American Fancy Rat & Mouse Association

This article is from the Fall 2003 AFRMA Rat & Mouse Tales news-magazine.


Rolling Mice; Rat/Mouse Health Questions; Theiler’s Murine Encephalomyelitis Virus (TMEV)

By Carmen Jane Booth, D.V.M.

Rolling Mice

Ronny Sugarman, Red Headed Mousery, Denver, CO
Baytril was the choice of two highly qualified small animal veterinarians. I have got an “opinion” from one person who thinks baby Amoxicillin is the cure for everything. Both vets listed in my story told me hands down that baby Amoxicillin can do nothing for the rolling condition, viral meningitis, because it is not bacterial. My vets have both treated other mice and rats with Baytril with a high success rate. I wrote this to help others with the same problem. I hope it helps.

My experience with Baytril

I am excited to be a new member of AFRMA. My favorite colors in mice are red, strawberry blonds, and blonds. I fell in love with wild mice after 9-11-01, but that’s another story for another time. By May 30, 2002, I purchased my first pet mice. Two of my red mice came down with wry neck or what I call “The rolling disease” or viral meningitis where mice roll and roll and can’t stop. Crimson was the first one. I pulled her out of the aquarium and held her by the base of her tail, in my palm, so she could not roll, and called my vet. She immediately prescribed 0.15mg of Baytril. I held her for 5½ hours (massaging also helps). I put her back in the aquarium in an upside down wooden hut lined with aspen chips. Within 4 days, she was back to her frolicking self. I kept her on Baytril for 2 weeks with no ill effects.

A few months later, Li’l Red, my Red Satin mouse, came down with the same virus (both mice came from the same place). I proceeded with the same treatment but I believe the virus had mutated as it took a lot longer for her to recover. She was on the Baytril for 9 weeks and still slightly tipped. Once I did some research and found out I could use the two drugs together, I used Baytril in conjunction with baby Amoxicillin for 7 days, and something unexpected happened. Li’l Red was a dwarf mouse about one-third smaller than the other mice. When I put her on the two drugs for 7 days she lengthened! She is now the same size as my other mice. Quite an exciting development! The dosage on the meds is Baytril 22 or rather 22.7 22mg/m 2.5ml. The dose is 0.15 1x a day. Li’l Red went up to 0.20 a day. However, each animal is different. When I tried to give her 0.10 2x a day, she got violent nosebleeds. So I tried 0.20 1x a day, and the nosebleeds went away. I was also giving them Strawberry Ensure or “nummies” as it’s known around here and they had some hair loss so I give it as a supplement or a treat, but keep them on a balanced diet. This is good news for mouse and rat breeders alike. The “Rolling Disease” no longer means death to mice and rats. So mouse and rat owners need not despair. There is help out there in the form of Baytril.

I suspect it is a virus that mutated, as Li’l Red did not respond to either Baytil or Baby Amoxicillin. If Baytril or baby Amoxicillin don’t stop or completely heal the “Rolling Disease” within 4 days, it is probably Viral Meningitis. The next step is Acyclovir 400mg. The dose is 0.05cc 1x a day for 10 or 20 days, or as long as needed though I tried it with weak results.

My vet then put Li’l Red on Tibrissen after the Acyclovir did only a little for her. The Tribrissen is having a lot bigger impact. Then my vet suggested Tribrissen Dose 15mg per kg. On the bottle is says SMZ-TMP 120 mg. Li’l Red has been struggling with this a LONG time, but since the Tribrissen (which goes into the brain better according to my vet Dr. Jerry Koster (Cherrelyn Animal Clinic, Englewood, Colorado) Li’l Red is acting like a “pup” bouncing on wheels, etc.

My vet also gave me a great ointment for sores and cuts, C.G.B. Ointment (Tri-Otic) 7.5ml 2x a day.

Q A question I had was how many days do you use baby Amoxicillin and do you use it 1x or 2x a day? What dose? This is for mice. I was told 3 days only, and I was told it is safer to use baby Amoxicillin than Baytril on pregnant, nursing mums, and babies, but the Batril on other mice is quicker, stronger. My experience with Baytril backs this up.

Rat/Mouse Health Questions

Andria Manecke, Cut Bank, MT
Q I’ve owned rats and mice for over 20 years, and have never seen anything like this. I’m having trouble finding reference materials that cover rat and/or mouse diseases in depth, and my vet doesn’t have a clue.

