Rabies Virus

David E. Larsen, DVM

It was the best afternoon we had seen in some time. Colorado’s weather had taken a little getting used to, and the sunshine and warm temperatures this afternoon were a welcome relief.

Dr. Bass was shuffling papers at the podium in the auditorium as the class took our seats. Seats were not assigned, but as we started the spring quarter of our freshman year, everyone sat in the same seat that we started with in the fall.

“Today, we are going to dispense with any lecture, and you guys are going to go down to the Student Health Center and get your rabies vaccines. Veterinarians are high on the list of people exposed to the rabies virus in this country. This new vaccine, grown on duck eggs, provides excellent preexposure protection. It is given in three doses, three weeks apart. So, you can expect some escape from the classroom a couple more times this spring. There is no cost; they are using you guys as guinea pigs. But it is wise to take advantage of the opportunity.”

So we all marched down to the clinic in a formation that would make a drill sergeant shudder. There were eighty-four of us, so the line took a bit. 

***

The summer following my sophomore year of Veterinary school, I landed a job working in CSU Veterinary Hospital’s necropsy room. I spent the entire summer immersed in pathology. The work provided much-needed income but also provided me with the best learning experience I could have hoped to have.

I became somewhat of an expert at removing brains. I used a cleaver and could take a brain out of any animal in record time.

It was nearly mid-summer when Dr. Norriden came out on the necropsy floor. I pulled us all together for a little lecture. This was unusual for him.

“They are in the process of bringing cow around from the clinic shortly,” Dr. Norriden said. “This cow was treated by our ambulatory service about ten days ago. She was not diagnosed on the farm. On their initial exam, the cow had difficulty eating. They treated her several times, and things only got worse. They hospitalized her three days ago. In the hospital, they diagnosed a neurological disease, probably encephalitis.”

“Now, based on what I have just told you, are there any red flags here?” Dr. Norriden asked.

Bob, the pathology resident, looked around, waiting for one of us technicians to say something.

“Maybe rabies,” I said with little confidence in my choice.

“That’s the big thing,” Dr. Norriden said. “Anytime you deal with an undiagnosed neurological case, you should have rabies at the top of your list. You won’t see it often in your career, rabies is almost rare in our pet population due to the vaccination requirements. But this case is a good example. We will have a real mess if this cow is positive for rabies. The ambulatory crew and the hospital failed to have it on their list of possibilities. We have students who had their arms down this cow’s throat. When you take this brain out, Larsen, you work with your mouth closed. That is probably a good idea for everybody.”

It was not long before the cow was delivered to the necropsy room. Bob quickly examined the head and removed the tongue along with the esophagus and larynx. Then he severed the head and brought it over to the large chopping block for me to remove the brain.

I skinned the upper part of the head and then started removing the bone surrounding the brain. It was not long before I had the brain case exposed. Then, with careful strokes of the cleaver, I shaved the bone away from the underlying brain. A little work with scissors and I had the dura opened, and the brain was carefully lifted out of the brain case.

Dr. Norrdin was beside me as I lifted the brain. He took it from my gloved hands and disappeared into his lab/office.

The rest of the necropsy was unremarkable. The problem was in the central nervous system. Getting a good fixed slide under the microscope would take a day or two of processing. Then, if this was rabies, Dr. Norrdin could make the diagnosis by finding Negri Bodies in pyramidal cells of the hippocampus. Negri bodies are round or oval, sharply demarcated, eosinophilic inclusions within the cytoplasm of the infected neurons. They are considered the hallmark of rabies.

The following afternoon, Dr. Norrdin had the diagnosis. The cow was positive for rabies.

“The good thing is all of you guys have had your rabies vaccines, so you only need one booster,” Dr. Norrdin said. “Put this case in your memory bank. It will be unusual to see another one like this, but keep it in mind.”

***

“What do you think is going on, Doc?” Larry asked as we stood over a dead cow in his pasture.

