Antibodies to Roundworm Linked to Epilepsy

Pam Harrison

September 13, 2012

September 13, 2012 — The presence of antibodies to Toxocara canis, a roundworm in dogs, and Toxocara cati, a roundworm in cats, is higher in individuals with epilepsy than among controls, results of a systematic review and meta-analysis suggest.

Graziella Quattrocchi, MD, University of Catania, Italy, and colleagues found that the presence of anti-Toxocara species antibodies was higher among people with epilepsy in 7 case-control studies, although the association between epilepsy and seropositivity for Toxocara species was statistically significant in only 4 of the 7 studies included in the analysis.

"Epilepsy is the most prevalent neurologic condition today and it is more common in tropical areas, probably because of the presence of cases caused by infectious diseases largely absent in industrialized countries," senior author Pierre-Marie Preux, MD, PhD, University of Limoges School of Medicine, France, told Medscape Medical News.

"Considering that toxocariasis is a preventable disease, a better understanding of the relationship between toxocariasis and epilepsy may encourage improvement of programs on toxocariasis prevention in order to control both Toxocara spp. transmission and the related epilepsy burden," he said.

The study was published in the August issue of PLOS Neglected Tropical Diseases.

Prevalent Infection

Toxocariasis is one of the most prevalent zoonotic helminth infections worldwide, but it remains relatively unknown to the public, the researchers say. To raise awareness of the potential relationship between T canis and T cati infection and epilepsy, investigators carried out a systematic review and a meta-analysis of 7 case-control studies that included a total of 1867 participants: 850 case-patients and 1017 controls.

Two studies included a population aged 1 to 17 years, and 1 study excluded children 10 years of age and younger.

Studies were carried out in 6 different countries. All patients with epilepsy represented prevalent cases; controls were in- or outpatients attending the same hospital as case-patients, those going to the hospital for vaccinations or blood work, or volunteers. All controls were negative for a history of seizures.

"Toxocara spp. seropositivity ranged from 6.5% to 50.8% in the control group and from 12.0% to 59.7%" in patients with epilepsy, investigators reported; an association between epilepsy and infection was statistically significant in 4 of the 7 studies included in the review.

In a fifth study, a stronger and significant association was again observed between positivity for Toxocara species and epilepsy after adjustments were made for other variables.

A crude odds ratio ranging from 2.04 to 2.85 was also significant for the association between T canis and T cati infection and epilepsy, the authors add.

A meta-analysis was also done on all 7 studies. Here again, a significant common odds ratio of 1.92 between seropositivity for Toxocara species and epilepsy was estimated (P < .001).

In the 2 studies consisting of a juvenile population, a common odds ratio of 2.23 was also found (P = .002).

[T]he consistency of results between studies carried out in various countries and settings together with the plausibility and coherence with existing knowledge support the existence of a causal relationship between toxocariasis and epilepsy.

"In our paper, the consistency of results between studies carried out in various countries and settings together with the plausibility and coherence with existing knowledge support the existence of a causal relationship between toxocariasis and epilepsy," Dr. Preux said, "and further studies considering incident rather than prevalent epilepsy cases could permit us to demonstrate the existence of a temporal relationship between toxocariasis and epilepsy."

Accidental Hosts

Joseph Sirven, MD, Mayo Clinic Phoenix, Arizona, told Medscape Medical News that much of the focus on parasitic diseases and epilepsy is directed toward neurocysticercosis, the most common parasitic disease of the nervous system and the main cause of acquired epilepsy in developing countries.

As is the case with Toxocara species, the species causing neurocysticercosis are usually acquired via fecal-oral contact, in this instance with carriers of the adult tapeworm Taenia solium or by accidental ingestion of contaminated food.

"The number one cause of epilepsy outside the western world is…the Taenia solium tapeworm and humans are the accidental hosts of this worm because you get it from pork," he explained.

The main message about T solium transmission is that it is "completely preventable," he added. "All it takes is hand washing when dealing with pork or when cooking it, so it's all about hygiene and it's completely preventable."

In the same way, transmission of Toxocara species should also be completely preventable.

"This is the typical tape worm we think of in our pets who we should be vaccinating religiously to protect them from it," Dr. Sirven said. "So making sure your pets are vaccinated and practicing fastidious hygiene makes this infection completely preventable as well."

The authors and Dr. Sirven have disclosed no relevant financial relationships.

PLOS Negl Trop Dis. 2012;6:e1175. Full text