Virulence Alterations of Tacaribe Virus Infection in Adult Mice: Lethal Model for Fatal Encephalitis.

Selection of lethal substrains of Tacaribe virus strain 11573 was done by successive serial intracerebral I.c. passage of the virus in adult mice. Substrains have been partially characterized in suckling, weanling, and adult mice by determination of percent mortality and calculation and calculation of median intracerebral lethal dose values, and by histopathologic changes observed in brains of adult mice. Some of the derived virus substrains produced 80-90 mortality by second or third adult i.c. passage and maintained this virulence for 1 - 3 passages, after which the virulence rapidly declined with subsequent passages. Clinical signs of infection in adult mice were manifested by a rough hair-coat, ventriflexed posture, diminished activity, increased excitability, flaccid hind-limb extension with progressive paralysis and death. Histologic examination revealed meningoencephalitis. Author