American Fancy Rat & Mouse Association

This article is from the Winter 1998 AFRMA Rat & Mouse Tales news-magazine.


Longevity Study; Update: Scabs...Diet or ???; Ivermectin Treatment for Pinworms

By Carmen Jane Booth, D.V.M.

Longevity Study

Carmen Jane Booth, D.V.M.
Q Question to the AFRMA Membership: To the nearest month, what is the oldest documented or estimated rat or mouse that you have ever had. My oldest was around 3 years. Please send your responses to the editor and I will compile them and publish the results in a subsequent newsletter. I have been reading articles on aging in rodents and am interested in seeing how or if our pet rodents differ.

NEWSLETTER UPDATE Re: Scabs . . . Diet or ????? by Nichole Royer


Q Is it possible that some rats become more sensitive to some sort of mite or lice bite when they are fed high protein/fat foods? If some sort of parasite is involved, why haven’t any of my other rats shown signs of it? Why do other treatments for parasites like powdering, dipping, spraying, and bathing with flea products not have any affect on this condition, but Ivomec does? Why does this condition appear to be passed from father to son, and why does it usually only affect males? Why does it usually first appear when the rat reaches maturity (6 months) and then flare up again at 2 years? I would like to find the answers to these questions, and am very interested to hear from anyone else who has had similar results when treating with Ivomec, and particularly from anyone who Ivomec has not helped. Could rats have the same type allergies to corn as dogs do, and that be a contributing factor. What are the best ways to treat, other than taking away the corn in the diet and giving cortisone, etc.?

Answer: Comments on Scabs, Diet or ??? by Carmen Jane Booth, D.V.M.
All treatment of your animals should be done under the supervision of a knowledgeable veterinarian.

AI am unaware of any reports of rats having allergies from corn. Dogs and humans are very different from rodents regarding allergies. Most often, the skin problems that rodents experience are from the bedding material itself or external parasites, rather than from the diet.

If sufficient time has passed after all environmental factors (caging, bedding material, external parasites, etc.) have been removed or changed and the problem has not resolved with Ivermectin treatment, I would first suggest trying a short course of antibiotics to rule out a bacterial etiology (cause). Following this, if the rat still had problems, and the owner wanted to pursue an allergic etiology, then I would recommend feeding one of the hypo-allergenic dry dog food diets for 6 weeks. If improvement was noted, then I would slowly add in additional fruits, vegetables, and starches. I am a proponent of feeding rodents a mixed diet, based on either a high-quality rodent block or dog food (if no block is available), in combination with washed fruits, vegetables, and starches.

Using a combination of antibiotics and anti-inflammatory steroids, such as the tetracycline and hydrocortisone spray that Nichole used for refractory (difficult) skin problems, can be extremely useful but are not without their risks. I would imagine that the spray is intended for dogs with “Hot Spots” from chewing themselves because of fleas. Anti-inflammatory steroids are extremely potent and powerful medications, and they are used extensively in veterinary medicine for itching related to allergies or hypersensitivity. Unfortunately they do not eliminate the underlying cause of the itching and can make the problem worse.

Anti-inflammatory steroids are absorbed systematically through the skin and there are risks associated with them. In general, if an animal is otherwise healthy, a few applications will probably not cause any problems. The exact mechanisms whereby steroids act are unknown, but it is clear that they suppress, but do not abolish most, and possibly all aspects of acute and chronic inflammatory processes. The side effects that may occur during treatment are related to the physiological effects. Some of the side effects include: increased water consumption (polydipsia), increased urination (polyuria), muscle wasting from protein catabolism, delayed wound healing, osteoporosis (decreased bone mass), bone fractures, increased appetite, and a decreased ability to fight off disease. Animals that are on chronic (long term) steroids, are particularly vulnerable to stress if treatment is terminated abruptly. Anti-inflammatory steroid treatment is palliative (provides relief), but not curative. Steroids are extremely useful, but should be used with care and under the direction of a veterinarian.