“I don’t know,” I said. “But we will open her up and take a look.”

I had only been out of school for a few months, but my summer in the necropsy room gave me total confidence in doing a necropsy in the pasture.

Larry had a lot of questions. This was a big investment lying dead in front of us. We stood and talked as I sharpened my knife with a whetstone. By the time we were done talking, my knife was sharper than ever.

I leaned over the cow and inserted the knife under her skin in front of her udder. The knife slid through her skin with no resistance as I ran it forward. My stoke was firm and fast. The knife was so sharp it flew through the skin, and as my arm completed the stroke, it flew out of the skin and buried in the muscle of my lower leg.

“That was smart,” I said.

I took a moment and wrapped the wound on my leg. It was bleeding profusely. Then, I returned to my work on the cow. Once I had her belly and chest opened, the diagnosis was easy. A wire poked out of her reticulum, through her diaphragm, and into her heart.

“Hardware disease,” I said as I pulled the wire out to show Larry. 

We had a brief discussion, but I cut it short as I could hear the blood slouching in my boot.

“You can come to the office tomorrow, and I will review everything with you,” I said. “We will need to get some magnets for you for the rest of your cows. But, right now, I think I need to get my leg to the Doctor.”

The nurse at the Doctor’s office got me right into the treatment room when she heard the blood sloshing in my boot with every step.

The Doctor was quick to get the wound taken care of, and he chuckled at my story about how my knife came to be buried in my leg.

“There is one thing that worries me a little, Doc,” I said. “A little over a year ago, I used this knife to do a necropsy on a cow with rabies. This knife has been washed, but it has not been through an autoclave.”

“I don’t know,” the Doctor said. “You wouldn’t think the virus would survive that long, would you?”

We decided probably not, and besides, I had been vaccinated.

And I lived.

***

In Oregon, the reservoir for the rabies virus is in the bat population. Of the bats that are tested for rabies in Oregon, about ten percent are positive for rabies.

That does not reflect the incidence of the virus in the bat population because the only bats tested are those submitted by people of veterinarians.

In the early 1970s, rabies was significantly increased across the state, with several cases in pet dogs. This led the state to require rabies vaccination of dogs and to recommend vaccination for cats.

We held rabies clinics in public buildings for a few years. Rabies vaccines were given at near cost. I donated any profits to the humane society for providing labor in writing certificates. They were grueling events. I finally changed to doing the rabies vaccines in the clinic for a week at a reduced cost. That spread the numbers out, so it was such a pain.

Those vaccines solved the problem in the dog population and helped with the cat, but obviously, they did nothing for the bats.

As time passed, public health officials became strict about how they handled exposures or possible exposures.

Because a bat bite could be difficult to see or even feel in some cases, the rule evolved that a bat in a house with sleeping children was considered to have exposed those children to rabies unless the bat was captured and tested negative. The same went for pets in a house with a bat for any period of time. 

At first, it was recommended that unvaccinated pets in a house with a bat be euthanized. The other option was to quarantine the pet for six. Vaccinated pets could be given a booster vaccine for rabies, and they were considered okay.

It was about this time that I developed the philosophy that the rabies vaccine probably protected the pet from the system more than the disease.

In my years in Sweet Home, I had several rabid bats. One was found flopping around in the bathtub. Several were caught outside by cats, and a couple were captured flying around in the house.

In the 1970s and most of the 1980s, little attention was given to the finding of a rabid bat. But then there was a change in the state public health veterinarian. I don’t know if it was just that we were going follow the rules now or if it was a cover-your-butt type of thing, but the came about strict enforcement of the rules.

Sleeping children found in a house with a bat were considered exposed to rabies if the bat tested positive for the virus or if the bat escaped and was not tested. Pets were in the same boat.

Vaccinated pets were required to get a booster vaccination. Unvaccinated pets were scheduled for euthanasia. Their only other option was a six-month quarantine with vaccination at the end of the quarantine period. We were not allowed to vaccinate before the end of the quarantine period because the could influence the incubation period, which with rabies was known to be as long as six months.

