Bovine coronavirus

Also known as coronavirus diarrhea in calves and winter dysentery in adult cows

Description

The coronaviruses are a very diverse family of RNA viruses. These are a type of virus in which the genetic information is stored in the form of RNA (as opposed to DNA). The coronaviruses are characterized by club-like spikes that project from their surface. The strains that cause respiratory disease in people and the strains that infect cattle are completely different. The bovine coronavirus is in group 2a and all the human respiratory coronaviruses have been in subgroup 2b.

Bovine coronavirus has been a problem in beef and dairy herds for many years, especially in young calves. There are three different but distinct disease syndromes caused by coronavirus in cattle. A syndrome is a set of medical signs which are correlated with each other and often associated with a particular disease or disorder.

Calf diarrhea is probably the most well-known cattle disease caused by bovine coronavirus. This virus can infect and kill cells that line the small intestine in a young calf, damaging the lining so it can’t absorb fluid and nutrients. The result is moderate to severe diarrhea that generally lasts four to seven days and is the most common sign of this disease.

Affected calves are usually between one and three weeks of age. Older calves generally have some resistance.  f diarrhea shows up in a calf older than three weeks, it’s generally due to some other type of infection, or mixed infection (some other pathogen along with the coronavirus).  

Winter dysentery is another disease in cattle associated with coronavirus. This is a highly contagious gastrointestinal disease, causing diarrhea in adult cattle. It usually affects cattle 2 to 6 years of age. Even though it’s most common in dairies, it has also been seen in some cow-calf operations and feedlots.  

The diarrhea appears suddenly, and spreads through the herd quickly.  In some instances the cows seem fine one day and by the next day a large number of them have blackish-green diarrhea, or passing blood clots instead of manure.

This type of diarrhea is most commonly seen in dairy cattle housed indoors in winter. The most common sign is explosive diarrhea in multiple animals within the milking herd, and the diarrhea often contains blood.
 
Affected cows go off feed, so their milk production may drop significantly. There is often a musty, severely unpleasant odor in the barn during winter dysentery outbreaks.

The bovine coronavirus is also associated with mild respiratory disease in cattle. Research suggests that coronavirus is involved in bovine respiratory disease complex, though there is conflicting information in veterinary literature about the actual role of bovine coronavirus in causing pneumonia in cattle.  

Some studies have produced pneumonia in calves, using experimental coronavirus infection. Some field studies show that the virus can be more commonly isolated from calves with pneumonia than from healthy calves.

It is still not clear whether the virus that causes calf diarrhea, winter dysentery, and respiratory disease are all the same or a bit different. The bovine coronavirus that causes these three distinct diseases may be the same virus or may have some slight differences.  

Signs

    Diarrhea and dehydration in baby calves less than a week old, lack of appetite, explosive bloody diarrhea (with unpleasant odor) in adult cattle, sometimes a nasal discharge in adult cattle.

Causes

The diarrhea in young calves and in adult cattle is caused by possibly different forms of the bovine coronavirus transmitted via feces (contaminating feed and water) but can also be spread via the respiratory tract, and there may be a mild nasal discharge.

Young calves in confined, contaminated areas are more likely to develop diarrhea from coronavirus than calves born out on large, clean pastures.

Winter dysentery is generally seen in cows that are closely confined with other cows. The number of cows in a herd that are affected with winter dysentery is generally very high, but mortality rate is low. The disease is generally mild and the cows recover fairly quickly.

Prevention

The best prevention against diarrhea in young calves caused by coronavirus is a clean environment and strong immunity in the calves. If a herd has trouble with scours in young calves, it pays to vaccinate pregnant cows ahead of calving so they provide a high level of antibodies in their colostrum. There are several different vaccines that can be given to pregnant cows (such as Calf-Guard—which can be given to pregnant cows or to baby calves, to protect against rotavirus and coronavirus—and ScourGuard which can be given to pregnant cows to protect their newborn calves against rotavirus, coronavirus and E. coli infections).  

Making sure calves get an adequate amount of high-quality colostrum soon after birth is the best insurance against scours caused by coronavirus, but there’s also an intranasal vaccine that can be given to newborn calves if there is some question about the adequacy of colostrum antibodies.

To prevent winter dysentery in cows, they should be in a clean environment with minimal stress. Cows in herds that have experienced winter dysentery in the past are most at risk for getting it again. Stress such as confinement, poor ventilation in barns, bad weather and a sudden drop in temperature may create more risk.

Sanitation is very important. Winter dysentery is often seen on farms that use the same loader buckets to load feed and also push manure.

Treatment

The best treatment for calves that get coronavirus is good care and plenty of fluids and electrolytes (administered often) to replace what’s being lost through diarrhea. If you can prevent severe dehydration and help the calf fight the disease, he will usually recover within a few days.  

Viral scours does not respond to antibiotics, but your veterinarian may prescribe a broad-spectrum antibiotic to protect the calf against secondary bacterial infections. A calf whose immune system is weakened by the viral infection is more vulnerable to an opportunistic bacterial infection in addition to the viral scours.

In adult cattle with winter dysentery there is no specific treatment other than keeping the cows hydrated with fluids, but actual death loss is usually low and the diarrhea typically resolves within a week or so.

Antibiotics are of no use for treating the virus; the main thing is to make sure the cattle have access to plenty of fresh water and highly palatable feeds (to encourage them to keep eating). Diarrhea should always be properly diagnosed by a veterinarian, since there are other diseases that could cause diarrhea—including salmonella, coccidiosis and sometimes BVD.