This article is from the Nov./Dec. 1996 AFRMA Rat & Mouse Tales news-magazine.

By Carmen Jane Booth, D.V.M.

From our files
Q I’ve seen some information written about abscesses. But I’d really like to know more about them. What if there never was a scratch or sore? What would make them develop? If it’s only under the skin, should the muscle be cut, “To make sure it isn’t any deeper”?

Also, I’ve just learned about a disease/infection called “bumble foot.” It causes sores on the back feet. Can you tell me anything about this?

A An abscess is defined as a localized collection of pus buried in tissues, organs, or confined spaces. Most of the time we see them as a bump or soft swelling under the skin. Pus is basically made up of neutrophils (one of the 5 white blood cells circulating throughout our body) and dead (necrotic) cellular debris. One of a neutrophils’ main function is to kill bacteria. A skin abscess is formed when bacteria or a foreign body (splinter, etc.) penetrate the skin through a puncture, abrasion, bite, or scratch. In many cases, the skin wound has healed by the time an abscess is seen.

Each different type of bacteria has a minimum time (lag phase) before they can replicate into two bacteria. As soon as neutrophils find bacteria, they recruit more neutrophils and other white blood cells by releasing special substances called chemoattractants. In the process of killing the bacteria, many neutrophils die and this results in the release of many other biologically active products that result in swelling, redness, etc. Additionally, many of the products that the bacteria release cause tissue damage as well. As the number of white blood cells increase, along with the influx of fluid and damage to the tissue, the area swells and you now have a visible abscess.

In mice, abscesses are more common in males than females, because they fight more. Bumble foot is just the lay person’s term for abscesses seen on the feet of mice. Bacteria are everywhere in the environment and if the surface that the animal walks on is too rough, then foot abscesses occur. This is a big problem in rabbits and guinea pigs.

Treatment in general, consists of systemic antibiotics (usually orally), and cleaning out the wound. In many cases, simply hot packing the abscess with a warm wash cloth and soaking with dilute betadine solution while the animal is on antibiotics will cause the abscess to rupture so that the body can heal properly. If there is extensive tissue damage, then the animal has to be anesthetized and the area debrided (all the necrotic tissue removed) and sutured. Foot abscesses are problematic in rodents, because there is not much tissue to work with. In these cases, antibiotics and cleaning the feet has to suffice.

In dogs and cats in California, fox tails are the leading cause of abscesses.

From our files
Q Is there any kind of pain medication that is safe to give to rats? If so, in what doses? Do you have any updates on pain medicines for rodents from what has been printed?

A Cortisone is an anti-inflammatory steroid that has been reported to give a feeling of well-being in humans at high doses where it causes immune suppression necessary in certain diseases. When inflammation is the cause of pain or discomfort, then anti-inflammatory steroids may help alleviate pain by reducing the amount of inflammation. Steroids have no direct pain relieving properties.

There are no non-prescription pain relieving products that would be effective in rodents. Many of the lectures that I have attended at different meetings suggest that with the high metabolic rate of rodents, most pain relieving drugs are metabolized so quickly that the frequency of dosing required makes it difficult to provide sustained relief.

Q I’ve heard of some debate over using chloroform to euthanize rats. Is it bad to use, if so, why, what does it do to the animal, and what is the better alternative if it shouldn’t be used. What do you recommend if a person can’t get to the vet to euthanize a rat or mouse?

A The reason that chloroform is not recommended is because it is extremely carcinogenic to people if you get it on your skin or breathe it. In industry, it can be used safely inside a biosafety cabinet, or chemical fume hood. The animal does not suffer with its use. However, because is a dangerous chemical, the humane method of euthanasia recommended by the American Veterinary Medical Association’s Panel on Euthanasia, is carbon dioxide. Canisters of CO₂ are not expensive, and there are aquarium-type chambers where you fill the chamber with the gas and place the animal in the chamber. The animal loses consciousness and dies. There is no pain involved. Additionally Dry Ice (frozen CO₂) can be used, as long as the animal does not come into direct contact with the ice. I have seen people place 2–3 inches of crumpled paper towels over the dry ice which is in an insulated bucket. Proper safety methods to avoid freezing injury must be taken.

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