Toxocara seroprevalence in the USA and its impact for individuals and society.

Toxocara species are intestinal helminths of dogs and cats, the larval stages of which may infect humans and cause severe neural, ocular and visceral larva migrans disease. Such cases of severe overt disease represent only a small fraction of the of the US population who have been exposed and infected with Toxocara, subsequently developing IgG antibodies to the larvae. The true impact of exposure to Toxocara in this large group of Americans remains uncertain. Toxocara antibody positivity is associated with poverty, but other specific risk factors have been identified, including sex, age, rural residence, region of residence, race and exposure to pets. This seropositive status has also been associated with several childhood diseases, including asthma and epilepsy, increased serum lead levels, and poor neurocognitive function. Three large-scale NHANES studies have provided comprehensive datasets, while several smaller studies have explored specific disease associations. Each seroprevalence study must be interpreted in consideration of the sensitivity and specificity of the individual serological methods employed. This chapter summarizes all historical Toxocara prevalence data from dogs, cats and soil in the United States. It then carefully examines all previous human Toxocara seroprevalence surveys performed in the United States. Data from these surveys is assimilated, compared and discussed to determine the validity of findings and to accurately identify risk factors for Toxocara seropositivity. The validity of associations of exposure to Toxocara larvae and childhood diseases such as asthma and epilepsy and effects neurocognitive function within the American context are also explored.