Regarding the use of Ivermectin:

In most cases of pruritus in pet rodents, the mite is not observed, even with repeated skin scrapings. Ivermectin and flea sprays are completely different in their site and mechanism of action. With Ivermectin, once the louse life cycle is broken and there is no new infestation, then the problem (pruritus) is usually resolved. From what you describe, the pruritus in your rats was most likely due to mites, and unrelated to diet. The infestation probably came from the bedding material. As far as your other concerns regarding the increased frequency in males and uneven distribution of affected animals, there is insufficient information for me make any definitive conclusions. With older animals, they may have an underlying problem that may make them more susceptible to other diseases like lice. Please note that Ivermectin has been proven to be extremely toxic to nursing animals.

Following is a reprint of the article that appeared in the Medical section of the Spring ’97 newsletter.

Ivermectin Treatment for Pinworms

An Oral Ivermectin Regimen That Eradicates Pinworms (Syphacia spp.) in Laboratory Rats and Mice. Klement et al. 1996. Laboratory Animal Science, 46:3 pp. 286-289.

Ivermectin Dose

The daily water intake for 10 rats (five of each sex) ranging in weight from 160 to 658 grams and 10 mice (five of each sex) ranging in weight from 19 to 23 grams was determined over a 7-day period. Mean daily water intake was 116 microliters per gram body weight and 505 microliters per gram body weight for rats and mice respectively. (Mice have a higher metabolic rate than rats because of their smaller size.) Based on the water intake, rats were given 25 mg of ivermectin (2.5 ml of Eqvalan) diluted in 1 L of drinking water, while the mice were given 8 mg of ivermectin per L of drinking water. Water bottles were shaken daily.

Treatment Protocol

There were 5 different treatment schedules as follows:

  1. No treatment (control).
  2. Two courses of ivermectin on days 1 to 4 and days 8 to 11.
  3. Three courses of ivermectin on days 1 to 4, 8 to 11, and 15 to 18.
  4. Four courses of ivermectin on days 1 to 4, 8 to 11, 15 to 18, 22 to 25.
  5. Five courses of ivermectin on days 1 to 4, 8 to 11, 15 to 18, 22 to 25, and 29 to 32.


Ten rats and five mice naturally infected with pinworms were in each group. There were an additional 30 rats in group 3.

Detection of infection:

All rodents were followed for 29 to 32 weeks after treatment was stopped by perianal impression with cellophane tape at weekly intervals. Any animals that died or were acutely ill were necropsied. Any treated rodent that tested positive for pinworms after completing the treatment period but before the end of the follow up period was euthanized and necropsied. At the end of the follow-up period of study, all rodents were euthanized and necropsied.


Cages, bedding, and water were changed twice a week. Filter top cages or special decontamination procedures to prevent cage-to-cage transmission were not used.


All rodents given either a 4 or 5 course treatment of ivermectin were negative for pinworm ova over the entire 29 to 30 week follow-up treatment period. A number of animals died from unrelated causes in both the control and treatment groups. The mortality was similar between the controls and treated animals and probably reflects the fact that the animals consisted of elderly, retired breeding animals with other chronic diseases.

Additional Comments from Dr. Booth

The Eqvalan brand of ivermectin was used, in contrast to the Ivomec brand of ivermectin, because it is readily soluble in water and does not precipitate out of solution.

No pregnant or lactating females with pups were used as ivermectin accumulates in the milk and newborn rodents are highly susceptible to its neurotoxic effects.

Since ivermectin has no activity against pinworm ova (eggs) which survive for prolonged periods off the animal, the authors wanted to determine how many repeated treatments were needed to keep the rodents worm-free until all the ova had died or matured into adult worms and were susceptible to ivermectin.

Since cellophane tape tests are not entirely reliable and can be negative in heavily infected rodents, a complete necropsy with evaluation of cecal and colon contents for adult pinworms was necessary to confirm their complete eradication from ivermectin treatment. *

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Updated April 7, 2014