Low-virulence Strains of Toxoplasma gondii Result in Permanent Loss of Innate Fear of Cats in Mice, Even after Parasite Clearance

Low-virulence Strains of Toxoplasma gondii Result in Permanent Loss of Innate Fear of Cats in Mice, Even after Parasite Clearance
Wendy Marie Ingram, Leeanne M Goodrich, Ellen A Robey, Michael B Eisen
(Submitted on 1 Apr 2013)

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 pathogenmediated behavioral change remain unknown. To begin exploring these questions, we evaluated the effects of infection with isolates from the three major North American clonal lineages of T. gondii. 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 all three major clonal lineages of parasite. Surprisingly, we found that infection with an attenuated Type I parasite results in sustained loss of fear at times post infection when neither parasite nor ongoing brain inflammation were detectable. This suggests that T. gondii-mediated interruption of mouse innate aversion of cats may occur during early acute infection in a permanent manner, not requiring persistence of parasite cysts or continuing brain inflammation.

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