OPINION: Recent research says coronavirus can spread to cows’ lungs

Everyone is talking about COVID-19 right now — and I hope that everyone is safe. Other coronaviruses are relatively common as causes of diseases in livestock including cattle. We have known about some of them for a long time but we’ve learned more lately too.

In calves, bovine coronavirus is part of the neonatal diarrhea complex. It damages the lining of the intestines and shows up as scours in calves that are at least a week or so old. Coronavirus does not usually damage the intestines enough to kill calves — the loss of salts and fluids from the diarrhea is the greatest risk and is usually the major focus of treatment. Getting scours makes calves more susceptible to other problems like pneumonia though.

It also turns out that bovine coronaviruses can cause diarrhea in adult cows too, most notably housed dairy cows. It can cause the outbreaks known as winter dysentery. For a long time, we did know that coronavirus was involved even though we thought whatever caused it must be contagious because it often affects groups of cows. Even now, we are not really sure that the same exact coronavirus causes both winter dysentery and calf scours.

Over the last two decades, we started to find bovine coronavirus in calves with pneumonia. Naturally, people thought it was the same virus that causes diarrhea. Now it is clear that it is similar but not the same virus. There is not very good evidence that immunity to the coronavirus that causes scours will give any cross-protection against the coronavirus that causes pneumonia. Some of the first research looking at the bovine coronaviruses in pneumonia was in feedlot calves where pneumonia is one of the most common disease. Veterinarians would find coronavirus in calves that looked like they had common feedlot pneumonia (called BRD) but coronavirus also seemed to be a factor when there were sudden outbreaks of pneumonia too.

Fairly recent research in Canadian dairy calves has shown that coronaviruses are common in their lungs too. It is difficult to figure out how important they are in dairy calf pneumonia. Just because we can find a virus in sick cattle does not mean that the virus actually caused the illness. Some viruses are common but relatively harmless; other virus can normally be relatively harmless but become more dangerous when damage to lungs gives them an advantage. It looks like that’s how many bacteria cause pneumonia — they gain an advantage when the airways are damaged or overwhelmed. This is partly why tests collected from sick animals are so difficult to interpret.

Both of the coronaviruses that cause scours and the coronavirus that are linked to pneumonia seem to be very common – it is likely that you could find them in most, if not all, dairy and beef herds.

It is always better to prevent disease, especially diseases caused by viruses, than to try to deal with them once calves get sick. Most of the preventive steps for diarrhea are not specific to coronaviruses. They involve limiting exposure though housing and sanitation and making sure calves are well-fed and managed to maximize their own resistance (called ‘innate immunity’). Good colostrum management is essential. There are vaccines that can be given to cows so they pass on immunity through colostrum.
There are also vaccines that can be given to calves themselves. There isn’t good scientific evidence that scours vaccines give protection against the coronaviruses that are linked to pneumonia.