Using a nationally representative set of banked sera, the CDC has undertaken two major national surveys for toxocariasis. The first was reported more than 20 years ago using sera from children aged 1 to 11 that were collected during the first Health and Nutrition Examination Survey (HANES I) of over 23,000 persons 1 to 74 years of age in 35 geographic regions from 1971 to 1973.
Nationwide, the overall prevalence was found to vary between 4.6% and 7.3%, but ranged as high as 10% in the American South and over 30% for socioeconomically disadvantaged African American children. Higher seroprevalence was also linked to markers of low socioeconomic status, including poverty and crowding and lower educational level for head of household.
In 2008, the CDC again reported on Toxocara seroprevalence from the Third National Health and Nutrition Examination Survey (NHANES III), a cross-sectional survey conducted between 1988 and 1994. The survey sampled at higher rates specific minority groups (e.g., non-Hispanic blacks and Mexican Americans) and age groups (young children and the elderly). Based on a representative sample of just over 20,000 in individuals over the age of 6, the overall seroprevalence was 13.9%, suggesting that tens of millions of Americans are infected with Toxocara. However, the seroprevalence was found to be considerably higher among non-Hispanic blacks and people living in poverty.
Based on the number of African Americans living in poverty in the US, we calculated that as many as 2.8 million have toxocariasis, making this disease one of the most common infections among any underrepresented minority groups.
In a separate study conducted in the 1990s, high rates of toxocariasis were also found among inner city Hispanic populations in Bridgeport and New Haven, Connecticut, especially among Puerto Rican immigrants. High rates of the infection were noted previously to occur in Puerto Rico.
Given its proposed links with asthma and developmental delays, human toxocariasis may represent a health disparity of staggering proportions, possibly associated with the high frequency of asthma and developmental delays noted among African Americans and some Hispanic groups living in poverty. The earlier association noted between toxocariasis and elevated lead levels observed in the HANES I study was confirmed in the NHANES III serum bank data, as was an interesting association between toxocariasis and co-infection with toxoplasmosis. The health and developmental impact of these co-factors also warrants further investigation.
Globally, high rates of toxocariasis has been noted in middle-income countries, with prevalence rates reaching 40% or higher in Indonesia and Brazil. Although there are few reported studies from low-income countries, it is of great interest to determine whether infection rates with Toxocara may exceed some of the better known human soil-transmitted helminth infections such as ascariasis, trichuriasis, or hookworm infection.