This article is from the WSSF 2007 AFRMA Rat & Mouse Tales news-magazine.

By Carmen Jane Booth, D.V.M., Ph.D.

Karen Robbins
Q I came across this when I was looking at a pet rat site, that you can use Ivermectin to treat ringworm. In what you had written about ringworm on rats and mice (www.afrma.org/med_ringworm.htm and www.afrma.org/ med_ringwormmice.htm) and the Merck Vet site, Ivermectin is not a treatment—ringworm is a fungus and Ivermectin is used to treat parasites.

My question therefore: Is there anything in Ivermectin that would help in the treatment of ringworm? One question that had brought up my discovery of this statement on the pet site, was one of our members had a litter of rats (6 weeks old) that he brought by for me to look at. One had what looked like a “chewed” strip of fur about ½ inch wide and about 2 inches long on its side that looked like this rat or one of the siblings or perhaps mom had barbered (chewed the fur off). There were no scabby areas. We didn’t think anything of this though I thought it strange that only this rat had any missing fur patch. Later, this rat and others went to their new homes. However, the patch got bigger and another in the litter was showing a bare area (not circular). The breeder took one of his to the vet that was showing a problem. The vet did the ultraviolet light but was inconclusive as to if it was ringworm. No other tests were done (skin scraping, fungal test, pluck fur and look under microscope to look for parasites). They were sent home to treat for mites with a paste wormer (rice-size piece—told to be careful on amount given). I suggested using the Ivermectin if it was “mites” as this is safer (I’ve heard of too many people killing their rats by using the paste wormers). They reported: “The rats are recovering nicely (slowly, but surely). It never spread to any of the other rats, or the mice, but we’re still treating everyone. It’s weird, only babies from one litter were effected (even though we combined three litters with each other, and some with other adults). Maybe we caught it and started treatment before it could spread)” and “They’ve been on treatment/medication for 3½ weeks, and there haven’t been any new breakouts since treatment started.” [Update: they also got medication to treat for possible ringworm.]

Does this sound like ringworm or some kind of mite/lice?

A Without a skin scraping or culture to confirm that it was the fungus commonly called ringworm or visible mites on the fur, you just can’t know what the problem was. It could have been mites and it is common not to find them unless the number is high on the animal.

Ivermectin has no activity against fungi and if giving it improved the skin in some rodents, than they probably had an underlying parasitic infection (mites) and not a fungal infection.