Association between toxocariasis and cognitive function in young to middle-aged adults.

The ascarid nematodes Toxocara canis (Werner, 1782) and Toxocara cati (Schrank, 1788) may infect humans resulting in toxocariasis. A prior study associated species of Toxocara Stiles, 1905 with cognitive deficits in children. To determine if a similar association between toxocariasis and cognition exists in adults, we analysed a large dataset from the United States' Center for Disease Control's National Health and Nutrition Examination Survey. We used linear-regression and multivariate models to examine the association between toxocariasis as assessed by the presence of anti-Toxocara IgG antibodies and three measures of cognitive function - simple reaction time (SRT), symbol-digit substitution (SDS) and serial-digit learning (SDL) in 4 279 adults aged 21 to 59 years. Toxocara seroprevalence did not vary with age or blood-lead concentration but did vary with gender, ethnicity, educational attainment and poverty-to-income ratio. Controlling for gender, age, blood-lead concentration, educational attainment, ethnic background and the poverty-to-income ratio, we found that toxocariasis predicted worse performance on the SDS but not on the SRT or the SDL. Moreover, there were significant interactions between toxocariasis and age, gender and educational attainment. In conclusion, toxocariasis appears to be associated with decreased cognitive function. Interactions between toxocariasis and gender, age and educational attainment further suggest that certain groups may be more susceptible than others to the cognitive dysfunction associated with toxocariasis in adults.