1 in 5 People Worldwide Exposed to Toxocara

Human toxocariasis, a zoonotic tropical infection found around the world, does not always lead to symptoms or sickness. The infection is caused by parasitic roundworms carried by cats and dogs, putting pet owners at additional risk.

A study published in PLOS Neglected Tropical Diseases estimated the prevalence of toxocariasis in people worldwide, finding that about one-fifth of the world’s population carries antibodies against Toxocara.

Experts from universities in Iran, the United States, and Australia collaborated on a systematic review and meta-analysis study focusing on the prevalence of anti-Toxocara serum antibodies. While Toxocara infection prevalence has been studied in individual countries, there was little information on global infection estimates.

The investigators searched 5 international databases for seroprevalence studies published between January 1, 1980 and March 15, 2019. The study team then used random effects models to calculate the overall seroprevalence regionally and worldwide.

Initial review identified 12,911 potential articles. Of these articles, 371 were considered relevant to the study topic. After applying exclusion and inclusion criteria, 250 articles were retained. Most studies used enzyme-linked immunosorbent assay (ELISA) to detect anti-Toxocara antibodies.

The 250 eligible studies included 265,327 participants spanning 71 countries. The estimated global seroprevalence was 19% (95% confidence interval, 16.6-21.4%; 62,927/265,327).

Seroprevalence was lowest in the Eastern Mediterranean region (8.2%) and highest in the African region (37.7%). Pooled seroprevalence for other World Health Organization regions was 10.5% in Europe, 22.8% in America, 24.2% in the Western Pacific, and 34.1% in South-East Asia.

Higher seroprevalence was regionally associated with lower income level, lower latitude, lower human development index, higher temperature, and higher precipitation. Risk factors included living in a rural area, being male, being younger, close contact with dogs or cats, close contact with soil, consumption of raw meat, and drinking untreated water.

According to the investigators it was meaningful that approximately 1.4 billion people have been exposed to Toxocara and that seroprevalence varies regionally according to sociodemographic context. Prevalence also appeared to be increasing somewhat in recent years, but the increase was not statistically significant.

Practical measures suggested included strategic anthelminthic treatment of stray and pet dogs/cats, attentive removal of animal feces from soil in public places, and regular sterilization of sand and soil in children’s playgrounds.

“The prevalence rates estimated here could be the cause of many clinical sequelae (allergic, ocular, and neurologic disorders), suggesting a marked public health impact and a need to implement preventative and control strategies,” the study authors wrote.