8 LEAFLET 253, U. S. DEPARTMENT OF AGRICULTURE 
percent. Control of Salmonella infection is difficult. Generally it is ad- 
visable to destroy the entire lot, and clean and disinfect the cages and prem- 
ises before obtaining new stock. If the animals are too valuable to sacrifice, 
they may be divided into small isolated groups and the diseased ones de- 
stroyed. Cages should be sterilized. Sick animals that recover may act as 
carriers and infect the rest of the colony. Surviving males will usually be 
sterile as the disease causes pathological changes which prevent the descent 
of the testicles. 
Hemorrhagic septicemia.—This disease of mice and rats is caused by Pas- 
teurella muracida. Infection takes place mainly by contact with sick animals 
or carriers which discharge the organism in nasal and conjunctival secretions. 
Organisms also are air-borne or may be carried in food. The symptoms in 
acutely affected animals are depression, ruffled coat, loss of appetite, dis- 
charge from eyes and nose, and rapid respiration. Death occurs sometimes 
in afew hours. Infection may cause death even before signs of sickness are 
noted. At post mortem examination, the viscera are found to be congested 
and numerous capillary hemorrhages are present on the moist surfaces. In 
chronic cases, there may be enlargement of the lymph nodes and small, light- 
colored areas of necrosis in the liver. The mouse is highly susceptible; the 
rat is more resistant. For control, all affected animals should be removed 
from the colony and killed. The cages and premises should then be cleaned 
and disinfected. Highly resistant stocks should be selected for breeding. 
Pseudotuberculosis——A form of this disease, caused by Pasteurella pseudo- 
tuberculosis, is sometimes epizootic in rats. Infection takes place through 
the intestinal tract. Another form of pseudotuberculosis which occurs in 
mice is caused by Corynebacterium kutscheri (murium). Itis a rather infre- 
quent chronic disease manifested by tuberclelike lesions in the lungs; liver; 
lymph nodes of the cervical region, the mediastinum, and the mesentary; and 
isolated nodules in the spleen and kidneys. 
Mouse septicemia.—This is a relatively infrequent disease of mice caused 
by Erysipelothrix muriseptica. Conjunctivitis, pneumonia, edema of the ab- 
dominal tissues, enlargement of the spleen. and small pale gray areas of 
necrosis in the liver are the chief characteristics of this disease. The organ- 
ism causing this disease cannot be distinguished from E. rhusiopathiae which 
causes erysipelas in swine. 
Pyogenic infections.—Mice and rats may develop abscesses in the sub- 
cutaneous tissue of the head, neck, and other parts of the body. Streptococci, 
staphylococci, and other organisms are causative agents and usually gain 
entrance through surface wounds. Affected animals should be destroyed 
and the cages disinfected. Streptobacillus moniliformis has been found in 
the nasopharynx of apparently normal rats but is not responsible for any 
serious disease problem in these animals. It is highly fatal in mice, however, 
causing abscesses in the joints and internal organs. 
Pneumonia caused by pneumococci and Friedlander’s bacilli has proved 
highly fatalin mice. The disease is rare and usually due to unusual circum- 
stances. Brucella bronchiseptica sometimes causes pneumonia in mice and 
certain pulmonary diseases in rats. 
Virus Diseases 
Infections of the nervous system.—Encephalomyelitis, a somewhat rare dis- 
ease, is manifested by paralysis of the hind legs, but not the tail, of mice. It 
occurs chiefly in young animals. 
Meningoencephalomyelitis is also manifested by paralysis of the hind legs. 
Choriomeningitis in mice usually occurs as a latent infection without symp- 
toms, although infections resulting in noticeable illness have been reported. 
Man is also susceptible to the virus. 
Infection of the respiratory apparatus.—Mice can be experimentally infected 
with many types of pneumonia virus, but spontaneous illness caused by these 
viruses is rare, 
