Heterogeneous neuroanatomical distribution of Toxoplasma gondii parasitic elements and associated lesions in the brain of naturally infected red foxes ( Vulpes vulpes ) from Italy and Australia

Parasite-induced behavioural modification is described for many taxa, with parasites able to affect the survival, reproduction and predator-prey dynamics of the hosts. A notable example is Toxoplasma gondii, a zoonotic intracellular protozoan with a global distribution and a marked tropism for the brain, where it forms tissue cysts. Latent toxoplasmosis has been associated with behavioural alterations across multiple host species, including reduced predator avoidance and increased risk-taking behaviours. The anatomical distribution of the parasite within the brain is poorly studied in naturally infected wild carnivores. The aim of this study was to investigate if T. gondii elements or associated lesions are present in brain regions involved in behavioural processes, and whether their distribution suggests a region-specific tropism or a stochastic colonization pattern. Red fox brains from Italy (n = 25) and Australia (n = 75) were examined for the presence of T. gondii and associated lesions. Serological analyses revealed parasite prevalences of 52% in Italy and 37.3% in Australia. Histopathological examination identified focal to multifocal necrotizing and non-suppurative inflammatory lesions in seven seropositive animals. T. gondii was histologically detected in two foxes and confirmed by PCR and immunohistochemistry. Lesions were heterogeneously distributed mirroring findings observed in murine models, suggesting a stochastic pattern of brain colonization rather than a region-specific tropism. Brain areas involved were the prefrontal and frontal cortex, basal ganglia, thalamus, amygdala, hippocampus and midbrain; all brain regions associated with behavioural regulation. Presence of lesions in those areas may provide a neuropathological basis for previously reported behavioural abnormalities.