The Rat Fan Club

A Zoonotic Fungus Infection


by Debbie Ducommun


updated 6/27/17


I have heard from three rat owners who have experienced unusual skin lesions that were just like fungus lesions I have had many times. As it seems that most physicians are not familiar with this fungus, I thought it would be helpful to write an article about it.


The scientific name of the fungus is Trichophyton mentagraphytes. When you look it up online you will see that it is usually passed to humans from animals. The animals usually don’t have any symptoms. I have had both guinea pigs and rats four times I have had the skin lesions, but during a more recent occurance, I only had rats. For a while I wondered if I might be carrying the fungus dormant in my skin, but it never seems to occur in the same locations, but always somewhere new. I seem to be very susceptible to it. I’ve had it on many different parts of my body, including my upper lip, other places on my hand and arm, my chin, and even my butt!


The lesion starts out as a tiny sore red bump that looks much like the beginning of a pimple. This bump usually burns and itches. Within just a day or two, it becomes a blister, and then over the next day or two a cluster of blisters, and then one big blister. The blisters can itch or burn, and they are very tender and if you rub or bump them they hurt. Like most blisters, they eventually break open, but unlike most blisters, the fungus lesion can weep fluid copiously and continuously. The first time I had the fungus was several years ago on my forearm. I thought it was a spider bite and the blisters only got about a half inch across. After a few weeks the lesion went away on its own. About 3 years later I got it on my hand and this time I went to the doctor. I ended up going to two dermatologists, and the second one finally did a biopsy, which told us it was the fungus.



These pictures were taken on day 2 of a lesion on my forearm. I had starting putting the anti-fungal cream on it the first day, but didn’t realize the cream had expired a year earlier, so it didn’t help. This morning I bought a new tube of cream and have started applying it several times a day. At this point the blister burns pretty good all the time, and is starting to weep. While taking the pictures, I noticed the dark ring around the blister. I have never seen this before on any of my previous fungus lesions.


This was one of the first occurrences of the fungus on my hand, before I knew the best way to treat it.


Here is a lesion I developed on my finger on May 2, 2017.


If you don’t know what the lesion is, then it can get pretty bad before you start the right treatment. When I got it on my upper lip, and didn’t recognize it quickly enough, thought it was just a pimple, and it got awful! It spread pretty quickly and I had a miserable few days.  When I got it was on my chin, once again I thought it was just a pimple and didn’t recognize it for 4 days. I kept trying to squeeze the “pimple” and it got VERY inflamed and painful. When I finally realized what it was and started applying the antifungal cream, it started getting better right away. If you treat it right away it tends to clear up pretty quickly. What you want to use is an over-the-counter antifungal cream containing terbinafine hydrochloride. (I learned this from a study published online that tested the best of four antifungals to use.)  The last lesion I had on my hand was persistent and it didn’t go away completely until I also took oral grapefruit seed extract capsules (which is a great anti-fungal) for about 2 weeks. But that was before I knew the best type of anti-fungal to use. Back when my fungus was first diagnosed by the dermatologist he prescribed an oral anti-fungal medication but that didn’t seem to help much. (I don’t remember what it was.)


As for treating your rats, your only option is an oral treatment medication since you won’t see any skin lesions on them (I never saw anything on my rats or guinea pigs). I don’t know if an oral anti-fungal would actually eliminate the fungus on them since it didn’t work for me. You could try giving your rats the grapefruit seed extract. However, once you know what the fungus is, if you get a lesion you can treat it right away with the topical anti-fungal ointment, and if necessary the oral grapefruit seed extract capsules, and it should go away quickly. By treating it right away it is only a minor nuisance. It’s probably not worth treating your rats, and is certainly not a reason to get rid of your pets.


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