Okay, to start with, I had two solid black male pet rats. They lived to be close to 3 years old before developing health problems. At the time, I assumed these problems were entirely age-related. One rat developed a large abdominal tumor. No other problems with him. The second became paralyzed in one hind leg. Gradually, over the course of about two months, the paralysis got worse, and spread until one entire side of his body was paralyzed. As a result, he would drag himself along with the healthy side, causing him to “roll” wherever he wanted to go. He did not appear to be in any pain, and could eat and drink, so I didn’t rush to have him put to sleep. However, one day I noticed that one side of his head, around his eye, was badly swollen. It quickly got worse (over the course of a few hours) so that his eye bulged out, and then appeared to “pop.” The eye was ruined. At that point, I decided to have the rats put to sleep, as they were both old and obviously suffering.

My vet humanely euthanized the two rats. Shortly thereafter, I obtained three Siamese-colored mice from a local pet store. I cleaned the old rat cage thoroughly with soap and water, but didn’t disinfect it (stupid, I know, but I honestly thought I was dealing with an age-related problem, and not a contagious one, with my rats), and placed the mice in the cage. Shortly thereafter, two of the three mice developed serious health problems. The third remains, to this day, healthy. The first mouse developed a swollen head and eye, identical to the rat. The eye bulged out, weeped badly, and became opaque. I administered tetracycline to him, and gradually the inflamation left and he now appears perfectly normal, but blind in one eye (the eye is intact, but opaque-colored). The second mouse became paralyzed in one hind leg. No eye problems, but the paralysis was identical to that of the rat, and occurred very soon after I got her. She has now, a few months later, become nearly as bad as the rat had been, almost entirely paralyzed on one side of her body, and although she doesn’t roll, she does move very “crooked” and is using only one side of her body.

I have since acquired five additional mice. Although they are not housed with the “sick” mice, they are in the same room. None of them have developed any unusual symptoms. The only thing I can say with any certainty about the two sick mice is that they are very inbred. Whether or not this made them more susceptible to whatever the sick rat had, I don’t know. Why the third mouse (not as inbred, but likely inbred as well) didn’t get sick, I have no idea.

I discussed this with my vet, who at first dismissed it as “coincidence,” but then, upon examining the mice, decided it certainly was identical to the rat he had put to sleep and was probably infectious. Oh, one other thing, the female (paralyzed) has never produced a litter…I am assuming this has affected the fertility of either, or both, mice. The third, otherwise healthy female, also has not produced a litter. I did also discuss this at length with the pet shop owner, who raised these mice. She assured me her mice were completely healthy, and said she was absolutely certain that my rat, and my mice, were suffering from injuries. The cage in question is a 20-gallon aquarium with a fine mesh lid. They have a lightweight plastic water bottle in their cage, and various soft cardboard objects…I can’t imagine how they could’ve been injured. My vet disagreed with the injury diagnosis, as well.

I’ve tried to provide you with as much information as I can recall. Any idea what I’m dealing with? Should the sick mice be destroyed to prevent the further spread of it? Should all of the mice be destroyed? Should I start over from scratch, with new mice from a different breeder? I don’t know what to do. These mice are my pets, and I am very fond of them, but unless I can figure out what I’m dealing with here, I’m not terribly comfortable keeping them. I certainly cannot bring home any new animals with them here, unless I can figure out what I’m dealing with and how to treat it. I’m baffled. Any advice/help you could provide would be greatly, greatly appreciated.

Thanks for your time.

Carmen’s answer to both questions
A Mice and rats with the clinical symptoms of a mild head-tilt or severe involvement of the middle ear expressed as circling or rolling can be the result of any number of different bacteria and uncommonly from Theiler’s Murine Encephalomyelitis Virus.

The number one agent responsible for almost all clinical symptoms seen in pet rats and mice is Mycoplasma sp. This bacterium is ubiquitous in pet rodents. Infection of the middle ear (otitis media) is a frequent manifestation of murine mycoplasmosis. Culture of nasopharyngeal flushing and serology are the most common diagnostic tests used to confirm the disease. Any clinic can take a radiograph with their X-Ray machine to confirm involvement of the middle ear. The tympanic bullae are usually opaque rather than clear. Infection of the middle ear by other bacteria can result in the same clinical symptoms, one I personally confirmed in mice with otitis media is the bacteria, Pseudomonas aeruginosa.


In any bacterial infection, the treatment of choice is antibiotic therapy. However, since Mycoplasmas sp. are difficult if not impossible to eradicate completely and re-exposure is likely, chronic antibiotic treatment is often needed to keep the clinical signs in check. If the damage to the structures of the middle ear are severe enough, antibiotic therapy may stop the progression of the changes, but the damage is irreversible and the clinical symptoms may persist. There are many different antibiotics that one can use to treat bacterial infections. For Mycoplasma infections, Baytril tends to be the antibiotic of choice among many veterinarians. Other antibiotics can be effective with chronic therapy; but Baytril tends to have the highest success rate. However, since it has been used for quite a few years now, bacterial resistance by some strains of Mycoplasma sp. is inevitable.

