American Fancy Rat & Mouse Association

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

Mouse Keeping: Mouse Maladies: Inherited and Environmentally-caused Conditions

By Virginia Pochmann

From Mouse Review, Issue No. 7 (May 1989) and Issue No. 8 (June 1989). Permission given to reprint articles.

Mice are subject to a larger number of contagious and infectious maladies, which once started, can take over a colony in epidemic fashion. Research laboratories which work with mice use elaborate prevention systems to ensure that no pathogens can reach their animals in which they have invested many years of research and many millions of dollars of grant money. Unfortunately, the mouse fancier can afford neither the time nor the money to follow such precautions as barrier tops for cages, procurement of mice which are SPF (specified pathogen-free), and exclusion from the colony of all people and animals which may have been in contact with infected mice. We take many chances with our colonies, such as taking animals to shows and reintroducing them to our own mouseries later, bringing other fanciers into our mouseries to see our animals, and worst of all, introducing new mice which may be carrying latent disease.

Reasonable attempts at disease prevention by fanciers may include some or all of the following measures:

  1. Any new animals are quarantined for a minimum of 3 weeks. This period is usually adequate to show up any viral disease which may be incubating. It is not adequate to rule out bacterial diseases which may be present in a latent, carrier state.
  2. Visitors to the mousery may be asked not to handle the animals themselves, and you may bring out one cage at a time to show your mice, rather than take a chance on the visitor tracking in a pathogen on his/her shoes or clothing from his own mousery.
  3. Water bottles may be quickly and easily disinfected each time they are refilled. Dip the empty bottle and rubber-stopper-and-tube assembly into a solution of house-hold bleach (use 8 ounces of bleach to 2 gallons water) for 60 seconds. Rinse in two changes of clear water before refilling.
  4. Cages should be washed and disinfected before changing animals in them.

Many of the diseases mice are subject to are incurable, so prevention is worthwhile.

Antibiotics may be tried when bacterial infections are present and will usually suppress the symptoms, but will not eliminate the carrier state from the colony. Veterinarians will all tell you that the only cure is culling the infected animals. If there are healthy-appearing carriers still present, you will soon know it because the disease will reappear. They recommend culling the entire colony and beginning again with clean animals, but fanciers usually have too many years of blood, sweat, and tears, not to mention selective breeding, in their colonies to be willing to do that. To be successful, one must cull every infected animal and every animal which was ever caged with that animal, and follow strict cleanliness and disinfection practices to avoid transferring bacteria from one cage to another. It can be done, in some cases, if you persist and are very careful, and if you kept good records of matings and cage mates, so that you know which animals must be culled.

The only way to know what you are dealing with on bacterial diseases is to have a culture made from a living mouse which is showing symptoms. (A culture can be made only from a living mouse, not from a dead animal which you send in for necropsy. This is because E. coli bacteria overgrow everything within 15 minutes after death, making it impossible to isolate your pathogen.) Diagnosis of a lot of bacterial diseases depends on culture of the tissue and isolation of the organism responsible. Therapy is then determined by testing the bacterium in culture to find which antibiotics it is sensitive to.

Antibiotics are useless in treating viral diseases, except where secondary bacterial infections are part of the problem. Viral diseases are spread by the fecal-oral route, as well as through nasal secretions, urine, aerosols from cage litter, and often through the placenta from mother to fetus. Animals which survive viral diseases may remain as shedders of the virus for weeks. Some of the viruses may be carried by humans, who then may infect mouse colonies.

Inherited and Environmentally-caused Conditions

Some of the other causes for pathological conditions and/or behaviors.