Euthanasia was strongly recommended the the quarantine rules were arduous enough to make many people to go along with that recommendation. 

The reason for the increase in case follow-up was that the consequences for allowing an exposed pet to slip through the cracks would be the exposure of the owner and the public to a rabid animal and a possible human death from rabies.

***

“How long was the bat in the house?” I asked Lynn.

“We are not sure, but at least three days,” Lynn replied. “We saw it on Friday and then couldn’t find it. It finally came out on Monday. That is when Mike was able to swat it out of the air.”

“Are you sure you want to send this in?” I asked. “If it is positive for rabies, the public health folks will get involved. Boo’s rabies vaccine is not current. They will want to put him to sleep.”

“That doesn’t sound good, but I think we need to know,” Lynn said.

“Was there any human exposure?” I asked. “Did you or Mike handle this after it was swatted out of the air?”

“No, I just scooped it into this jar, and here we are,” Lynn said.

So, I boxed up the dead bat and sent it to the diagnostic lab at the vet school in Corvallis via our courier service.

Results came quickly, the next day in fact. The bat was positive for rabies. Within a few hours, I had a call from the state public health veterinarian.

“I have a report here that you submitted a bat for rabies testing, and the test was positive,” Dr. Van said.

“Yes, I got those results a little earlier today,” I said.

“Were any people exposed and kids in the house?” Dr. Van asked.

“No kids, the adults didn’t handle the bat,” I replied.

“What about pets?” Dr. Van asked. “And how long was the bat in the house?”

“There is one cat in the house, and the bat was in the house for at least three days,” I replied. “The cat’s rabies vaccine is a couple years out of date. I was hoping that a booster at this time would be adequate.”

“I’m sorry, but if the bat was in the house for three days, the chance of exposure for the cat is very high,” Dr. Van said. “A booster vaccine at this time would not be approved. Our recommendation is euthanasia for the cat.”

“I am pretty sure that this owner is not going to want to go that route,” I replied. “Is there an alternative for quarantine?”

“Yes, if they can do a six-month quarantine where the cat doesn’t leave the house, the rules allow that,” Dr. Van said. “Enforcement falls on your shoulders, Dr. Larsen. At the end of quarantine, you need to vaccinate the cat for rabies and send me a report. Any failure will result in forced euthanasia.”

“I think that is doable,” I said. “I will let the owner know.

So Lynn and Boo said through the quarantine, and I submitted the report along with a copy of the rabies certificate to Dr. Van.

***

Fast forward to the present day. 

Last year, my aortic heart valve went gunny bag. We had been watching it for the last six years, but it went from bad to worse in an acute episode. The Doctor thought I had had a heart attack, but it was just the heart valve.

During the two months that I was waiting for the replacement procedure, I had a conference with the main heart surgeon. He was explaining the procedure to me and the discussion involved the making of the new valve.

“This new valve is made from the pericardium of a cow,” the Doctor said. 

“So, what cat you tell me about the cow?” I asked. 

“What do you mean?” the Doctor asked.

“What about the history of the cow?” I asked. “I mean, I have known cows that wouldn’t their parts in my body.”

“I don’t understand your concern,” the Doctor said.

“If you look at my record, I’m a retired veterinarian, I worry about things like the rabies virus, among others,” I said. “A number of years ago, maybe twenty, a lady in Idaho died of rabies following a corneal transplant. When they investigated, they found the donor was a forest ranger who had died from an undiagnosed neurological disease.”

“I see,” the Doctor said. “All I can tell you is the tissue is treated in a manner that kills all the viruses and bacteria.”

“That sounds a little reassuring, but one day, you are going to have to worry about mad cow disease and those nasty prions that you can’t destroy, even with cremation,” I said.

“Thankfully, that is not a problem yet,” the Doctor said.

Photo Credit – John Torcasio on Pexels