Abstract
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.
Highlights
Accumulating evidence suggests that infectious diseases can be associated with impaired cognitive function (Aiello et al 2006, Katan et al 2013) including dementia (Malaguarnera et al 2004, Kountouras et al 2006, Kusbeci et al 2011, Lurain et al 2013)
Caused by the ascarid nematodes Toxocara canis (Werner, 1782) and Toxocara cati (Schrank, 1788), toxocariasis can be transmitted to humans via eggs in dog and cat faeces after embryonation in soil or on vegetables, there is evidence that exposure to infected, undercooked meat may result in infection (Sturchler et al 1990, Despommier 2003, Fillaux and Magnaval 2013)
While there were no significant differences in seroprevalence between age groups (p = 0.068), seroprevalence varied among race-ethnic groups (p = 0.029), with non-Hispanic blacks having a seroprevalence of 21.0%, compared to 12.8% for Hispanics
Summary
Accumulating evidence suggests that infectious diseases can be associated with impaired cognitive function (Aiello et al 2006, Katan et al 2013) including dementia (Malaguarnera et al 2004, Kountouras et al 2006, Kusbeci et al 2011, Lurain et al 2013). Larger, and better controlled study that included data from a national survey in the United States conducted by the Centers for Disease Control, Walsh and Haseeb (2012) found that children seropositive for Toxocara antibodies performed more poorly on standard tasks measuring attention and perceptual reasoning and on two measures of academic achievement compared to se-.
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