  Toxoplasma gondii chronic infection in rodent secondary hosts has been
reported to lead to a loss of innate, hard-wired fear toward cats, its primary
host. However the generality of this response across T. gondii strains and the
underlying mechanism for this pathogen mediated behavioral change remain
unknown. To begin exploring these questions, we evaluated the effects of
infection with two previously uninvestigated isolates from the three major
North American clonal lineages of T. gondii, Type III and an attenuated strain
of Type I. Using an hour-long open field activity assay optimized for this
purpose, we measured mouse aversion toward predator and non-predator urines. We
show that loss of innate aversion of cat urine is a general trait caused by
infection with any of the three major clonal lineages of parasite.
Surprisingly, we found that infection with the attenuated Type I parasite
results in sustained loss of aversion at times post infection when neither
parasite nor ongoing brain inflammation were detectable. This suggests that T.
gondii-mediated interruption of mouse innate aversion toward cat urine may
occur during early acute infection in a permanent manner, not requiring
persistence of parasitecysts or continuing brain inflammation.
