IXFECTIOUS DISEASES OF MICE 439 



infection of a laboratory worker (147) and experimental reproduction of the 

 disease in man by inoculation with the murine virus (145), together with the 

 above reports, suggest that mice constitute a natural reservoir of the disease. 



The natural disease. — In most instances in which the virus of lympho- 

 cytic choriomeningitis has been found in mice the infected animals have 

 appeared to be entirely normal and healthy and the disease has existed as a 

 latent infection. In the colony observed by Traub ( 292), hovsever, signs of 

 infection were noted. He describes the animals as follows: " . . . a num- 

 ber of 2 to 6 week. old mice were emaciated and drowsy. Their fur was 

 ruffled and they were often seen sitting in corners of the cage by themselves. 

 Their movements were slow and stiff, and their legs appeared long in propor- 

 tion to their thin bodies." Other signs of infection were conjunctivitis, 

 photophobia, and a slow rate of growth. No signs of involvement of the 

 central nervous system were noted. Approximately one-half of the mice in 

 the colony were infected, although the morbidity was less than 20 per cent, 

 and the mortality less than 2 per cent of the number of infected animals. 

 The majority recovered completely in 3 weeks. The active agent was 

 isolated from the blood and brain of apparently normal mice, of those show- 

 ing only conjunctivitis and photophobia, and of those obviously ill or found 

 dead. 



Xo gross lesions were found at autopsy of these animals. IMicroscopic 

 examination of the liver revealed slight perivascular round cell infiltration, 

 scattered hinphocytic infiltration in the interstitial tissue, and patchy 

 reticulo-endothelial hj'perplasia. Slight peribronchial and perivascular 

 infiltration with round cells and slight thickening of the alveolar walls were 

 found in the lungs of 2 of 12 mice. Only i mouse showed a slight meningeal 

 reaction consisting of lymphocytic cells. 



Transmission of the natural disease presumably occurs by contact, since 

 normal mice may be infected by placing them in a cage with diseased ani- 

 mals. Although the route of infection is not definitely known, it has been 

 demonstrated that the virus is often present in the urine and nasal secretions 

 of diseased mice (292) . The agent has also been found in embryo, new born, 

 and suckling mice (^138). 



The experimental disease. ^Laboratory and wild mice are susceptible 

 to virus introduced by almost any route of inoculation, but only by intra- 

 cerebral injection is a definite clinical picture produced. Following such 

 administration, an incubation period of 5 to 7 days elapses before the mice 

 appear ill. They then show signs of malaise- lassitude, ruftled fur, hunched 

 back, and partially closed eyes. Death may occur suddenly without other 



