Malignant Catarrhal Fever

 D. E. Larsen, DVM

I stepped back from the chute to get a wider view of the cow. This was a sick cow. She was probably going to die. But what is going on with her?

“Bill, has this cow been anywhere other than here?” I asked. 

“No, she was born right here,” Bill said. “She hasn’t stepped off the place in her whole life.”

“I have only seen two cows that looked like this, and both were in school,” I said. “One had bluetongue, and the other had malignant catarrhal fever. Bluetongue is usually seen in sheep, but it can occur in cattle. I am not sure that it is seen in Oregon.”

“I haven’t heard of either of those, but they don’t sound good,” Bill said.

“I think it is more likely that she has a bad case of bovine virus diarrhea,” I said. “That is much more common, and I see a lot of it around here. But I haven’t seen a case of BVD that looked this bad.”

“What does all of that mean for the cow?” Bill asked.

“I think it means this cow is going to die,” I said. “Some cows will recover from BVD, and a few will recover from bluetongue, but the cows with MCF all die. My guess is this cow is going to die. Her eyes are both infected, making her blind. The mucus membranes in her mouth have many blisters and ulcers. It looks like the skin on her tongue is going to slough off. She has swollen lymph nodes and is draining mucus from her nose. She has a lot of trouble breathing, but I think most of that is upper airway issues.”

“Maybe we should just shoot the poor girl,” Bill said.

“That might be an option. There is really no effective treatment for any of this, especially MCF,” I said. “But the state will want a say in this case.”

“That doesn’t sound very good,” Bill said. “They will want me to spend a lot of money finding out what is wrong with my dead cow.”

“I think they are going to want to know what is wrong with her,” I said. “But, the testing they do will be at their expense. They won’t be asking you to pay for any of it.”

“What about my other cows?” Bill asked.

“We have talked about BVD before, and we did some vaccines last fall,” I said. “That distracts from that diagnosis, but some individuals will still contract the disease, even if they are vaccinated. Bluetongue is spread by biting flies and is considered to have no direct transmission. MCF is

spread from carrier animals, usually sheep, and infected cattle are not considered a source of infection to herd mates.”

“So is the state going show up with a bunch of vets, or what?” Bill asked.

“I don’t think that is going to happen,” I said. “I will collect some blood and some tissue from her mouth, which might be all they need. I will give you a call after I talk with them.”

After I collected the samples, I returned to the office and called Doctor White at the state veterinarian’s office. He was an assistant state veterinarian but much easier to work with than the other veterinarian in the office.

“Doc, I am pretty sure I looked at a cow with MCF today,” I said. “I collected some tissue off her tongue, some serum, and a purple top tube of blood that I can send to your lab. Are you going to want to look at this cow?”

“The only thing we worry about with MCF is making sure we are not dealing with a wildebeest strain,” Doctor White said. “What is the status of the cow?”

“She is pretty sick,” I said. “I think she will die in a day or two, maybe sooner. I didn’t treat her with anything. In school, I was always told it was a waste of time and money.”

“If she dies, just have the rendering company drop her off at OSU’s diagnostic lab for a necropsy,” Doctor White said. “I will call them so the rancher isn’t charged for anything.”

“So, this guy thinks that shooting her might be a good option,” I said. “I guess there is no problem with diagnosis if we do that.”

“Well, one disease they like to rule out is rabies,” Doctor White said. “Shooting her in the head might disrupt the tissues for that diagnosis.”

“That’s just great,” I said. “I never even considered rabies as a differential diagnosis. I was involved with a necropsy of a rabid cow when I was in school. We had a group of students and professors who had their hands and arms in the mouth of that cow. And I ended up getting some vaccines after that event. I think we will just wait for her to die. I doubt he will want to pay for a bottle of euthanasia solution.”

“Well, send me your samples, and send the cow to the diagnostic lab when she dies,” Doctor White said. “I will let you know about the diagnosis as soon as I have it.”

“The book says that there is no risk to the rest of the herd from this cow. Is that correct in your experience?” I asked.

“That’s correct,” Doctor White said. “This virus is probably carried by a sheep, and the sheep aren’t bothered. Transmission is somewhat of a mystery. It happens with direct contact but also from airborne transmission up to a few miles away. Don’t ask me how.”

“I don’t think there is a place in the valley where you can be over two miles from a sheep,” I said.

“Probably not, but the good thing is this a rare disease. If you see more than a couple of cases in your lifetime, that would be unusual.”

As soon as I finished my conversation with Doctor White, I called Bill to let him know the plan.

“She is going to make things easy for those state boys,” Bill said. “That cow fell over dead, not more than a half hour after you left.”

“Yes, that makes things easier,” I said. “We will call the rendering truck for you. They drop her off at the diagnostic lab in Corvallis. It might take a few days, but we should have a confirmed diagnosis.”

“What I don’t understand, Doc, is how the hell did she get this MCF stuff?” Bill asked. “I mean, she hasn’t left this place, and no new animals have come into the place in years.

“This virus is carried by sheep,” I said. “It doesn’t make the sheep sick. The book says it is transmitted by direct contact or through the air. They don’t know how it gets through the air, but it can travel a couple of miles.”

“Well, hell, there isn’t a place in this valley two miles away from some damn sheep,” Bill said. “What am I supposed to do about that.”

“It is rare, Bill,” I said. “Don’t lose any sleep over it. I will probably never see another case in my lifetime.”

***

The cow’s diagnosis was malignant catarrhal fever, and it was the usual sheep strain. I was relieved that the rabies virus was not involved.

Oddly enough, I did see another cow with MCF a couple of months later, about two miles down the road from Bill’s place. And there was a flock of sheep between the two places.

So I saw the cow in school and the two cases in Sweet Home. There was never another case. Three cases in a lifetime, all coming within a few years of each other.

Photo by Kris Rae Orlowski on Unsplash.

https://www.merckvetmanual.com/generalized-conditions/malignant-catarrhal-fever/malignant-catarrhal-fever-in-animals#v3275876