Toxoplasma gondii infections are typically subclinical in humans but can cause significant problems in pregnant or immunocompromised individuals. Cats serve as a definitive host for T gondii, and oocysts shed in the feces of cats are infectious after a few days of sporulation. Findings from a previous study by these investigators in Germany suggested seasonality in the proportion of cats shedding T gondii, with a significantly higher proportion of T gondii-positive cats found between July and December than between January and June.
The purpose of this study was to determine whether seasonal shedding of T gondii and Hammondia hammondi (a close relative of T gondii) could be associated with climatic factors (ie, temperature, North Atlantic Oscillation indices, precipitation).
An overall prevalence of 0.14% for T gondii and 0.10% for H hammondi was found over the 55-month study period. T gondii was observed predominantly during summer to autumn, whereas H hammondi was found predominantly during autumn and winter. Of the climatic variables analyzed, precipitation as an explanatory variable had the least impact on statistical models, whereas temperature and North Atlantic Oscillation indices were sufficiently predictive. Time lags were also observed between climatic events and the period of time when high proportions of cats were shedding T gondii and H hammondi. The authors concluded that the findings may be important for planning epidemiologic studies and for estimating the risk for human infection.