Crypto presents a number of challenges for vets and producers

These protozoa are difficult to detect so vigilance is needed to spot and deal with outbreaks

The incidence of ‘crypto’ diarrhea is most definitely higher on dairy farms where calves are raised in close confinement and the wet or moist environment is conducive to the transmission of these protozoa.

But large-animal veterinarians are also detecting it more often in our beef herds out west.

Crypto is a protozoa with a very similar life cycle to coccidia, which is probably much more familiar to Canadian cattlemen. The detection can be difficult, but with newer tests and other methods, you may find it even in well-managed cattle operations. Dairymen watch for it diligently and beef producers should discuss it with their veterinarians. Be especially vigilant if scours crops up in older calves that seem unresponsive to traditional scour treatments. Bringing in dairy calves to be adopted onto beef cows can be a source of infection. I always suggest using calves from your own herd if possible.

Crypto usually is caused by the species C. Parvum in cattle and it is also zoonotic — meaning it is transmissible to humans, with most cases resulting from exposure to sick calves. So watch when handling diarrheic calves and be extra vigilant when cleaning and disinfecting the area calves have been in. As with all zoonotic diseases, people under stress or immunosuppressed are highly susceptible. Make sure — especially after dealing with any diarrheic calves — to clean boots, coveralls, and wash your hands thoroughly. Treat the diarrheic calves last to avoid carrying the oocysts (eggs) between calves.

The organism is very similar to coccidia in the sense oocysts are passed in the manure in very large numbers (up to 10 million per gram of manure). Oocysts are ingested by the calf and in completing the life cycle cause damage to the large intestine and the end of the small intestine. We see it primarily in calves anywhere from three to 30 days of age. The clue is calves, which seem unresponsive to treatment and the diarrhea is generally yellow and sort of foamy. The organism destroys the inner lining of the intestine, so the milk comes through essentially undigested and calves dehydrate.

Keep in mind that half the time crypto is involved in mixed infections with other scour organisms, so you may be dealing with essentially two diseases at the same time. That is why one must use all the preventive steps in your power to avoid a scours outbreak. All the tools we have talked about in other articles such as new calving area; lots of room and bedding; and good nutrition of the dam (leading to high-quality colostrum) all help in prevention. Make sure the calves are up and sucking within a couple of hours and if in doubt, supplement with home-stored frozen colostrum or the good colostrum substitutes such as HeadStart. Scours vaccinate your cows and heifers, but keep in mind good scours vaccines cover the most common causes of viral and bacterial scours in calves but not ones caused by protozoan (coccidia and cryptosporidiosis).

Initial diagnosis has been an issue in the past. Veterinarians investigating scours outbreaks have often suspected crypto was involved but it was hard to prove. There are several ways to prove its existence. Fecals can be done and the labs are getting better at spotting it but like coccidia, its oocysts are much smaller than worm eggs and are hard to see even with a microscope. Now there is a check done with a strip inserted into the manure called Entericheck by Biovet Labs, which is a fairly sensitive and specific check. We learned from a recent veterinary student from Calgary (now Dr. Dayna Goldsmith) attending our clinic on a rotation that crypto is what they call an acid-fast organism. This means it takes up acid-fast stain, so another test the vet clinic can do is smear a sample of the manure on a microscope slide, stain it and — like magic — the oocysts become very visible when they take up the stain. This worked very well at our clinic. (Veterinary clinics can order the acid-fast stain.) The combination of these three methods has greatly improved the diagnostic rate of crypto.

The next issue with crypto has been treatment — or should I say lack of treatment — options.

Standard treatments such as electrolytes are always warranted. Vets would prescribe sulfa drugs similar to coccidiosis treatment but the best way is to cut down the number of organisms being excreted. A Merck Animal Health product called Halocur — which has been used in Canada for a few years under an experimental drug release — controls crypto by breaking the life cycle and substantially reducing the number of oocysts produced. Halocur is an oral product (given at two cc per 10 kg daily), and it is very important to dose it carefully as unlike most products, the safety margin is quite low. At twice the dose, you could get depressed calves, blood in the diarrhea, and other signs very similar to the disease itself so discontinue medication if those signs show up. At four times the dose, the medication can be fatal. Always treat calves on a full stomach and don’t start treatment if they are already feeling sick.

Isolation of sick calves and a good cleaning, washing and disinfection of the isolation area are also necessary. The oocysts are very resistant and are killed by high temperatures. The key is keeping the oocysts numbers down. With age, resistance develops and that is why you never see this disease in older cattle.

There are other coccidiostats, which have been tried against cryptosporidiosis on an experimental basis with some decent success (in fact Halocur was developed as a coccidiostat for chickens). If you see unusual-appearing diarrhea with the frothy content appearing like undigested milk, make sure your veterinarian rules out cryptosporidiosis because the treatment is much different than the other neonatal diarrheas. Your local veterinarian would be best to help diagnose crypto and give you the treatment options most likely to be successful in your operation. Here’s hoping for a crypto-free calving season.

About the author

Contributor

Roy Lewis practised large-animal veterinary medicine for more than 30 years and now works part time as a technical services veterinarian for Merck Animal Health.

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