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Illnesses and Health Problems


Common Ailments: If a mouse seems ill, separate it from its cage mates (if they still appear healthy) until you can figure out what's wrong - it may be contagious, or the other mice may pick on it for being ill. It may be that the others then develop symptoms and still have to be treated, but you may also prevent futher spread of the illness.

Mites: Mites - nearly microscopic, spider-like organisms - live on the skin surface and feed primarily on skin debris. They are transmitted by direct contact between infested and unaffected rodents. Signs of infestation range from mild scratching to severe scratching with hair loss and ulceration of the skin. In lighter coloured mice you can sometimes see reddy-brown specks moving around in the fur. Mite spray made for birds can sometimes be used on mice, or ear drops for mites made for cats. Some pet shops also sell sprays made for small animals such as rabbits, rats and hamsters that is suitable for treating a general case of mites. However, this spray may only need to be used every three days: always be sure to check the instructions. Make sure that any product you buy is for mites only and not lice. Gently spray the mouse/mice with the treatment and clean the cage thoroughly. Remember to throw away anything that may provide a breeding ground for the mites, such as cardboard tubes and wooden items. It may be necessary to get a vet to prescribe Ivermectin to get rid of the infestation.

Lice: Lice may also live in the coats of pet mice and rats. They are flattened, wingless insects that suck tissue fluids and blood from the skin of the host. Lice are larger than mites and can usually be seen without a magnifying glass. Lice are most often transmitted by direct contact with infested bedding and between infested and unaffected individuals.

The lice of mice and rats are found most often on the neck and body. They suck blood and can therefore cause anaemia (and sometimes death) and transmit blood-borne diseases to rodents. Louse infestations may also cause scratching, hair loss and skin wounds. A veterinarian should be consulted if louse infestation is suspected.

Sneezing:Can be caused by sensitivity to bedding materials. Remember; NEVER use pine or cedar bedding because it can cause major respiratory problems in both mice and rats. You can try changing the bedding type and see if that stops the sneezing. Hemp, shredded paper or aspen is the most appropriate. If the sneezing continues consult a vet. It is worth remembering that you can give your mice the common cold that can quickly become serious in such a small animal and need antibiotic treatment.

Tumours: Mice are very susceptible to formation of tumours and frequently develop tumours representing a wide variety of tissue types. The tumours may be external or internal. Leukaemia (cancer involving the white blood cells) is also quite common in mice.

Owners of pet mice should seek veterinary attention at once after discovering a lump, bump or unusual mass protruding from a body opening (which could also be a polyp or prolapse). Tumours tend to grow continuously larger and may ulcerate and become infected if they reach a very large size. For this reason it is always preferable to remove them when they are small.

20-month-old mouse with a large, serious mammary tumour

Cuts: Treat with styptic powder if the bleeding will not stop naturally as blood loss is serious in mice. Use your own discretion, but some cuts should be checked by a vet. They can get infected very easily. What seems like a small infection to us can be deadly to a mouse. Keeping them alone in a clean cage is probably the best way to help a cut. Keep a very close eye on the area around the cut. If an abscess develops (with a blister-type look) contact a vet immediately as it will need to be drained by a professional.


Obesity: Overindulgent pet owners and diets rich in seeds and nuts can be responsible for this condition, but some mice also have a genetic tendancy to become obese (for example the dominant yellow colours red and fawn). Commercial diets specifically designed for mice can contain too many fatty ingredients and so should be carefully chosen or preferably mixed by the owner.

Overgrown Incisors: The incisor (or front gnawing) teeth of all rodents grow continuously during the individual’s life. The continual wear between the uppers and lowers usually prevents overgrowth of the teeth. Hereditary abnormalities of the jawbones and/or teeth, abscessation of the incisor teeth, or injury to the jaw may result in malocclusion (improper meeting of the upper and lower incisors). Malocclusion, in turn, results in overgrowth of one or more of the incisors, with subsequent injury to the mouth. Mice with this problem must have their overgrown incisors trimmed periodically by a vet.

Chronic Murine Pneumonia (Murine Mycoplasmosis): Chronic murine pneumonia (CMP), or murine mycoplasmosis is the most significant and serious bacterial infection of mice. It is caused by the rather unusual bacterium Mycoplasma pulmonis. This organism is relatively difficult to isolate because it cannot be grown in the laboratory using ordinary culture methods. This makes diagnosis of CMP difficult except for the fact that the disease is so very common and well recognised.

Signs of CMP include sniffling, sneezing, squinting, red-brown tears, rough coat and laboured and audible respiration. If the inner ear becomes involved a severe, often incapacitating head tilt usually develops. In colony situations this disease can seriously affect the reproductive capacity of female rodents, resulting in infertility and reduced litter sizes.

