Lytic and turbid plaque-type mutants of lymphocytic choriomeningitis virus as a cause of neurological disease or persistent infection.

Mouse-passaged lymphocytic choriomeningitis (LCM) virus was found to contain a mixture of two different plaque-type mutants when plated on BHK-21/13S cells in agarose suspension. One mutant gave rise to clear plaques, with death of the cells, whereas the other produced turbid plaques which were sometimes very difficult to see. The clear-plaque variant caused a pronounced cytopathic effect on BHK-21 cells, but the turbid variant caused none; it also interfered with the cytopathic effect due to the clear variant. Brain-passed LCM virus was found to consist mainly of the clear-plaque-type, whereas liver-passed virus was mainly turbid-plaque-type. The clear type induced convulsions and early death after intracerebral inoculation of adult mice; the turbid variant caused no convulsions and late deaths. In newborn mice, the clear-plaque-type was uniformly fatal, whereas the turbid variant caused no deaths but instead induced persistent tolerant infection.