Pathology and parasite distribution in mice challenged with <i>Toxoplasma gondii</i> from different geographical origins

<i>Toxoplasma gondii</i> (<i>T. gondii</i>), a zoonotic parasite, can cause severe disease in warm-blooded animals. Pathological changes in murine tissues infected with different <i>T. gondii</i> isolates were studied to establish factors influencing lesion severity and parasite burden. In Study A, mice were orally inoculated with genotype #3, #6 or #8 oocysts. In Study B, mice were inoculated intraperitoneally with genotype #1, #3, #6, #13, #141 or #265 tachyzoites. Mice were euthanised serially and tissues processed for histopathology. In Study A, genotype #6 caused pathology in the liver, brain, lung, intestine and kidney, predominantly associated with tachyzoites, while #8 caused mainly moderate pathology in the brain, lung and liver, usually associated with tissue pseudocysts/cysts. Genotype #3 occasionally caused mild pathology, but the parasite was not visible in examined tissues. In Study B, genotypes #13 and #6 caused systemic infections associated with tachyzoites. Genotypes #3, #141 and #265 caused moderate pathology associated with pseudocysts/cysts in the brain and tachyzoites in peripheral organs. Genotype #1 caused mild pathology associated with pseudocysts/cysts in organs assessed. Comparison of genotype #6 between studies showed parasite stage and inoculation method did not affect the severity of pathology, but for #3, pathology was more severe when mice were inoculated intraperitoneally with tachyzoites compared to those inoculated orally with oocysts. This study confirmed route of infection, <i>T. gondii</i> strain, life stage and dose influence infection outcome and ultimately contributes to the refinement of <i>T. gondii</i> pathogenesis knowledge, which is fundamental for toxoplasmosis management and treatment.