400 BIOLOGY OF THE LABORATORY MOUSE 



normal rodents, but has also been identified as the etiological agent of 

 sporadic and epidemic illnesses. 



The etiological situation in respect to these diseases, however, is not 

 an uncomplicated one. From cultures of Streptohacilliis moniliformis and 

 from mouse and rat tissues, Klieneberger and her co-workers (125, 126, 

 127, 72) have isolated a pleuropneumonia-like organism, termed Li, which 

 alone is relatively avirulent, but in combination with the Streptobacillus 

 is markedly pathogenic for mice. The relationship between the two organ- 

 isms is not clearly established; symbiosis (125, 126) and bacterial variation 

 (48) have both been advanced as explanations. Other pleuro-pneumonia- 

 like organisms, distinct from Li, have been isolated from diseased mice, 

 and apparently play an etiological role. It therefore seems desirable to 

 discuss together the diseases produced by these two groups of organisms. 



Infection with Streptobacillus moniliformis. — This disease, which is 

 primarily an arthritis in the subacute and chronic cases, occurs both 

 sporadically and epidemically (152, 261, 161, 301). The origin of the 

 infection and the factors responsible for epidemic spread remain unknown. 

 Presumably carriers may exist within a stock or may gain access to it from 

 without (wild rodents) and thus serve as the source. The mortality is 

 usually high, but varies in different genetic strains of mice. In one epidemic 

 (161, 301) lasting 4 months, 414 of 650 Simpson-Marsh albino mice suc- 

 cumbed, whereas only 61 of about 300 Little dilute brown (dba) mice died. 

 Death may occur in a few days or at any time within 6 months or longer 

 after infection. 



The natural disease. — In the acute form the disease is septicemic in 

 character. Signs of the infection are nonspecific— the animal appears ill, 

 its coat is dull, a semipurulent conjunctival discharge is present, and occlu- 

 sion of the palpebral fissures may occur. No characteristic changes are 

 found post mortem either grossly or microscopically, but the organism may 

 be cultured from the blood and organs. In blood smears the organisms 

 appear as quite regular bacilli. 



A more characteristic clinical picture is presented in the subacute and 

 chronic cases. Polyarthritis, edema and cyanosis of the extremities and tail 

 suggestive of cardiac failure, conjunctivitis, and emaciation are outstanding 

 signs. Occasionally there occurs involvement of the vertebral column 

 resulting in paralysis of the hind legs, ulceration of the feet with serous 

 exudation and crusting but rarely gangrene, enlargement of the axillary and 

 inguinal lymph nodes, keratitis progressing to destruction of the eye, 

 arrested gestation, subcutaneous nodules, submaxillary abscesses, and 



