American Fancy Rat & Mouse Association

This article is from the WSSF 2004 AFRMA Rat & Mouse Tales news-magazine.


Rat with Ear Lumps; Pimples on Rats’ Ears

By Carmen Jane Booth, D.V.M.

Rat with Ear Lumps

Janet Jeffs, U.K., e-mail
Q My name is Jan Jeffs and I am from the U.K. I have been keeping rats now for well over 20 years and have recently acquired a male Dumbo rat. He is only a couple of months old, but he has developed rather nasty hard lumps around and inside both of his ears. They seem to be getting bigger by the week, but at the moment he seems not to be bothered about it at all. I wondered if you would be kind enough to give me your opinion about what it could be and if you think it will be a problem in the future. I guess realistically there is not much a veterinary surgeon could do with a rat’s ears.

A This disease has been observed in several strains of rats and is known as Auricular Chondritis or inflammation of the cartilage of the ear. Nodular lesions are present in the pinnae of usually both ears as in this rat. The microscopic lesions are characterized by multiple nodules of macrophages admixed with destruction of the cartilage and infiltration of mesenchymal cells such as fibroblasts. There is also formation of cartilage nodules. Trauma and infectious agents have been considered as possible causes in the past; however, this disease is currently believed to be caused by problems with the immune system. There is no specific treatment for this condition and it is limited to the cartilage of the ears. There is no known cure. Treatment with drugs that affect the immune system could be tried or the pinnae amputated, but there is no published information on results after attempts at treatment. If the rat is not in pain, than doing nothing should be considered.

Percy and Barthold 1993, Pathology of Laboratory Rodents and Rabbits Iowa State University Press, p. 157.

Prieur DJ et al. “Auricular chondritis in fawn-hooded rats. A spontaneous disorder resembling that induced by immunization with type II collagen.” Am J Pathol. 1984 Jul;116(1):69-76.

Kitagaki M et al. “Auricular chondritis in young ear-tagged Crj:CD(SD)IGS rats.” Lab Anim. 2003 Jul;37(3):249-53.

Pimples on Rats’ Ears

From our files
Q Is it normal for ratties to have little pimple like things on their ears? I do not remember them having it when I first got them but maybe I was just not observant enough to notice it, so they might have had it when I bought them. I did not hold them or play with them for the first few days. I was letting them adjust to their new surroundings before I interacted with them. The rats are maybe 3 months old at the most. I have four rats—two males and two females. They were not sold as pet rats, they were feeders, and I am currently taming them down. They are out only with me and on me. I bought three of them at a pet store who on the phone said they had pet rats but when I got there they only had feeder rats. The older one my hubby got from a local pet store that sells older feeder rats but knew I wanted a rat and brought him home. He has been healthy but unfriendly. The little ones are the ones who have been getting sick. They (the little ones) currently have lice I believe, and I followed my vet’s recommendation to use kitten flea products on them to cure it—unknown if it has killed the lice or not yet.

Rat with Pimples
The white pimples on the edges of the ears.

One male and one female have the pimples on the ears, the other two are fine. They used to be cagemates, and I believe they are siblings, not positive though. It is only on the very edges of their ears. The right ear is way worse than the left on one of the rats. The lesions are not soft, they are hard and coarse to the touch, almost like warts. If the lesions are bacterial, then wouldn’t the other ratties have it as well? Or at least the other little rattie being that she is the only one of the three that I bought together that does not have it. The older male does not have it either but he is from a separate place altogether. I noticed it a couple days after I brought them home which is before I started using All Pet Pine bedding. (I was using aspen shavings which I did not like as it caused my ratties to sneeze excessively). There is no sneezing at all with the All Pet Pine. It is crumbled pellets of compressed pine that has all the bad stuff extracted out. It smells pretty good too and you can go in and scoop out the poop and stuff without having to remove the entire bedding. JT hasn’t sneezed since I changed over from aspen to this stuff.

I am feeding them all the rat and mouse pellets as well as what is called monkey chow and the rat and mouse mixture I got from the local pet stores that have the varied nuts and grains in it. They also get some treats such as Cheerios, pop corn, raisin bran, and crackers.

I use water and dish soap followed by a thorough rinsing to clean the cage out.

They just finished a course of antibiotics for upper respiratory infection. They were given Baytril two times a day for 5 days. The sneezing got better but I still heard a sneeze here and there until I switched over to All Pet Pine. I have not heard any sneezing since.

Where would I get some betadine?

What good is taking them to a vet if the vet has no clue about ratties and their care?

A I would suggest switching to a paper bedding until things resolve. For the lice, a kitten product should be okay, but I would use Ivermectin since it is quick, and you can eliminate everything with two doses exactly two weeks apart (200–400 microgram/kg body weight orally). All the rats should be treated. The cage cleaning is insufficient, and you need to use a 3% bleach solution followed by rinsing to really kill things. I would put any food in the freezer for 2 weeks before using. The important thing is cleaning up the environment to prevent reinfestation. A good pyrethrin-based flea spray with an insect growth hormone regulator should be safe and kill the eggs that may be in the carpet in your house.

Bacteria are everywhere and not all animals would have to have it. Also, if it is bacterial in cause, the strain may be resistant to the antibiotic (even Baytril). Also, it may need a longer course of treatment. Bacterial etiology pustules are not hard. There is a condition on rats where you get abnormal cartilage formation in the ears called Chondrodysplasia. If they do not resolve with medical therapy, then this may be what they are. There is no treatment, but they are not painful. Or, they could be warts (papillomas). Papillomas are caused by a papilloma virus and can spread. As far as the lesions on the ears, in the photos they look like small pustules. They are probably from a bacterial infection and need systemic and possibly topical antibiotics as well. I would guess that if the cause is bacterial, than Staph aureus is the culprit. Do the two animals with the lesions share the same cage? Do they fight? The only thing that I can suggest that might help is cleaning the affected areas with a dilute Betadine solution 2–3 times a day. If there is no improvement in 2–3 days, then they are going to need to be taken to the veterinarian. Remember, even Baytril does not eliminate Mycoplasma pulmonis completely.

Betadine is the trade name for iodine products. It or a generic version can be purchased from any pharmacy or drug store as it is an over-the-counter product. I dilute it to “tea colored.”

Be an assertive owner and tell the vet what you need to have done. If he/she does not have a clue and there are no other options, then you will unfortunately have to educate them on what is needed. What I tell people is this: You do not want to offend your vet, but make it clear that if they are unfamiliar with the diseases, conditions, and treatments of rodents, that you would like to work with them in the care of your rats because of the limited options where you live. Sadly, most veterinary schools do not cover rodent diseases or medicine, let alone how to handle them, etc. However, you may be better off trying to find a new graduate with an open mind and bring in information. There are web sites with information on the diseases of rodents. *

[Update: Ed. Note: Sarcoptes mites causes scabs on the ears.]

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Updated February 12, 2015