Always have Rabies at the Top of Your List

D. E. Larsen, DVM

“We have a cow coming in this morning for Necropsy,” Dr. Norrdin said. “The ambulatory people have been treating this cow all week, and it died this morning.”

“It should be a good time for it, we don’t have anything in the cooler to work on,” I said.

“This cow died with neurological signs,” Dr. Norrdin said. “I want you guys to be thoughtful during this necropsy. Especially you, Larsen, when you remove the brain. Do you have any idea what I might be talking about.”

I had talked with a classmate earlier in the week about this cow. He was working on the ambulatory service this summer. Colorado State University had to scramble to keep students in the clinic during the summer months to keep up with the workload.

This cow had been looked at by two different clinicians and their students on multiple occasions. The cow suffered from a progressive neurological deterioration. People had their hands in the cow’s mouth and into the back of her throat, trying to ensure there was no foreign body causing some swallowing difficulties.

“What kind of a differential diagnosis list should you be working within your mind when treating a neurological case?” Dr. Norrdin asked.

I had been lax during the summer and was not used to coming up with immediate answers. This job was sort of one to do the manual labor of the necropsy room. It obviously provided a tremendous learning experience but from observation, not rote memory from a textbook.

“I guess viral encephalitis would be on the list, along with secondary bacterial meningitis from any of the respiratory viruses,” I said.

“You came close with your first guess,” Dr. Norrdin said. “You should always have rabies on your list. It should be at the top of your list, even though you will not see it often these days. The reason is that if you miss that diagnosis and fail to take care of yourself, you end up dead.”

“That is probably a good point,” I said.

“So be thoughtful, and work with your mouth closed today,” Dr. Norrdin said. “Hopefully, that will not be the diagnosis. If it is, we will have a mess. There have been over a dozen guys with their arms down this cow’s throat in the past week. The clinicians have really dropped the ball on this case.”

When the truck with the dead cow backed up the loading dock, we shackled the cow’s hock and picked her up with the hoist. This allowed us to move her on the track to the middle of the necropsy room floor.

We started the necropsy under the direct supervision of Dr. Norrdin. This was unusual in its self, we seldom had direct supervision at this stage. Dr. Norrdin was very worried about a possible rabies case, and he wanted to make sure everything was carefully documented.

When it came time to remove the head, I moved it to the butcher block in the middle of the room. I had become an expert at removing the brain from all the animals this summer. It was a skill that I would probably seldom use in practice, but I enjoyed being the best at something on the job.

With the skull on the table, I first had to remove the skin and soft tissue on the top half of the head. Then, with a large cleaver, I started shaving the bone from the skull to reveal the braincase. 

Once the braincase was exposed, the accuracy of my strokes with the cleaver became more critical. Finally, I would be able to lift the top of the skull cap and expose the brain covered by the meninges—those layers of tissues that become inflamed in meningitis.

There were several specific snips to be made to free the brain. Once this was done, I could lift the intact brain out of the skull and place it on the dissection table. Most of the time, I would slice the brain in a prescribed manner. In half, separating the right and left side. Then slice each side into quarter-inch slices, looking for any abnormalities. This time, Dr. Norrdin took over at this point. He did all the work on the brain and disappeared into the lab with the pieces.

There are several levels of diagnostic testing to confirm rabies as a diagnosis. The diagnosis of rabies is made in several ways. The one that is fastest and considered the most reliable, if present, is finding Negri bodies in the part of the brain called the hippocampus.

By the next day, rabies was a confirmed diagnosis in the cow. Most of us students had received several doses of rabies vaccine during our freshman year of school. Because of that previous vaccination and a positive titer, I only had to have a single booster vaccine. The students who had carelessly had the hands and arms in the cow’s mouth during the week preceding her death had to go through a complete series of vaccinations. 

That was a lesson well learned. But then, there is just a little more to the story.

A long year later, I was in Enumclaw Washington, ready to do a necropsy on a large dairy cow. Standing in the middle of the field, I sharpened my necropsy knife, the same one used to necropsy the rabid cow. As I stood there, the farmer had a whole list of questions. We stood and talked for some time. The entire time during this conversation, I continued to sharpen my knife on the wet stone.

Don’t allow anyone to tell you that a sharp knife never cuts you. After standing there sharpening my knife for 15 minutes, I lifted the hind leg of the dead cow and started the cut through the skin on her belly. This knife slid through the skin like it was butter. My stroke was so smooth, the knife flew through the prescribed cut, continued out into the air, and buried into the muscle of my lower left leg. Going into my leg a full inch. Ouch!

I stopped and put a wrap on the wound before preceding with the necropsy. By the time I was done, my left boot was sloshing with blood.

I did make a trip to the doctor’s office. We laughed at my careless actions and decided to leave the wound open. Antibiotics and a light wrap should take care of things.

Then I mentioned that I had done a necropsy on a rabid cow with this knife a little over a year ago.

“What do you think?” the doctor asked. “I would think that it would not be a problem at this point in time.”

“Will, the knife has been washed since then, but never autoclaved,” I said. “I would think that any virus on it would be long since dead.”

“I would think so also,” said the doctor.

“I am sure I still have a positive titer, just for insurance,” I said.

I did live, by the way.

Photo by Pixabay from Pexels