Human Toxocariasis Widespread, Preventive Interventions Needed

By Marilynn Larkin

December 24, 2019

NEW YORK (Reuters Health) - Human toxocariasis (HT), a zoonotic disease affecting close to one-fifth of the world's population, deserves increased attention, a systematic review and meta-analysis suggests.

"HT is associated with several clinical syndromes," Dr. Ali Rostami of Babol University of Medical Sciences in Iran told Reuters Health by email. "In addition to specific symptoms, including visceral larva migrans, ocular larva migrans, and covert/common toxocariasis (CT), toxocariasis can precipitate some non-specific complications, including neurological and psychiatric or cardiac, allergic skin disorders and/or asthma."

"The CT form of toxocariasis is especially interesting, because of its potential role in asthma or developmental delays in socioeconomically disadvantaged children, although its likely role is often ignored by many physicians," he said. "Our results suggest that at least in areas with high prevalence rates of infection, physicians should consider Toxocara infection as a potential cause of the above-mentioned complications."

"Moreover," he added, "our analysis finds that toxocariasis may in fact represent one of the commonest neglected tropical diseases of people who live in extreme poverty."

Dr. Rostami and colleagues searched the literature from 1980-2019 to calculate the prevalence of anti-Toxocara serum antibodies (T-seroprevalence) in all six World Health Organization regions and worldwide.

They identified 250 eligible studies (253 datasets) including 265,327 people in 71 countries.

As reported in PLoS Neglected Tropical Diseases, the estimated global T-seroprevalence rate was 19%, with the highest in Africa (37.7%) and lowest in the Eastern Mediterranean (8.2%). The pooled seroprevalence for other WHO regions was 34.1% in South-East Asia; 24.2% in the Western Pacific; 22.8% in the Americas; and 10.5% (8.5-12.8%) in Europe.

Lower income level, lower human development index, lower latitude, higher humidity, higher temperature, and higher precipitation were all associated with a significantly higher T-seroprevalence.

Potential risk factors associated with seropositivity to Toxocara included male gender; living in a rural area; young age; close contact with dogs, cats or soil; consumption of raw meat; and drinking untreated water.

Dr. Rostami said, "To our knowledge, there is no country that has appropriate preventive initiatives in place, even though the disease could be treated and prevented through relatively simple and straightforward methods."

"In other studies by our team, it was estimated that about 12% of public places - including parks and children's playgrounds - in the U.S. are contaminated with Toxocara eggs," he noted. "The implications are that toxocariasis may represent one of the commonest neglected infections of poverty-stricken regions in the U.S., especially among underrepresented minority children and those in the Southern U.S."

He added that Senator Cory Booker (D-NJ) has submitted legislation in the U.S. Senate to begin addressing toxocariasis and other neglected diseases. (

Dr. Louis Weiss, professor of pathology and of medicine at Albert Einstein College of Medicine in New York City and co-director of the Einstein Global Health Center, commented by email, "This survey provides excellent evidence on the prevalence of infection. A similar meta-analysis of the rates of symptomatic infection would be useful, (as would) improved therapy."

Clinicians should be advising patients to wash hands after contact with soil and not drink untreated surface water (as opposed to tap or bottled water), he told Reuters Health. "Provide veterinary care to cats and dogs, and keep outdoor sandboxes covered to prevent use by feral cats."

"While about 20% of patients have evidence of exposure (seropositivity)," he added, "the vast majority of these individuals do not have symptomatic infection."

Dr. Aaron Glatt, chair of medicine at Mount Sinai South Nassau in Oceanside, New York, commented in an email to Reuters Health, "Clinicians need to be constantly aware of the potential manifestations and presentations that result from Toxocara exposure." Like Dr. Weiss, he noted, "the best way to prevent illness in the U.S. is by making sure pets are taken to the veterinarian and given appropriate preventive care, such as testing and treatment plans for deworming."

"The Centers for Disease Control and Prevention recommends washing hands with soap and water after playing with pets or other animals, after outdoor activities, and before handling food or eating," he added.

SOURCE: PLoS Neglected Tropical Diseases, online December 19, 2019.