  1. Waltzing or spinning in circles, is caused by an inherited defect in the organ of balance in the inner ear. Deafness may accompany waltzing. Such mice should not be used as breeders.
  2. Looping (jumping repeatedly against the lid of the cage and landing on the feet again) may be repeated over and over for hours on end, and the mouse may do damage to itself in the process. This is an inherited nervous disorder.
  3. Kinked or malformed tails may be hereditary. Cull these.
  4. Maloccluded teeth may be hereditary. In this condition, the upper and lower incisors do not meet and wear normally against each other. The lower teeth may grow up and out of the mouth. Upper teeth grow in an arc back inside the mouth up and into the palate. Do not breed mice with this defect. [In all my years of breeding mice, I have never had one with the problem. Karen Robbins]
  5. Barbering (hair chewing) may be either hereditary or learned behavior. Some strains of mice seem to produce frequent hair chewers. This usually begins with one individual chewing the whiskers off every other mouse in the cage, then progresses to shaving the hair off their faces and shoulders. (The culprit is the only mouse in the cage who still has whiskers!) When this mouse is removed from the cage, another will frequently take over the role of barber. Hair will grow back in 60–90 days, but is frequently of another color. Example: Black mice may regrow grey hair.
  6. Patchy Hair Loss may be due to extreme old age or to ectoparasites. Several species of mites and lice may infest mice and may cause severe itching, overgrooming, and scratching, with subsequent hair loss and even self-mutilation, open sores, and ulcers which do not heal. Some strains are more resistant to ectoparasitism than others, and some individual mice within a strain are more resistant than others. Some individuals will keep their own parasite populations down to a level that doesn’t bother them, particularly if caged with other mice. Mutual grooming between mice helps remove the eggs and parasites from the hairs of the neck and other hard-to-reach places where the mouse cannot groom itself effectively. Some mice become allergic to ectoparasite bites and scratch themselves violently and ceaselessly, causing open sores which do not heal. [For parasites, Ivermectin is the treatment of choice now. KR]
  7. Rough Coat is a symptom of poor condition. This may be caused by illnesses, old age, cold temperatures, damp cages, or stress from fighting, as well as by ectoparasites.
  8. Abortions and Infertility may be caused by infectious disease such as Pasteurella pneumotropica, and also by the following factors:
    1. Chemicals (dichlorvos, etc.)
    2. Disrupted light cycles (Mice should have steady cycles of 12–14 hours of daylight, 10–12 hours of darkness, to breed well. Lights turned on at night in the mousery may be disruptive to breeding cycles, especially if mice are housed in clear plastic cages.)
    3. Overcrowding (Females often fail to come in heat when overcrowded. Nature’s population control.)
    4. Noises (Particularly sudden loud noises to which the mice are unaccustomed, and high-pitched sounds in the ultra-sonic range. These can produce extreme stress and even audiogenic seizures and death.)
    5. Inbreeding (When practicing inbreeding, watch out for decreasing litter size and/or reluctant breeders, and select against these traits. Not all inbreeding programs are troubled by this tendency, but some are.)
    6. Low temperatures (Below 65°F some strains of mice may cease to breed.)
    7. Malnutrition (Lack of sufficient animal proteins and/or Vitamin E in the diet can occasionally cause low fertility. If feeding a laboratory pelleted diet made especially for mice, there is very little chance of this being a problem. However, all of these milled pellets should be used within 90 days of the date of manufacture, which is marked on the bottom of the bag. After this date, there is some loss of quality. If you have a large freezer, these feeds will keep much longer in the freezer.
  9. Desertion or Destruction of Litters may be caused by:
    1. Disturbing nest or handling young within 2 days of littering.
    2. Insufficient nesting material (shredded paper or hay to make a cozy, private nest)
    3. Cold (interior of nest must be at 86 degrees F for young to thrive).
    4. Small litter (one or two babies may be abandoned by mother or eaten).
    5. Abnormal young
    6. Lack of milk (usually due to lack of calcium). I always give one tablet of Calcium lactate to the doe as soon as I see that she has kindled. Most will ignore it, but the occasional one needs it.
    7. Ectoparasites on the doe
    8. Dirty cages
    9. Disturbances in the environment (noises, presence of cat or dog, children, etc.)
    10. Hereditary factors (some strains seem to be poor mothers due to genetic predisposition.)
  10. Unexpected Sudden Deaths may be caused by certain infectious diseases such as Tyzzer’s Disease or Mousepox, or by the following factors:
    1. Heat stress (mice exhibit discomfort over 85 degrees F, and begin dying between 90 and 95 degrees)
    2. Dehydration (often due to malfunctioning water bottles)
    3. Stress from fighting (between males). The vanquished male may die if he cannot escape from the aggressor.
    4. Overdosage of antibiotics or other medications.

References and good books to have:
The Biology and Medicine of Rabbits and Rodents (third edition) by John Harkness and Joseph Wagner. 1989. Lea and Febiger Publishing Co., Philadelphia, PA. ISBN 0-8121-1176-1.

Merck Veterinary Manual (sixth edition). 1986. Published by Merck & Co., Inc., Rahway, N.J. [The Merck Veterinary Manual is now selling their 50th Anniversary Edition and articles on rodents are available online on the Merck site KR]

The Mouse In Biomedical Research, Volume 2 (Diseases). Editors: Foster, Small, and Fox. 1982. Published by Academic Press. (This is a large hardcover book, written for laboratory scientists, in lab terminology, and is very expensive.) [This book is now on its 2nd Edition, published in 2007, ISBN 0123694566 and is available to purchase online. Volume 1 is on “History, Wild Mice, and Genetics,” Volume 3 is on “Normative Biology, Husbandry, and Models,” and Volume 4 is on “Immunology.” KR] *

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Updated March 19, 2014