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Issue # 177 - December/January 2000

Dermatology Day at the country fair.

by Jon Geller

The steer in question was suffering from hypodermosis, or grubs. The third-stage larvae, now triumphantly exiting the skin, had started their journey about a year ago when a heel fly had deposited its eggs on the legs of the steer. From there the first - stage larvae penetrated the skin, using flesh-dissolving enzymes to tunnel their way to the esophagus, where they congregated for several months. The enterprising larvae then made their way to the tissues surrounding the spinal canal, where they enjoyed several more molts before emerging.

I was beginning my day as the on-site veterinarian for the Independence Day Stampede, a combination rodeo/county fair/4-H extravaganza, and was looking forward to seeing so many critters in one place for a change, instead of having to drive dozens of miles between farm calls, often desperately behind schedule.

My first order of business was to inform the owner of the steer that there was no risk to other animals or humans, since the emerging grubs simply fall to the ground to pupate for several months until a new heel fly emerges. Then I went about the somewhat grisly task of extracting the rest of the grubs. Using surgical tissue thumb forceps, I extracted 17 more grubs from their hiding places along the steer's back, after which I poured some disinfectant over the holes. Most large-herd domestic cattle are too wild for this treatment and must instead be treated with an insecticide.

Pesky -Parasites

Skin diseases caused by parasites are best prevented by treating animals in a herd before the life cycle of the unwelcome insect becomes established. In the case of cattle grubs, all animals should be treated as soon as possible following heel fly season, which in southern states occurs from January to March and in northern states from May to July. Small groups of individual cattle on the other hand, can be monitored more carefully and treated on an as-needed basis.

The list of parasites that cause skin diseases in animals is long, though lice and mites are the most common culprits. Most of these parasites cause hair loss, itching, redness, scaling and occasionally secondary infection. When more than one animal is affected, the possibility of parasites is greater.

The good news is that most can be recovered with a simple skin scraping. This should be done by a veterinarian. Often, there is zoonotic potential, meaning the parasite could infect humans. Always use gloves if you suspect parasites are present.

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