434 BIOLOGY OF THE LABORATORY MOUSE 



A somewhat similar organism, termed Leptospira aquicole pseudoictero- 

 genica, has been reported in the kidneys and urine of stock mice (23). The 

 strain apparently is identical with one found in water. 



Virus Diseases op Mice 



Filterable viruses have been known to produce a variety of diseases in 

 plants and animals since 1892. Only in the past 10 years, however, have 

 spontaneous diseases due to the viruses been recognized in mice. Some of 

 these diseases may spread within a mouse colony, producing highly fatal 

 results. Others may produce no visible signs of infection but are equally 

 important, since they may evidence themselves in the course of experimental 

 procedures. 



The virus diseases to be discussed are infectious ectromelia, lymphocytic 

 choriomeningitis, encephalomyelitis of mice (Theiler), virus pneumonia, and 

 salivary gland disease. The etiological agents are acceptable as viruses 

 since they fulfill one or more of the following criteria: transmissibility, 

 filterability, failure to grow on non-viable culture media, absence of culti- 

 vable bacteria, presence of inclusion bodies in the cells of the host, and 

 production of immunity. 



Infectious ectromelia. — In 1930 Marchal (162) described a new virus 

 disease of mice. It occurred principally in young mice and was noted most 

 frequently when the animals were separated from their mothers and placed 

 together in groups of 50. Subsequently, the spontaneous disease has been 

 found in England (169) and on the Continent (24, 242, 102), but has not yet 

 been reported from this country. It occurs in laboratory mice of differ- 

 ent stocks and has been found in wild mice caught in the laboratory. 

 McGaughey and Whitehead (169) found the disease to be so widespread in 

 England that difficulty was experienced in obtaining healthy mice. Some 

 animals apparently harbor the virus and develop the disease only when 

 subject to experimental inoculation (169, 102). 



The natural disease. — Qinically, the disease occurs in two forms. The 

 acute or abdominal type usually appears first in a stock of infected mice and 

 is evidenced by loss of normal activity and ruffled, lustreless coats without 

 other significant signs. No skin lesions are present. Death may occur 

 after an illness as short as 4 hours, and the fatality rate may reach 80 to 90 

 per cent in certain lots of mice. Recognition of this form may be difficult 

 unless careful autopsies are performed. 



The chronic or cutaneous form of the disease appears later in animals 

 surviving the acute type or in those previously uninfected. Here skin 



