Mice and Rats
Medical Conditions

Chronic Murine Pneumonia (Murine Mycoplasmosis)
Mycoplasma pulmonis is a very elusive bacteria that causes one of the most common and serious infections of rats and mice.
The organism is difficult to isolate by standard laboratory culture procedures. As a result, a presumptive diagnosis is typically made based on the patient’s signs and symptoms.

Signs of mycoplasmosis include sniffling, sneezing, labored breathing, squinting, red-brown tearing and a rough hair coat. If the inner ear becomes infected, a head tilt and neurologic signs develop. In addition to respiratory signs, a genital infection may occur. Manifestations of the genital form include infertility, embryonic resorption and small litter size. Compromise to the respiratory tract by other bacterial or viral infections or exposure to inhalant irritants can increase the severity of mycoplasmosis. The disease runs a chronic course, which may result in death if not treated early.

Antibiotic therapy should be initiated at the first suspicion of infection. Due to the chronicity, long-term treatment by antibiotics in the drinking water may be necessary to suppress the infection. Severely affected individuals may need injectable medications and extensive supportive care. In addition, secondary infections with other organisms are common, sometimes requiring the use of multiple medications. The goal of therapy is to reduce the severity of symptoms, but complete elimination of the infective bacteria is practically impossible.

The disease is highly contagious. The bacteria is spread by direct contact with affected individuals or from an affected mother to her unborn young while still in the womb. Transmission usually occurs through respiratory aerosol and sexual activity. Rabbits, guinea pigs and other rodents can serve as carriers of the disease without exhibiting clinical signs. Other mice and rats can also serve as carriers. It is extremely important to restrict contact between mice and rats of unknown health status until a quarantine period has elapsed. A quarantine period of four to six weeks is recommended. Any animal exhibiting even the slightest signs of respiratory illness should remain isolated.

Tyzzer’s Disease
A common infectious disease of rodents is Tyzzer’s disease, caused by a bacteria (Bacillus piliformis) that infects living cells. The disease causes a high death rate in young, stressed rodents, particularly mice and gerbils. Clinical signs are nonspecific, but primarily appear as ruffled fur, lethargy, hunched posture and poor appetite. Diarrhea may also be present. The disease causes changes in the heart, liver lymph nodes and digestive tract, which can be observed at necropsy.

Prevention is the key to this disease. Strict sanitation and minimal stress greatly reduces the occurrence of this disease in colony situations. This disease can be carried by apparently normal looking rodents, which can cause disease in others. Tyzzer’s disease usually affects rodents that are stressed by weaning, shipping and adjusting to new environments. Thorough sanitation prior to introduction of new animals is important in preventing outbreaks.
© 2004 Midwest Bird and Exotic Animal Hospital