Transient nature of Toxoplasma gondii-induced behavioral changes in mice

Many parasites induce specific changes in host behavior that promote the tr ansmission of their infective stages between hosts. Toxoplasmosis in rodent s is known to be accompanied by specific behavioral changes (shift in activ ity level, learning capacity, acid novelty discrimination) that can theoret ically increase the chance of infected animals being eaten by the definitiv e host, the cat. However, toxoplasmosis is also accompanied by many patholo gical symptoms. It is not known whether the behavioral changes are products of manipulation activity of the parasite or only nonspecific by-products o f pathological symptoms of toxoplasmosis. Here, we compared the dynamics of development of behavioral and pathological changes in Toxoplasma gondii-in fected mice. The results showed that the maximum reduction of mouse activit y corresponded with the peak of pathological symptoms, and also that maximu m increase of reaction times corresponded with the peak of development of t issue cysts in the brains of infected mice. Behavioral changes were only tr ansient and disappeared before the 12th wk postinoculation. The results sug gest that the behavioral changes in infected mice reported by many authors and observed in our experiments could be nonspecific by-products of patholo gical symptoms of toxoplasmosis rather than specific products of manipulati on activity by the parasite.