By contrast, a calf with crypto can develop diarrhea as young as four days of age if he was born in a contaminated place and ingests a large number of protozoa soon after birth. After an oocyst is ingested, it attaches to the intestinal lining to sporulate and multiply, similar to the multiplication stages of coccidia, but the incubation time for crypto is only two to seven days. Thousands of new oocysts are then passed in the feces for 3 to 12 days. Infection persists until the calf develops enough immune response to eliminate the parasite from the body.

When protozoa attach to the intestinal lining, white blood cells migrate to the site to fight off the infection, creating intense inflammation. The only way the calf can get rid of the pathogen is to get rid of the cell it's attached to, so the lining is shed. The raw gut can no longer absorb fluid and nutrients, so everything shoots on through, creating watery diarrhea.

Peak diarrhea occurs about three to five days after the calf ingests oocysts. The gut usually heals in a few days, but without intensive supportive treatment some calves will die from dehydration before the gut heals. Calves younger than three weeks of age usually take longer to regenerate damaged gut lining than an older calf, and the young ones also dehydrate more quickly.

Just like coccidiosis, after a calf gets over the infection he has some resistance. Even if he encounters the crypto protozoa again, he's less likely to get sick again but may continue to shed a few oocysts. Adult cattle usually don't become ill with crypto but can serve as a source of infection for calves.

SYMPTOMS – Calves with crypto usually have diarrhea, which persists for several days even if you treat them, since protozoa do not respond to antibiotics. The feces are usually watery, pale or greenish in color, but sometimes yellow, cream-colored or gray. The fluid feces do not contain blood because the damage is not that deep (in contrast to the bloody diarrhea of coccidiosis).

You may see mucus or shreds of tissue in the feces. The calf may be dull and not nursing. He may be dehydrated and/or show signs of gut pain. Persistent diarrhea may result in weight loss and emaciation. If complicated by concurrent infection with bacteria or viruses, the calf is usually much sicker. It may take diligent nursing care and frequent administration of fluids to keep him alive long enough for the gut to heal.

TREATMENT – There's no specific medication for crypto available on the market. Supportive care (fluids, electrolytes and good nutrition) can often save the calf if started early. If the calf is not nursing, he should be force fed milk or milk replacer as well as extra fluids, or he may become weak. Studies have shown that Banamine is also helpful, to reduce inflammation and to make the calf less miserable—so he'll be more apt to keep nursing his dam. IV fluids may be necessary for calves that are unable to absorb oral fluids.

PREVENTION – Make sure you never bring this bug to your place if you don't have it already. Since it's a common problem in dairy calves, don't buy dairy calves to raise on bottles or nurse cows, or to graft on beef cows that have lost their own calves—unless you are very sure the dairy calves are healthy and have never been exposed to crypto. Even if they look healthy, isolate them for five days after you bring them home, to be sure they are not incubating the disease. Then if they develop diarrhea you can clean up the isolation pen and haven't exposed other calves. Don't buy cows (beef or dairy) from any herd or farm known to have crypto.

If this disease is already on your place, keep all calving cows and young calves in a clean environment, so calves won't be exposed early in life by ingesting protozoa with contaminated feed or water, or nursing a dirty udder. If a pregnant cow lies in dirty bedding or on contaminated ground, she may get feces on her udder and the calf may ingest oocysts with his first nursing. The same precautions should be taken as for preventing spread of coccidiosis.

There is no vaccine that is very effective to prevent crypto, though researchers have been working on this. Control depends on cleanliness, avoidance of stress and crowding, and making sure cattle have clean feeding and bedding areas. Feeding areas should be continually moved to clean ground, if you are using round bale feeders or spreading hay on the ground.

Isolate any calf that develops diarrhea. Bring the cow and calf out of the herd to a “sick pen” so the calf won't spread oocysts and infect other calves. Keep them separate from the herd for several days after the calf recovers. Be sure YOU don't transmit the disease to other animals. Change clothes and footwear or rinse your boots in a disinfectant solution, wash your hands, and don't track feces from the sick pen to other locations.

Make sure every calf on your place gets adequate colostrum soon after birth. Even though cows don't produce many antibodies against protozoa, they produce some if they've been exposed to crypto, and this may give their calves some protection. In trials with crypto, the calves that had adequate colostrum were more difficult to intentionally infect with this disease. Healthy, unstressed calves with high levels of antibodies from colostrum also won't develop other diseases that might put them at risk for a serious case of cryptosporidiosis.

SIDEBAR: BE CAREFUL HANDLING SICK CALVES -- Cryptosporidiosis can be spread from calves to humans. Calves or humans in good health can usually handle exposure and not become ill. Very young calves or humans, or elderly people, or anyone with a compromised immune system may become seriously ill, however. Crypto can cause devastating illness in vulnerable people or calves, such as calves that did not get colostrum at birth. Be careful when treating sick calves so you don't inadvertently spread the disease to a vulnerable human. Wash your hands and change your clothes when you come indoors, especially if you have young children or elderly adults in your home.

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