American Fancy Rat & Mouse Association

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


Papilloma Wart Virus or Rat Pox Virus

Editor, Karen Robbins
Q A lady got rats from one of our breeders the end of December 2005 who developed sores on the top of two toes of their front feet. This lady also called me during this time (the rats developed sores a couple weeks after having them), and I told her to take them to a vet. They were in a wire cage, solid bottom, with wire ramps and shelves. It started out a small sore on the top of one toe on one rat. Then the toe next to it developed a sore (described as a small sore that scabbed up but wouldn’t heal). Later, the second rat developed a sore on the same initial toe as the first rat. They initially were using CareFRESH™ in the bottom of the cage, then took out all the bedding and were using a litter box and trying different beddings in it to try and potty train the rats to not go all over. When she first noticed the sore, she had been trying a bedding that I had never heard of, and I thought it might be a reaction to the litter—although just a sore on the top of one toe didn’t sound like a reaction—and suggested changing the bedding and taking them to a vet in a couple days if it didn’t get better on the normal bedding.

The vet cut off the wart/lesion on the first rat, cauterized it, and it appeared to have healed. The vet cut and cauterized the wart/ lesion on the second rat as well, and it remained a scab. They were told by a couple of doctors not to keep the rats. They were also told that rat pox can be transmitted to humans and that the rats got this problem from the mom rat which came from English stock. Later when she called to report an update (a biopsy they had done confirmed the rats had a virus and were told they would have to remove a toe to try and confirm just which kind of virus; vet had only seen those kinds of lesions in exotics at zoos; was narrowed down to Papilloma wart virus or Rat Pox virus; was told to keep children away from the rats until warts/lesions went away, wear latex gloves when around them, wait to see if gets better or worse), I asked her to send us the lab test results when she got them so we all could know what it was her rats had as I had never heard of anything like this. She never did send me or the breeder the lab results so we don’t know the official report on what the rats had. Another vet told her that although “Mouse Pox” is known to not cause problems in humans, there is a study from the Soviet Union where “Rat Pox” has shown to cause symptoms in humans—a rash on the hands and shoulders, and a cough, and advised to take another sample of the lesion (or amputate the toe) to see what those tests revealed.

Neither the breeder nor or I had anything like this in our ratteries so we are not sure it came from the breeder’s rats as suggested.

I would like any information on “rat pox” or the papilloma “wart” virus.

If it is papilloma virus, what do the lesions look like; how long does it take for them to show up; is this something mice can get/carry/pass on to rats and vice versa; is this something they can get then never get again and never pass on once they pass a certain point/time frame?

Answer by Ann Storey, MSc, FIBMS (a microbiologist), President N.F.R.S., England, and their genetic/medical expert.
A The rats most likely have papilloma (wart) virus. It is not contagious to humans. Some strains are very contagious to other rats. However, the condition is self limiting (they drop off in a few months), and the stud rapidly becomes immune, so that after a year or so you just don’t see it any more.

Turkmenia rat pox has not, as far as I am aware, been recognised out of Asia, where Turkemenistan and the surrounding countries is its natural home. An infected rodent was found in Kuwait. This disease is transmissable to man but is very rare. Rats can also contract cowpox (vaccinia) but this makes them very ill. This is transmissable from rats to humans but cowpox is not considered a serious disease in humans (it is used in the smallpox vacine).

Answer by Carmen Jane Booth, D.V.M., Ph.D.
A Basically there is insufficient clinical, macroscopic, or histologic information for me to be able to comment on what these rats may have had on their feet. The most common foot lesion in rats on wire bottom cages are related to trauma with secondary bacterial infection commonly from Staphylococcus bacteria. Papilloma viral infection (warts) would not be limited to the feet; however, solitary lesions do occur. The lesions are usually slow growing and there are no systemic symptoms. Papillomas from papilloma virus infection are not very common in pet or laboratory rats. Rat pox is a systemic disease and the rats would have been sick with other clinical signs. This virus is uncommon and not very likely. A skin scraping of the lesions may have yielded a diagnosis as there are inclusion in the skin cells in Pox viral lesions. Bacterial infection would likely have responded to a change of caging type, soft bedding, and topical/ systemic antibiotics.

Papilloma virus is the same virus that causes warts in humans, but the strains are different and they do not cross infect outside of experimental manipulation. Papilloma virus in rodents is very rare. A rodent can have a skin mass that looks like a papilloma but is not caused by a virus. These lesions are solitary and do not spread. Dogs, cows, rabbits, and humans have their own strains of papilloma virus and get lots of warts. Specific strains of human papilloma virus are directly associated with cervical cancer. Getting back to rodents, papilloma virus is extremely unlikely. There are so few cases reported and are historical in African soft-furred rat (also known as the Natal multimammate mouse/Natal multimammate rat, Mastomys natalensis) or European harvest mouse, not the Norway rat or domestic mouse (Mus musculus) that are in the pet or research trade. So, there is no published information on the latency to lesions, etc., or anything related to natural infection for that matter in rodents. The lesions in the rats were most likely bacterial and not viral.

Q Question about mice with “warts”: I have mice occasionally that get what looks like “warts” but never had anything in the rats. I had one “wart” sent in for tests years ago and it came back a squamous cell papilloma. I don’t know if this is what the mice are getting now. If a mouse gets one of these “warts,” the wart usually doesn’t grow or more develop. Only once or twice did one of these growths get bigger, and I euthanized the mouse though they act fine and act like it doesn’t bother them. I usually eliminate the mice from the colony when I see one has one of these. I hadn’t noticed any relation to the ones that get them from the ones that don’t (e.g. cagemates, siblings, kids, same color of mouse, etc.)—seems to be random. Is this anything I need to be concerned about and try and breed out or do something about? Karen Robbins

Answer by Carmen Jane Booth, D.V.M., Ph.D.
A No, you do not need to be concerned. Out of the 2,000 mice involved in my thesis, only one developed a squamous papilloma. This and yours are not due to mouse papilloma virus, but rather they are just a benign skin tumor. The term papilloma refers to any wart-like lesions and the virus was named after the appearance of the lesions in animals later found to be infected with virus later named papilloma virus. There is no reason to euthanize unless the animal is suffering. These are not contagious. There is a theory that mice have papilloma virus DNA incorporated into their DNA from millions of years ago, but no one is sure. A squamous cell papilloma is considered to be a benign tumor and squamous cell carcinoma the malignant counter part. *

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Updated March 19, 2014