Playground Parasites and Infections

"We know in some cases it is linked to lower intelligence and epilepsy. So if you were to look at disadvantaged kids living in poverty who are also doing lower on tests of school performance, what percentage of that can be attributed to this worm?"
"Nobody is dying here. But it is potentially causing developmental delays that are affecting quality of life, and the economic impact is far greater. It could trap children in poverty."
"[Untreated, the infection could clear after months or even years] but we don't know for sure."
Dr. Peter Hotez, dean, National School of Tropical Medicine, Baylor College of Medicine, Houston, Texas

"What we don't see is easy to ignore."
"There isn't a story to wrap around it to make it emotionally salient."
Dr. Lance Erickson, sociology professor, Brigham Young University, Utah

"It's hard for people to accept that it could be having the effect that it is. We don't really know its impact, which is frustrating."
"These are larvae burrowing through the brain. It's not something that any mother or father of a child would welcome."
Dr. Celia Holland, parasitology professor, Trinity College Dublin, Ireland

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A parasitology professor at Trinity College Dublin, Celia Holland found that mice with Toxocara larvae in the brain experienced reduced learning ability with demonstrably less interest in exploration of its surroundings. "We had to terminate the experiments for ethical reasons because their locomotion started to be affected", she said of the impairment seen in mice with extreme infections caused by the presence of the larvae in their systems.

As for the larvae, they are a parasite, roundworms of the genus Toxocara. They live within the intestines of untreated cats and dogs, and most commonly make their homes in stray animals. Toxocara eggs are naturally shed in the feces of these animals, and they contaminate those places where the infected animals tend to be seen; in backyards, in playgrounds and in sandboxes.

Adult Toxocara roundworms stay in the small intestines of contaminated cats and canines. The eggs are excreted of their feces.  Credit Eye of Science/Science Source

When children frequent those places that are meant to entertain and inspire them to play and explore their surroundings, microscopic particles tend to cling to their hands. Children's hands frequently move toward their mouths, and once swallowed the eggs begin to hatch in the moist, warm receptive interior of a human. Larvae are released that make their way through the body. There is evidence that some of these larvae may reach the brain, with the result that cognition and learning become compromised.

Parasitic infections such as toxocariasis "likely account for a substantial yet hidden burden of mental illness in the United States", wrote Dr. Hotez in 2014, in a paper published in a mental health journal, JAMA Psychiatry. Two researchers at SUNY Downstate Medical Center in New York conducted a study to examine cognitive achievement correlated with Toxocara infection in people. It was published in the international Journal for Parasitology.

They discovered that the mean test scores, with the use of a cross-section of national data, were lower among children testing positive for Toxocara exposure, with another study published in 2015 finding a similar association in adults representing the investigative work of researchers at Brigham Young University in Provo, Utah.

The latest report by the U.S. National Health and Nutrition Examination Survey published in September in the journal Clinical Infectious Diseases, pointed out that roughly 5 percent of the population analogous to about 16 million people, carry Toxocara antibodies in their blood, revealing they had ingested roundworm eggs. This is a risk more common to poor neighbourhoods than to the general public in the United States.

Among African-Americans, as an example, the rate was closer to 7 percent, according to the Centers for Disease Control and Prevention. And for people living below the poverty line, the infection rate came in at ten percent. There has been little research conducted on the phenomenon, and Dr. Erickson points out that since the impairment produced by the infection is not severe in its presentation, no urgency is given to the need to research the phenomenon.

Dr. Hotez, on the other hand, speaks of Toxocara as one of the most common of parasitic infections and one of the most neglected by scientific enquiry. It is unknown how frequently ingested eggs go on to full blown infection, for example. And while studies reveal that pets receiving veterinary care rarely carry Toxocara, poorer neighbourhoods are home to a disproportionate number of strays most likely to carry roundworm.

Infections in humans can indeed progress from the mild symptoms of slight fever, fatigue, abdominal pain and cough, to Toxocara larvae entering eyes and causing blindness, or infecting the liver and lungs where damaging inflammatory reactions could result. If a child is taken to a pediatrician with the common symptoms of Toxocara infection, so common they could be mistaken for any number of illnesses, that Toxocara may be involved, rarely comes to mind for most doctors.

If its presence is, however, correctly detected and a diagnosis produced, it can be readily and effectively treated with the anti-parasitic drug albendazoic, according to Dr. Hotez.

A playground in the Bronx. Toxocara eggs or larvae had been present in 9 metropolis parks, together with three-quarters of these examined in the Bronx.   Credit Gregg Vigliotti for The New York Times