The effect of congenital and adult-acquired Toxoplasma infections on the motor performance of mice.

Motor performance was assessed in three groups of mice infected with Toxoplasma. One group was infected when adult. Two groups were infected congenitally: the first was born to dams infected during gestation and the second to dams which were chronically infected prior to mating. All mice were placed individually on a rotating cylinder and the number of falls from it noted over a two-minute period. Infected mice fell significantly more often than uninfected controls. The difference was independent of emotionality (as measured by defaecation) and general body health (as measured by body weight and a subjectively assessed health rating). There was no significant difference in motor performance between the two congenitally infected groups. However, the offspring of mice infected during pregnancy fell significantly more often than mice infected when adult. There were no significant correlations between motor performance and the actual number of Toxoplasma tissue cysts in the brains (or in separate defined sectors of the brains) of infected mice. We suggest that differences between infected and uninfected mice result from pathological changes caused by proliferating toxoplasms in the brains of infected mice. An immunopathological reaction due to the presence of the tissue cysts may also be involved. Other possible factors contributing to observed deficits in motor performance of infected mice are discussed. We suggest that such interference with the motor performance of Toxoplasma infected mice may render them more susceptible to predation by the domestic cat, the definitive host of Toxoplasma.