toxocara and children -- 4/25/18

Today's selection -- from This Is Your Brain on Parasites by Kathleen McAuliffe. The impact of roundworm on children:

"Toxocara is better known to pet owners as roundworm­ -- those pale yellow wriggling threads that dogs and cats sometimes cough up or that are passed in their stools along with thousands of the parasite's microscopic eggs. When the eggs are consumed by another dog or cat, they develop into fast-moving larvae that invade many dif­ferent organs of the body. Those that reach the gut hatch into worms and begin pumping out eggs, repeating the cycle. The infection is also passed down from one generation of animals to the next, for the larvae that stay behind in other tissues are activated when a female becomes pregnant, at which time they may cross her placenta or pass into her milk, invading her litter.

"Roundworms spread to other hosts in much the same way as T. gondii. The eggs may be picked up by rodents, rabbits, moles, birds, and other small creatures that in turn may appeal to canine or feline taste buds -- providing yet another route by which the parasite can get back to its spawning ground inside our pets' guts. Livestock can also consume the eggs, so people may become exposed to the larvae by eat­ing undercooked meat. The most common way we come in contact with the parasite, however, is by poor hygiene. Most vulnerable in that regard are young children playing in the dirt or in sandboxes contami­nated with cat or dog feces.

"When toxocara eggs hatch into larvae inside a human body, they do not grow into adult worms; that can happen only in a canine or fe­line host. Instead, the parasite's development remains arrested at its highly mobile larval stage, allowing it to wander far beyond the gut to organs such as the liver, lungs, eyes, and, occasionally -- no one knows how often, given the dearth of research -- the brain. In keeping with the parasite's reputation for being innocuous, blindness, seizures, and other severe neurological symptoms are uncommon complications of the infection. But starting as far back as the 1980s, clues began to surface in the medical literature that it might be destructive in more devi­ous ways.

"In an early study conducted by [professor of parasitology Celia] Holland and physician Mervyn Tay­lor in Ireland, two hundred children who had tested positive for the parasite were divided into three groups based on levels of antibodies (a measure of the severity of the infection). Behavioral disturbances, headaches, and disrupted sleep, along with twenty other physical symptoms ranging from asthma to stomach pain, all increased in di­rect proportion to the youngsters' antibody levels. Other small stud­ies -- including two carried out in the United States -- compared the cognitive skills of infected children with those free of it. Worse out­comes -- for instance, lower academic performance, hyperactivity, and heightened distractibility -- were reported in the infected children. And an epidemiological survey conducted in France -- the only one to Holland's knowledge that has focused on an older age group -- con­nected the infection to a higher risk of dementia.

"All these studies had only a few hundred subjects each, making it impossible to draw firm conclusions from them. What's more, toxo­cara disproportionately affects the poor, so socioeconomic factors muddied interpretation of the evidence. In short, this smattering of data, while concerning, was hardly persuasive.

"A study published in 2012, however, rigorously controlled for those confounding variables -- and it bore out Holland's suspicions. The re­port, which appeared in the International Journal for Parasitology, was based on an analysis of a huge body of epidemiological data collected in the United States by the CDC. ...

"The survey also revealed that toxocara's toll is far from evenly distributed among ethnic groups. Twenty-three percent of African American children were infected, in contrast to 13 percent of Mexican Americans and 11 percent of whites. This implies that disadvantaged minorities may do worse at school not only because of well-known factors like poor nutrition and inferior education but also, possibly, because of parasites in their heads -- or so believes Michael Walsh, an epidemiologist at the State University of New York, Downstate, in Brooklyn and the lead author of the study."



Kathleen McAuliffe


This Is Your Brain on Parasites: How Tiny Creatures Manipulate Our Behavior and Shape Society


First Mariner Books


Copyright 2016 by Kathleen McAuliffe


barns and noble booksellers
Support Independent Bookstores - Visit

All delanceyplace profits are donated to charity and support children’s literacy projects.


Sign in or create an account to comment