This article is from the Fall 1997 AFRMA Rat & Mouse Tales news-magazine.

Robert C. Simpson, Cottage City, MD

Q I still have four rats and lots of mice. I’ve learned that it’s easy to keep mice, but hard to keep them healthy. I’ve been fighting a lice infestation on and off for the last 8 months. Short of destroying the whole lot, I’m not sure how to handle it. I started with 5 mice and soon had over 60. I noticed that some had tendencies to be sickly and realized they were infested with lice. I’ve sprayed with cat flea spray, given baths, separated mice, and changed bedding frequently. The problem seemed to go away, but then came back. I have one mouse that has lost her hair and regrown it three times.

Q The other thing I’m having problems with is respiratory disease. I know this is very common. I had a mouse that “perched” all day with her head down. She scratched all the time, but I could find no lice. Her eyes were runny and her face appeared swollen and deformed. After 8 months of no improvement I destroyed her. I notice others that make little clicking noises when they breathe. Again, I don’t know what to do short of starting over again with sterilized equipment and new, healthy mice.

Otherwise, the mice seem to live and get along with what I consider to be serious health problems. What do breeders or anyone with an extensive collection of mice do when hit with this situation? Am I being too fussy in my expectations of healthy mice? So far, I’ve only lost two mice in about 18 months.

Answer by Nichole Royer
A I am very sorry to hear of the problems you are having with your mice, and I think I can offer you some suggestions. Recently, a number of AFRMA members have begun using Ivermectin to treat rats and mice for external parasites. We have found that a 10% solution (9 parts propylene glycol, 1 part Ivermectin) works wonders. You put a large drop on the middle of each mouse’s head (in between the ears) and repeat in 2 weeks. No fuss, no muss, the parasites just disappear. Unfortunately, the only way to get Ivermectin over the counter, is to purchase it in huge quantities because it is formulated for cattle, which is very cost prohibitive. Most people find it easier (and cheaper) to take some animals to the vet, explain the problem you are having, and request Ivermectin. Most veterinarians are happy to comply.

There are several causes of respiratory problems in mice. The most common (and probably the one you are encountering) is caused by the bacteria Mycoplasma pulmonis. Unfortunately, Mycoplasma is incurable; however, most pet rats and mice probably have it. It is very contagious and passed from mother to offspring, between cage mates through the air, and contaminated bedding, etc. While all mice (and rats) probably have Mycoplasma, only some develop clinical symptoms. Usually, it is animals which are stressed for any reason including: old age, injury, overcrowded housing conditions, or certain kinds of bedding (cedar or pine shavings). The presence of external parasites may be stressful enough that they are contributing to the respiratory problem.

Some mice are more genetically predisposed to getting respiratory problems. It is for this reason that most breeders eliminate symptomatic animals from their program. This can be done by either euthanizing mice with symptoms (many breeders do this), or by separating them from the rest of the colony (different cages) and not allowing them to breed.

Although Mycoplasma is incurable, it is not untreatable. Many people have had good luck treating with Tylan (Tylosin), 1⁄8 tsp. dissolved in 8 oz water, changed every day. Continue for 2–4 weeks. (I personally continue for another 2–4 weeks if they have not improved. This length of treatment is not recommended, but I have never had a problem with it.) Tylan is another drug that is sold in feed stores for livestock. You usually have to buy a large bottle of it, and it’s not cheap, but it is well worth it to keep on hand. I use it any time I am stressing my animals, or if I even suspect a problem, and so far I have had great results. If your feed store does not carry it, Tylan Soluble Powder is available without a prescription through Revival Animal Health.

I do not recommend starting over again with new mice (they will probably all have it too). Try the Ivermectin for the external parasites, and the Tylan for the respiratory symptoms, and removing all mice showing symptoms from the breeding program. While you are treating them, do not breed or bring in any new stock. Keep in mind that if you have only lost two mice in 18 months, it means that your mice are probably fairly healthy. The life span for mice is usually only 1–2 years, and by the time they reach the 1 year mark, they can be considered to be at a high risk from Mycoplasma simply from age.

You are not being fussy in your expectations of having healthy mice. Most breeders do not have extensive problems with respiratory, but this is often because they have worked it out of their animals, and are extremely careful about what they bring back in. It is very unusual to hear of someone buying a mouse from a pet store and not having some type of medical problems with it. Many breeders refuse to bring in anything without first putting it through a 2 month quarantine in another part of the house away from their colony.

Answer by Carmen Jane Booth, D.V.M.
A I have reviewed Nichole’s response to Mr. Simpson’s question and made a few changes where I feel they are appropriate for clarity and medical accuracy. The only additional information that I can provide is, once animals are started on antibiotic therapy for Mycoplasmosis, the clinical symptoms usually recur once the antibiotic is discontinued. My recommendation would be to make the Tylan up daily and change the water daily. Many antibiotics precipitate in water and are destroyed by light.

For the Ivermectin to actually work, all animals must be treated and placed in clean cages, with uninfected bedding, etc. They all must be retreated exactly 14 days after the first dose. In many cases, the bedding is the fomite for the eggs, i.e. shavings from lumber mills where wild rodents have access to the shavings.

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