Consider upstream factors when investigating disease

The other day, I presented a case of a deceased wolf to the veterinary students’ pathology rounds. This is a weekly event at the University of Calgary where veterinary pathologists take turns showing and discussing interesting cases to create a less formal learning experience for the students in the program.

Like many things this year, rounds have gone online so I took the opportunity to rummage through my photo archive for old cases that might be of interest. Buried deep was a striking set of pictures of a wild grey wolf.

The first picture is a close up of the wolf’s face, which has been stabbed by several hundred protruding porcupine quills. It must have bit down hard and had a ferocious battle with the porcupine, since quills were embedded deep in the lips, tongue, roof of the mouth and muzzle.

The next photo in the set shows a wider view of the animal, the ribs protrude sharply with no visible body fat left. This animal had starved to death.

The simple sequence of events isn’t difficult to reconstruct. The wolf aggressively attacked the porcupine, embedding a massive number of quills in its face and mouth. With the quills in place, it was unable to hunt and died from starvation.

But wait a second, I told the students. Aren’t wolves among the smartest of wild animals? After all, they are the ancestors to border collies. Surely a wolf should know better.

Maybe it was simply a case of a wolf making a poor life choice. But it is important to think about upstream causes of illness and death as well.

In this instance, the wolf may have had worn teeth and been unable to hunt larger prey. Out of desperate hunger, it attacked the porcupine, even though it may have known better. Or perhaps it was infected with a virus that alters its behaviour by damaging the brain. Rabies virus is a top candidate, but canine distemper should also be considered. Both viruses are part of routine vaccinations for our domestic dogs, but wild wolves don’t have this luxury of protection. Both viruses are worth considering as an upstream cause of this wolf’s death.

There are also downstream effects from the obvious events that transpired when the animal died. The wolf appears to have starved to death. But the hundreds of quills did significant damage to the skin. The many small wounds would give bacteria an opening to cause an infection. With time, the bacteria may have spread, leading to a bloodstream bacterial infection. It is entirely possible that an infection combined with lack of food ultimately did in this poor wolf.

My intention was to use this case to emphasize to the students the importance of looking beyond the obvious in cases of animal illness or death.

We use the scientific terminology “proximate cause” to refer to the factor immediately responsible (the porcupine quills leading to starvation in our wolf case). But we shouldn’t miss the opportunity to consider the “ultimate causes” as well, which are upstream factors (an underlying disease or poor teeth in the wolf case).

On farm, thinking about these ultimate upstream factors can be helpful for taking preventive measures and deciding on optimum management beyond the immediately obvious disease processes.

For example, micromineral deficiencies, subclinical viruses such as bovine viral diarrhea virus in cattle, stress from handling, mixing groups and shipping, limited genetic pool and weather can all impact the manifestation of illness in our herds and flocks.

My point in relaying this story is to highlight the importance of thinking broadly about illness and disease, no matter what species of animal is affected. While the obvious cause of death or illness in a flock or herd may be apparent, it is good to ask, is that all that is going on?

Dr. Jamie Rothenburger, DVM, MVetSc,PhD, DACVP, is a veterinarian who practices pathology and is an assistant professor at the University of Calgary’s Faculty of Veterinary Medicine. Twitter: @JRothenburger

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