Serological and molecular detection of Toxoplasma gondii in cats in Europe with evaluation of associated risk factors for pathogen contact/infection.

Objectives: Toxoplasma gondii is an obligate intracellular coccidian pathogen, with domestic cats and other members of the Felidae family serving as its definitive hosts. The aim of the study was to identify risk factors for positive test results.

Methods: A laboratory database was screened for T gondii PCR results from faecal samples and serology results (IgM, IgG) from serum/plasma taken from cats in Europe between January 2008 and December 2022. Logistic regression analysis was performed to identify risk factors associated with positive T gondii results, such as breed, age, sex, neuter status, regionality, seasonality, feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV) status. Odds ratios (ORs) were calculated.

Results: A total of 45,523 cats were included: 14,500 (31.9%) tested positive by direct and/or indirect detection methods for T gondii (PCR: 126/7896 [1.6%], IgG: 14,148/37,882 [37.3%], IgM: 1539/37,882 [4.1%]). Age >5 years (IgG: OR 2.591, P <0.001; IgM: OR 1.954, P <0.001), European domestic shorthair cats/cross breeds (IgG: OR 3.848, P <0.001; IgM: OR 2.152, P <0.001), male sex (IgG: OR 1.134, P <0.001), neuter status in male (IgG: OR 0.536, P <0.001) and female cats (IgG: OR 0.577, P <0.001), FeLV antigen positivity (IgG: OR 1.358, P = 0.030) and FIV antibody positivity (IgG: OR 2.350, P <0.001; IgM: OR 2.650, P <0.001) significantly impacted the serological results. In PCR testing, neuter status had a significant impact in male (OR 2.455, P = 0.002) and female cats (OR 2.988, P <0.001). Serological and PCR results were significantly influenced by regionality for IgG (central: OR 1.454, P <0.001; north: OR 0.768, P <0.001; south: OR 0.526, P <0.001; east: OR 0.768, P <0.001; west: OR 0.709, P <0.001), IgM (central: OR 0.616, P <0.001; north: OR 1.456, P <0.001; south: OR 1.767, P <0.001; east: OR 1.456, P <0.001) and PCR testing (central: OR 0.460, P <0.001; north: OR 3.020, P = 0.002; east: OR 3.020, P = 0.002). Seasonality had a statistically significant impact on IgM (summer: OR 1.402, P <0.001; winter: OR 0.732, P <0.001) and PCR testing (autumn: OR 1.473, P = 0.038).

Conclusions and relevance: Breed, age, sex, neuter status, seasonality and regionality significantly impacted serological results. Neuter status, seasonality and regionality significantly impacted the PCR results. Immunosuppression (FeLV/FIV) had a significant impact on serological results. PCR-positive cats shed oocysts and spread infection to other susceptible hosts, including humans. Surveillance is therefore recommended, taking into consideration the associated risk factors.