Parents tend to be concerned about their kids’ well-being, from their smartphone use to whether or not their schools address their needs. But a recent New York Times article spiked anxieties about a completely unfamiliar source of worry for most American parents: parasites. Toxocara, a variety of roundworms commonly found in stray dogs and cats, has been discovered in the sandboxes of New York City playgrounds, most often playgrounds found in low-income neighborhoods. A report published in the journal Clinical Infectious Diseases “estimated that about 5 percent of the United States population — or about 16 million people — carry Toxocara antibodies in their blood, a sign they have ingested the eggs.” If children are infected, they may potentially suffer from learning disabilities and other ailments as a result. How worried do parents need to be?

Toxocara enter humans when someone, typically a child, eats or plays with dirt that contains the eggs (or, less commonly, eats undercooked meat). The eggs are spread by dog and cat feces. (Although there was a memorable case of an Australian woman who routinely ate graveyard dirt. In the process she apparently consumed beetles and other intermediate worm hosts.) Domestic dogs are routinely treated, so stray or untreated dogs are the biggest source of eggs. The eggs hatch, and the larva enter the bloodstream where they disperse throughout the body. It is rare that the worms complete their lifecycle in a human; infection with adult worms is rare. The worms typically cause symptoms consistent with a mild infection, but occasionally severe illness results. Infected children are generally not outwardly sick and toxocara infection goes unnoticed.

So how prevalent is it? The worms are everywhere, but as with many public health issues, socioeconomic status has a huge influence on risk. A study from Northern Spain found that middle class children had virtually no contact with toxocara before age 5. Among disadvantaged children, on the other hand, 37% of children under age 5 had antibodies to toxocara, indicating exposure to the worms. A whopping 65% of disadvantaged children over age 5 had been exposed. The reasons for this vast difference are unclear, but one possibility is that disadvantaged children have more exposure to untreated pets and reduced access to sanitary facilities.

There is also evidence of a rural-urban divide in toxocara exposure, at least in China. A study from Chengdu, a city in the Southern-central province of Sichuan, found considerably higher incidence of prior infection among rural children compared to their urban counterparts. The main reason seems to be that there are a lot more pet dogs in the rural areas. These findings may not be identical to a more dog-friendly urban culture like the United States.

The more recent research suggests that the parasite can reach the brain, with unknown long-term impacts. The good news is that most parents living in sanitary environments really don’t need to worry about toxocariasis. The bad news is that toxocara may be yet another obstacle placed in front of disadvantaged children.