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Abstract
We critically review and summarize information on the prevalence of Toxoplasma gondii
infections in rats, mainly Rattus norvegicus, and their possible role as a source
of infection for larger carnivores and omnivores. We also review information on immunology
and natural resistance, contributing to the model value of rats in the analysis of
human infection. Rats can be successfully infected with oocysts (sporozoites), tissue
cysts (bradyzoites), and tachyzoites. Even adult rats, that are resistant to clinical
toxoplasmosis, can be infected orally with a few oocysts or tissue cysts. Infections
with tachyzoites of the RH strain are highly variable. Congenital transmission of
T. gondii occurs at a high rate when rats are infected during pregnancy. Congenitally
infected rats can harbor viable T. gondii in the absence of detectable antibodies
to T. gondii and rats with low antibody titers may harbor few or no organisms. The
isolation of viable T. gondii by bioassay is the only reliable means to determine
persistence of chronic T. gondii infection in feral rats. No evidence was found for
maintenance of T. gondii in rats by vertical transmission in the absence of cats.