Because this disease tends to have a very chronic (long-lasting) course, afflicted individuals should receive antibiotic treatment as soon as the first signs are recognised. Antibiotics can be added to the drinking water for long periods. Individuals exhibiting serious, life-threatening signs must be treated aggressively with injectable antibiotics if there is any hope of helping them. Frequently other harmful bacteria complicate CMP. This often necessitates the use of multiple antibiotics.

Elimination of the Mycoplasma pulmonis organism from infected individuals is regarded by most experts as a practical impossibility. However, early treatment reduces the severity of the disease in affected rodents. The outcome of treatment is always unpredictable because there are so many factors that can have an influence on it: individual susceptibility and resistance to the causative agent; age, physical condition and nutritional status of the individual; and the presence of complicating factors (other bacterial and/or viral infections, high levels of ammonia within the enclosure, etc).

The bacterium responsible for CMP, Mycoplasma pulmonis, is highly contagious. It may be transmitted between mother and offspring in the womb during embryonic life and by direct contact after birth. Transmission among infected and uninfected older rodents results from exchange of respiratory aerosols and sexual activity.

Mice may also carry the Mycoplasma pulmonis organism without showing obvious signs of illness. This is especially true of newly acquired mice. This fact underlines the importance of restricting contact between mice of unknown health status and those whose health status has been proven by remaining disease-free for relatively long periods. Furthermore, all newly acquired mice should be quarantined (strictly confined from other pet rodents) for two to three weeks before contact with them is permitted. Any mouse exhibiting respiratory signs (no matter how mild) should never be housed with or near a healthy mouse.

The severity of CMP can be increased substantially by any agent that harms the respiratory linings. Other bacterial and/or viral infections and exposure to the irritating chemical effects of ammonia from urine within poorly maintained enclosures can complicate CMP, making the disease far more deadly.

Tyzzer's Disease: This disease is caused by the bacteriumClostridium piliforme, which is usually transmitted by consuming contaminated food or water. The bacterium may survive in spore form for extremely long periods in soil, bedding and feed and is therefore highly resistant. Signs of infection are often not apparent but may include lethargy, rough coat and sudden death. Another form of the disease results in chronic wasting and death. Diarrhoea may or may not be noted.

The disease is difficult to diagnose in individuals before death. Specific antibiotics must be used early in the course of the disease. Some evidence indicates that this disease can be transmitted to pregnant women. Therefore all necessary precautions should be taken to prevent this possibility.

Miscellaneous Bacterial Infections: Wounds (from fighting and other forms of trauma) are commonly infected with bacteria that already exist within the living quarters. Abscesses commonly result from wounds when they have gone unnoticed and untreated. Successful treatment of certain wounds (especially long and deep cuts) and abscesses requires veterinary intervention. Abscesses usually must be surgically opened because the relatively solid nature of rodent pus precludes lancing and draining them.

Sendai Virus Infection: In many mouse colonies, Sendai virus infection is the most significant and should never be housed with or near a healthy mouse. Nursing mice and those being weaned are the most commonly and seriously infected. Adult mice may become infected but rarely show signs. Signs of the infection include laboured breathing, rough coat, weight loss and death. Bacterial infections complicate the picture and usually increase the death rate. There is no specific treatment for this disease. A commercial vaccine is available but it is only of practical use with large colonies of susceptible mice.

Mousepox (Ectromelia): Mousepox is a highly contagious viral disease of mice that was only recently recognised in the United States. The mouse is the only natural host of the virus. The acute (sudden onset) form of the disease affects the entire body. Clinical signs include lethargy, hunched posture, rough coat, diarrhoea, inflammation of the eye membranes, swelling of the face and legs and death. Another form of the disease results in a body-wide skin rash. Soon the skin becomes swollen and ulcerated. Because of the resulting pain and discomfort afflicted mice begin to chew on themselves. This behaviour often becomes obsessive, resulting in amputation of appendages. There is no specific treatment for this viral disease. This virus is very unlikely to infect mice unless they were acquired from a colony with this infection already established within its members.

Intestinal Parasite Problems: Tapeworms and pinworms are the most common intestinal parasites of mice. They often go undetected unless present in large numbers. Signs of infection may include weight loss, inactivity, lack of appetite, constipation, and excessive licking and chewing of the rectal area and base of the tail. Pinworms are especially difficult (sometimes impossible) to eliminate from mice. Transmission of these parasites to people is possible but unlikely. Therefore great care should be when handling and disposing of rodent faeces.

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