Cryptosporidium is a protozoal parasite that lives in the intestines of many animal species.
It can also be passed from one species to another, including cattle to humans, which has prompted controversy. Do cattle grazing close to human water sources pose a threat to public health?
Many people confuse coccidiosis with “crypto.” Though these parasites are related, there are important differences:
- Coccidia can only strike calves older than four weeks, while crypto can cause diarrhea in calves as young as five days old.
- Coccidiosis can be managed with common sulfa antibiotics while crypto is immune to all drugs.
- Coccidia tends to infect calves that do not get adequate colostrum. There is no link between colostrum intake and crypto infections.
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Like many viruses and bacteria that attack the intestine, crypto causes diarrhea and loss of appetite. The diarrhea may be mild, just a slight looseness to the feces, or it may be severe, containing blood, mucous and undigested milk. No matter what form, crypto diarrhea characteristically lasts six to 10 days and can’t be treated with antibiotics.
Because there is no specific treatment for crypto, supportive care is vital. Calves should be given fluid therapy for the duration of the disease and they must be given milk as an energy source because they have so little reserve at that age.
The presence of crypto in a herd can be confirmed by analyzing fecal samples from calves when they are 12 days old. With natural infections, a large percentage of calves are shedding billions of crypto eggs called oocysts in their feces by this age. Studies show that about 20 percent of calves with diarrhea routinely shed oocysts. Between two to nine percent of calves with no diarrhea also shed crypto oocysts.
Calves become infected by picking up the organism from their contaminated environment. The only way to prevent infection is to limit exposure. This is difficult because the oocysts are hardy survivors.
Cattle producers can contract crypto by handling calves with diarrhea. As well, people can get it from contaminated water.
Researchers at the University of California, Davis asked whether infected calves are a primary source of surface water contamination and human infection.
They had to determine how long oocysts survive. Crypto oocysts remain viable for only a few hours when they dry out. In freezing conditions, more than 90 percent of crypto oocysts are noninfective after 10 days. If oocysts go directly into stream water, 60 percent are still viable after 33 days but less than 10 percent are infective 176 days later.
It would appear that few oocysts can remain infective long enough to make the journey from a calf, through an extensive water supply system, to a person.
Crypto is, however, prevalent in many water systems. In a survey of surface water in the western United States, 77 percent of samples were found to contain crypto oocysts.
In a study that compared protected water and those subject to agricultural runoff, similar concentrations of crypto oocysts were found in both. It is unclear whether cattle pose a significant crypto threat to people, but we do know they are not the only source of contamination.
Jeff Grognet is a veterinarian and writer practising in Qualicum Beach, B.C.
