Toxoplasma gondii (T. gondii), a parasite that can be transmitted to humans by cats, has been proposed as a modifiable risk factor for schizophrenia and related disorders. However, much of the research examining this relationship has relied on cat ownership as a proxy measure for T. gondii exposure. This study examined the relationship between serum T. gondii levels and later psychotic experiences (PEs) and brain volume. We also explored the relationship between cat ownership and T. gondii serology. Using the Avon Longitudinal Study of Parents and Children (ALSPAC), we studied 3542 individuals for whom data on serum T. gondii during childhood and PEs at age 18 were available. Voxel-based morphometry assessed whether MRI measures of grey matter volume at age 20 were associated with T. gondii levels among a subset of the participants (N = 334). Serum T. gondii was not associated with PE group in adjusted models (suspected PEs risk ratio (RR) = 1.06, 95% confidence interval (CI) 0.89-1.27; definite PEs RR = 0.86, 95% CI 0.65-1.13; psychotic disorder RR = 1.00, 95% CI 0.73-1.38). Exposure to cats during gestation was associated with higher T. gondii in adolescence (β = 0.08, p = 0.033), while exposure to cats during childhood was not (β = 0.05, p = 0.310). T. gondii was not associated with grey matter volume in the neuroimaging sample (pFWEs ≥ 0.882, Zs ≤ 3.86). Future work examining the relationship between T. gondii and schizophrenia-spectrum disorders should focus on serology or cat ownership during gestation as a proxy measure of T. gondii exposure, as there was no association between childhood cat ownership and T. gondii.
Jesuthasan et al. (Wed,) studied this question.