One Nasty Bug
How to battle one of the most prevalent pathogens in the cattle industry — bovine coronavirus
By Nicole Lane Erceg
A microscopic predator has found its home on America’s ranches. It does not live in the soil or pastures but makes its way from herd to herd catching a ride inside the bodies of ruminant wildlife and seemingly healthy cattle.
For more than 50 years, this unpleasant microorganism has plagued the cattle industry and has been associated with neonatal calf diarrhea, winter dysentery and most recently, bovine respiratory disease (BRD).
Fortunately, as the bovine coronavirus (BCV) evolves, so does research and technology, opening the door for improved methods of disease prevention.
The prevalence of BCV in the cattle industry makes it more than a run-of-the-mill pesky pathogen. This enteric and respiratory disease-causing virus is the leading bug affecting neonatal calves. Most severe during the winter months, BCV continues to be a major problem for cattle producers, causing disease and economic losses in the cattle industry worldwide.
As the old saying goes, an ounce of prevention is worth a pound of cure and Dr. Guy Ellis, D.V.M., ruminant technical services veterinarian for Merck Animal Health, says this is especially true when battling BCV, since there is no medication option for treatment of a virus.
“When it comes to coronavirus, the bottom line is that the virus is everywhere and a good prevention program can be of benefit for most cattle producers,” says Ellis.
In his more than 20 years of experience as a cattle veterinarian in the Texas Panhandle, Ellis says the most prominent symptom of a BCV infection he sees is diarrhea in calves 3 weeks of age or younger. However, a growing body of research indicates that BCV could also be a contributor to BRD since the virus can cause both enteric and respiratory infections.
“We are seeing bovine coronavirus more and more from both an enteric as well as respiratory standpoint in cattle,” says Ellis.
BCV is most often spread by animals during times of stress including calving, shipping, weaning, commingling and during cold weather. A highly contagious virus, BCV can spread through the herd quickly and affect entire calf crops. Adult cattle can be carriers of the virus and shed the pathogen in their feces, easily infecting neonatal calves.
While there are no medications that can directly treat a BCV infection, prevention in the cow herd and in the calf can be the key to preventing loss.
The best treatment is prevention
The first step to avoiding BCV infections in young cattle is implementing a pre-calving vaccination program in pregnant dams. By stimulating an immune response in the dam, she can pass on her immunity to the calf through the first milk — colostrum. The maternal antibodies give the calf direct immunity from the virus before an infection can take place.
“If you don’t address the herd level immunity of your cows, then those carriers can spread them each year to your calves,” says Ellis.
He also recommends avoiding pasture crowding during calving and limiting commingling of older and newborn calves, because an infection in a small number of calves can easily spread.
“BCV is most prevalent when cows are concentrated in a pasture for calving, which can cause it to spread rapidly, so the more concentrated your cows, the more apt calves are to have this issue.”
For ranchers unable to provide pre-calving vaccinations, who cannot get the calf to suckle for the clostridial antibodies or who encounter an outbreak during calving, other options do exist to help provide immunity for baby calves.
The most recent development in BCV vaccinations for baby calves is Bovillis® Coronavirus from Merck. This new intranasal spray, modified-live vaccine is labeled for use in calves 3 days of age and older. Field trials have shown that it is safe for use in calves 1 day of age and older, and a single dose can reduce the duration and severity of enteric disease due to a BCV infection. Other options for calf vaccination include Calf-Guard® from Zoetis Animal Health and First Defense® from ImmuCell.
Ellis recommends that cattle producers work with their veterinarians to determine the optimum treatment options and cautiously read the labels on the vaccines because colostrum and age may interfere with the efficacy of the vaccine.
Other good prevention practices include managing a proper deworming program, reducing cattle stress, and using a good vaccination and backgrounding program. A combination of pre-calving and calf vaccinations can be used to prevent enteric disease from BCV, but there is not a vaccine on the market today that is labeled to prevent respiratory coronavirus in cattle, another reason Ellis emphasizes prevention by building strong immune systems for neonatal calves.
The goal is to support the immune system in every way possible so that if the calf encounters an infection or multiple infections they are best prepared to combat it and survive.
When treatable turns dangerous
“There’s work out there showing that calves are less likely to die from enteric disease if they are only dealing with 1 pathogen,” says Ellis. “If you go mixing pathogens including coronavirus, the mortality goes up. The theory is if you can prevent coronavirus, you can lower mortality even if the calves are dealing with other pathogens.”
No medications exist that will kill or treat a virus, so supported treatment is the best option for cattle that contract BCV. For enteric coronavirus, Ellis recommends preventing and treating dehydration to support the immune system in the best available methods. For cold winter months, it is important to keep the cows and calves out of blowing snow and muddy wet conditions when possible.
Although a widespread and persistent pathogen, BCV can actually be a virus that is relatively easy for cattle to handle. The danger of the virus comes from its ability to weaken the immune system, opening the door to a multitude of other pathogens that only worsen the problem. A multi-infection scenario, or an environment where calves are faced with external limiting factors such as weather, can cause enteric BCV, a relatively tolerable disease, to become life threatening.
More than just calf scours
The risk of BCV enteric infections can be managed and easily vaccinated against to provide protection. However, BCV respiratory infections present a more puzzling problem. Ellis says research indicates that BCV could be a contributing factor to a growing problem with BRD.
“I have taken deep intranasal swabs from central Texas origin, high-risk weaned calves getting ready to go to the feedyard and seen a very high percentage of PCR (polymerase chain reaction) tests show positive for BCV.”
Similar to its enteric counterpart, from a respiratory infection standpoint, BCV rarely causes mortality, but Ellis shares that it does set up the animal to be more susceptible to other killer pathogens.
Ellis says that in the future, if this infection can be addressed on the ranch level as it can with enteric infections, then the increased cases of BRD in the feedlot could be reduced. Unfortunately, the path to prevention is still a little unclear. As scientists seek a better understanding of BRD and BCV, Ellis predicts that the cow-calf producer may play an important role in reducing the number of future BCV infections and the effect of BRD on the cattle industry.
“Be aware of the emerging potential of this virus and the potential for it to be a contributing factor to the bovine respiratory disease complex,” says Ellis.
He encourages cattle producers to prepare for the threat of both enteric and respiratory BCV infections in their cattle and understand negative repercussions the virus could have on the herd as well as how to prevent loss.
“The biggest concern ranchers and cattle producers in Texas need to be aware of is that BCV can manifest itself early on in calf diarrhea and potentially as a respiratory virus in and around the time of weaning or comingling at a sale barn or feedlot,” says Ellis.
For producers who have had a disease outbreak in the past or if one strikes during calving season, Ellis says the first step is to contact your local veterinarian. BCV infections can be verified through PCR testing and the veterinarian can provide insight into the best plan of action for treating and preventing future outbreaks.
“If you suspect any issues with coronavirus contact your local vet and discuss the issue and then feel free to contact your Merck Animal Health representative or technical services veterinarian to get help with diagnostics,” says Ellis. “We’re always happy to help.”
“One Nasty Bug” is excerpted from the February 2017 issue of The Cattleman magazine.