Chronic form of experimental rabies in mice.

The L-28 strain of street rabies virus isolated from the salivary gland of a red fox caused chronic infection in mice. After intracerebral (i.e.) infection with virus-containing fox salivary gland suspension, 13.9% of mice showed clinical signs of disease for 11--52 days. Clear-cut stages of irritation and paralysis were distinguished in the course of infection of mice. The diagnosis of chronic rabies in mice was confirmed by immunofluorescence and isolation of virus by i.c. inoculation of mice. Electron microscopic examination of the Ammon's horn of mice revealed a slow development of morphological changes connected with the formation of virus-specific structures. The gradual increase in the number and size of aggregates of viral ribonucleoprotein was followed by the appearance of membranous and tubular structures. Along with the latter, typical bullet-shaped particles of rabies virus were found in some neurons on the 43rd day of infection.