Strain differences:

The most common species of Mycoplasma that causes disease is Myocplasma pulmonis. Mycoplasma arthritidis and Mycoplasma colitis are not considered to be significant natural pathogens. Another strain of Mycoplasma, M. neurolyticum is the causative agent of “rolling disease.” However, neurologic symptoms have only been reported in experimental inoculation as a result of the exotoxin released by this bacteria. In published reports, this strain of Mycoplasma is relatively nonpathogenic under most conditions.

Previous articles give detailed information on Murine Mycoplasmosis.

Theiler’s Murine Encephalomyelitis Virus (TMEV)

This is the one infectious agent that is considered primary pathogens of the central nervous system in rats and mice. It resembles poliomyelitis virus infection of humans. TMEV is a RNA virus of the family Picornaviridae, genus Enterovirus. Natural infection is usually inapparent with less virulent strains. Clinical disease is uncommon; however, in virulent strains they may be severe. In less virulent strains clinical signs include: flaccid paralysis of one or both rear legs, but otherwise they appear normal. Mortality is little to none. In highly virulent strains, clinical signs can include: circling, rolling, hyperexcitability, tremors, convulsions, weakness, or flaccid paralysis of hind limbs. Mortality can be high (62% in one published outbreak).

Diagnosis is via serology or virus isolation from infected neural tissues or intestinal contents. Transmission is fecal oral. Viral diseases do not respond to antibiotics (including Baytril) and there is no treatment for TMEV. Viremia (viral presence in the blood) tends to be transient. Less virulent strains of disease can cause biphasic disease. This consists initially of acute poliomyelitis (inflammation of the grey matter of the nervous system) followed later by late-onset demyelinating [loss of the myelin around neurons (nerve cells) with dysfunction of movement (e.g. difficulty walking)]. Virus can persist in the neural tissues for over a year. Information on persistence of virus in the environment was not indicated in either reference.

Summary and Conclusions:

Animals with viral meningitis would not respond to antibiotic therapy. In my opinion where clinical signs respond to antibiotic therapy, the cause usually bacterial. Mycoplasma infections are extremely common and infection with virulent strains of TMEV are uncommon. The only way to try and determine what an animal has is to do diagnostic testing. Culture can be performed on clinically affected animals and histology/serology on terminally ill animals.

Most veterinary schools do not teach diseases of rats and mice. In schools that do offer courses in the disease of rodents and other pocket pets, attendance is often small. There are several books that cover the disease of rodents. The following two are my favorite. Information on rodent diseases can also be found in the “Journal of Comparative Medicine.”


Dean H. Percy & Stephen W. Barthold Pathology of Laboratory Rodents & Rabbits 2001. Iowa State University Press.

National Research Council Infectious Diseases of Mice and Rats 1991.

Carmen’s Answer to questions from Ronny
A What antibiotic to use is the 64 thousand dollar question. In general, for routine infections when you place an animal on antibiotics for a bacterial infection, the time course is frequently 14 days. However, it can vary depending up the location of the infection, type of antibiotic, and disease. In the case of lung infection with Mycoplasma pneumonia, the duration of treatment can be indefinite. The use of antibiotics for only 2–3 days at a time can lead to bacterial resistance to the antibiotic. Some antibiotics kill the bacteria outright, some just stop them from multiplying and allow the animal’s immune system time to kill them. Penicillin based antibiotics such as Amoxicillin, typically require a minimum of twice a day dosing for 14 days. Baytril can be once a day to twice a day. Tribrission can be used once a day to twice a day as well. The amount of antibiotic to use per kg of body weight depends on a number of factors including: the location of the infection, the age of the animal, the severity of the infection, etc. Baytril can cause problems in growing animals and is not recommended for use in pregnant, nursing, or growing animals.

Karen Robbins’ Answer to Andria
A Any time you have ill animals and your vet is unable to diagnose the problem, you should always send the infected animal in for a complete necropsy, serology, bacteria testing, and pathology. Your vet would need to take some of the samples and prepare the body to be sent in. There are several places that your vet can send animals to that will do the necessary testing. Here are a couple of places: IDEXX BioAnalytics and Charles River.

You might consider sending in one or two of your mice if they get any worse so you know what you are dealing with.

Recently, I had a rat with several problems that three different vets were unable to figure out what the exact cause was. She was treated for many different problems but nothing helped. When she became very old and started to really have problems, I had her euthanized and sent in for all the above testings I mentioned. Turns out the pathologist found she had leukemia and all of her problems were a result of that. *

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Updated February 2, 2019