Veterinarians discuss the effects and treatment protocols of protozoan diseases
Scours in calves can be caused by many different things. The most common causes are intestinal infections – which may be bacterial, viral or on some cases, due to tiny one-celled protozoan parasites.
Most protozoa encountered in the environment are harmless. But several types can cause disease, and most of these are transmitted by the fecal-oral route – passed in feces of an infected animal and then ingested by a susceptible animal via contaminated feed and water, when licking a dirty hair coat or suckling a dirty udder. Cryptosporidiosis and coccidiosis are examples of protozoan diseases affecting calves.
Various types of cryptosporidium can infect humans, sheep or other animals, but Cryptosporidium parvum infects cattle and can also infect humans.
Geof Smith, a former professor at North Carolina State University, says stockmen need to understand this intestinal infection is hard to prevent or treat because it’s not viral or bacterial.
“We’re probably never going to have a good vaccine, since there are almost no vaccines for protozoal diseases,” he explains.
Treatment is also challenging
Smith says, “Unlike bacteria, we can’t kill protozoa with antibiotics. We don’t have any drugs in this country shown to work as an effective treatment for crypto.”
It therefore comes down to management – nutrition, hygiene and trying to minimize fecal-oral contact. The best defense against crypto is a healthy herd in good condition, and a clean environment. Herd health can be compromised by inadequate nutrition, so if producers experience crypto, Smith encourages to look at trace mineral status – especially selenium and copper since those are crucial to a strong immune system.
“We also see problems when there’s overcrowding in a calving pasture or snow and bad weather. If stockmen keep moving the cows calving to clean pastures and have calves born in clean areas, this disease can be minimized. The later-born calves in contaminated pastures are the ones that get sick,” he says. “These protozoa don’t live in the environment forever, but can live several weeks or months.”
After being ingested, they multiply in the calf’s intestine, causing diarrhea. Calves are generally infected during their first weeks of life.
“This is a disease of young calves, especially one to three weeks of age. It’s not something producers will see in calves three or four months old,” Smith says.
This is different than coccidiosis, which takes several weeks’ incubation to affect a calf. Coccidiosis may not show up until a calf is at least four weeks old and can affect older calves, he continues.
In a herd, there may be several calves picking up a few oocysts, but whether they get sick may depend on how much they are exposed to.
“This is similar to coccidiosis. It’s not uncommon for a calf to have a few oocysts; it’s when they get loaded up we start to have problems,” says Smith.
Crypto is often mild and the animal can recover without treatment, but it can be life-threatening in any human or young animal with a compromised immune system or concurrent illness. Crypto 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.
“If calves get diarrhea, try to keep them hydrated and provide good supportive care. Antibiotics probably won’t be helpful,” says Smith.
David Rethorst, veterinarian with Beef Health Solutions in Wamego, Kan. adds, in order to save these calves producers need a good electrolyte solution high in bicarb content.
“Give two quarts, three to four times a day,” says Rethorst. “The more often, the better. Producers can’t overdo the fluid and electrolytes for these calves because they are dehydrating so quickly.”
Try not to bring crypto to the ranch. Since it’s most common in dairy calves, don’t buy dairy calves to raise on bottles, nurse cows or to graft on beef cows which lost their calves – unless producers are sure the dairy calves are healthy and have never been exposed to crypto.
Even if cattle look healthy, isolate them for five days after bringing them home to be sure they are not incubating the disease. Then, if they develop diarrhea, producers can clean the isolation pen and haven’t exposed other calves.
Heather Smith Thomas is a corresponding writer for the Wyoming Livestock Roundup. Send comments on this article to firstname.lastname@example.org.