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Mice and Rat Diseases/Infections

Chronic Murine Pneumonia (CMP) or Murine Mycoplasmosis: Is the most significant and serious bacterial infection of mice and rats. 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 more difficult except for the fact that the disease is so very common and well recognized. For this reason, CMP is usually diagnosed by signs of illness, without attempts to isolate the causative bacterium. Signs of CMP include sniffling, sneezing, squinting, red-brown tears, rough hair coat, and labored 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 recognized. 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 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.

Rabbits, guinea pigs, and other rodents may carry the causative agent but do not manifest signs of disease. Caution must, therefore, be exercised when allowing contact between murine rodents and these potential "carriers." Mice and rats, too, may carry the Mycoplasma pulmonis organism without showing obvious signs of illness. This is especially true of newly acquired mice and rats. This fact underscores the importance of restricting contact between mice and rats of unknown health status and those whose health status has been proven by remaining disease-free for relatively long periods. Furthermore, all newly acquired rats and mice should be quarantined (strictly confined from other pet rodents) for at least 4-6 weeks before contact with them is permitted. Any mouse or rat exhibiting respiratory signs (no matter how mild) should never be housed with or near a healthy pet mouse or rat. 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 most often infects gerbils and mice, though rats also are susceptible. It is caused by the bacterium, Clostridium piliforme, which is usually transmitted by eating 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 inapparent but may include lethargy, rough haircoat, and sudden death. Another form of the disease results in chronic wasting and death. Diarrhea may or may not be noted. The disease is difficult to diagnose in individuals before death. It is considerably easier to diagnose during an autopsy. Sacrificing 1-2 individuals of a large group and performing autopsies on them are recommended to successfully treat and perhaps spare he majority of the group. Specific antibiotics must be used early in the course of the disease. Some evidence indicates that his disease can be transmitted to pregnant women. Therefore, all necessary precautions should be taken to prevent this possibility.

Miscellaneous Bacterial Infections: A wide variety of other bacteria can cause illness n pet mice and rats. Your veterinarian is best equipped to diagnose and prescribe medications for these diseases. 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.

Viral Infections: Numerous viruses can infect mice and rats. Only few of the most important viral infections among them will be discussed.

Sendai Virus Infection: In many mouse colonies, Sendai virus infection is the most significant and how mild) should never be housed with or near a healthy pet mouse or rat. 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 labored breathing, rough haircoat, 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.

Sialodacryoadenitis: Sialodacryoadenitis is a highly contagious viral disease of rats and recently weaned mice. Initial signs include squinting, blinking and rubbing of the eyes. Later, sneezing and swelling in the neck region are noted. As the disease progresses, swellings below or around one or both eyes, bulging of the eyes, red-brown tears, and self-trauma to the eyes are noted. Respiratory signs also may occur. There is no specific treatment for this viral disease. This virus is very unlikely to infect pet rats and mice unless they were acquired from a colony with this infection already established within its members.

Mousepox (Ectromelia): Mousepox is a highly contagious viral disease of mice that was only recently recognized 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 haircoat, diarrhea, 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 behavior often becomes obsessive, resulting in amputation of appendages. There is no specific treatment for this viral disease. This virus is very unlikely to infect pet mice unless they were acquired from a colony with this infection already established within it members.