Exploring the relationship between Toxoplasma gondii seropositivity and anxiety disorders in companion dogs (Canis lupus familiaris)

Toxoplasma gondii is a widespread apicomplexan protozoan parasite that can infect a variety of warm-blooded species, exploiting numerous transmission pathways, including the ingestion of oocysts or tissue cysts. Recent research has revealed that neural localization of bradyzoite cysts in intermediate hosts potentially can lead to behavioural modifications. This double-blinded study explores the correlation between serological evidence of exposure to T. gondii and anxiety disorders in companion dogs. Furthermore, we evaluated risk factors for exposure to T. gondii, such as the consumption of raw meat, the lifestyle, and cohabitation with cats. A veterinary surgeon specializing in animal behavior classified 124 dogs as either affected or unaffected by anxiety disorders through a comprehensive behavioral visit. This expert also collected detailed anamnestic information on all the subjects. Additionally, T. gondii indirect fluorescent antibody test (IFAT) for IgG was performed on serum samples of each subject. Through a ROC curve analysis, the population was divided based on dog size, with small-breed dogs (weighing less than 15 kg) and large/medium-breed dogs (weighing over 15 kg). The study found that smaller dogs exhibited a 2.4 times higher risk (p = 0.02) of developing anxiety disorders compared to large/ medium-breed dogs, regardless of T. gondii exposure. Conversely, larger dogs were more likely (3.41 times; p = 0.07) to develop anxiety disorders when testing positive for T. gondii. Furthermore, the results indicated that dogs regularly consuming raw meat were more likely to test positive for T. gondii antibodies, with a significant (p = 0.03) risk of 2.94. These findings suggest a potential link between T. gondii exposure and the development of anxiety disorders in dogs, with the consumption of raw meat acting as a contributing risk factor. However, it is essential to recognize that the onset of anxiety disorders is influenced by multiple factors.