Reduced cognitive function in children with toxocariasis in a nationally representative sample of the United States
Graphical abstract
Highlights
► Associations between infection with Toxocara spp. and cognitive function in children aged 6–16 years are reported. ► Infected children showed poorer cognitive function, even after adjustment for sociodemographics and blood lead levels.
Introduction
Despite adequate health resources, the United States continues to experience significant within-population disparity in health and morbidity (Adler and Rehkopf, 2008). Such disparities are often defined by the socioeconomics of ethnicity and poverty. Moreover, while the contributors to health disparity are multifaceted, neglected communities consistently manifest poorer health due to both chronic and infectious disease. Indeed, the distinctions between chronic and infectious disease may be difficult to distinguish, particularly with respect to the occurrence of what have been referred to as the neglected infections of poverty (Hotez, 2008). Neglected infections of poverty (NIP) are typically chronic infections, which often lead to chronic disease such as asthma, cardiovascular disease and poor cognitive development (Hotez, 2008, Hotez and Wilkins, 2009).
One such NIP in the United States is toxocariasis. It has been suggested that toxocariasis may represent the most important NIP in the United States (Hotez and Wilkins, 2009). Studies based on NHANES III have reported relatively high seroprevalence of Toxocara spp. antibodies (Won et al., 2008, Congdon and Lloyd, 2011). While the overall seroprevalence of Toxocara infection among all age groups was estimated at close to 14%, there were also marked differences across ethnic groups, with a seroprevalence of 21.2% among African-Americans, 10.7% among Mexican-Americans and 12.0% among Whites (Won et al., 2008). Most Toxocara infections are thought to be asymptomatic and acute complications, such as visceral or ocular larva migrans, rare. While acute complicated toxocariasis is indeed rare, this may not be the only relevant clinical presentation. Rather, more insidious chronic disease involving the lungs, vasculature and CNS may be more prevalent than previously expected and, thus, of greater public health significance (Hotez and Wilkins, 2009). With respect to neurological involvement, previous investigations have identified an inverse association between toxocariasis and cognitive function in children, wherein those infected with Toxocara spp. demonstrated poorer performance on multiple cognitive assessment instruments (Marmor et al., 1987, Nelson et al., 1996). Nevertheless, these studies were limited by small sample sizes (Marmor et al., 1987, Nelson et al., 1996) and incomplete control of confounding (Nelson et al., 1996).
To explore the possible relevance of toxocariasis as a neglected infection we sought to identify its association with cognitive function in children. This study tested the differences in two cognitive performance examination components between children with and without serological evidence of Toxocara spp. infection in a large representative sample of children living in the United States.
Section snippets
Survey and laboratory procedures
The relationship between Toxocara infection and cognitive function among US children was tested using data from NHANES III conducted between the years of 1988 and 1994 by the National Center for Health Statistics at the Centers for Disease Control and Prevention (CDC), USA. Methods describing this national survey have been reported previously (National Center for Health Statistics, US Department of Health and Human Services (DHHS). Third National Health and Nutrition Examination Survey,
Results
The overall prevalence of previous Toxocara infection among children aged 6–16 years in the NHANES III was 13.4%. Differences in sociodemographics, risk factors and measures of cognitive function are presented in Table 1. All four measures of cognitive function in math (P < 0.001), reading (P < 0.001), the block design performance (P < 0.001), and the verbal digit span (P < 0.001), were significantly reduced in children with previous Toxocara infection. The mean math and reading scores from the WRAT-R
Discussion
To the best of our knowledge, this is the first report of an association between Toxocara infection and childhood cognitive function in a nationally representative population-based sample of children in the United States. This investigation identified an independent inverse association between Toxocara infection and each of the four measures of cognitive function, wherein those with serological evidence of Toxocara spp. infection on average scored 0.76 points lower on the math test, 0.69 points
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