Toxocariasis
Toxocariasis is an infection caused by ingesting the eggs of nematode worms commonly found in dogs (Toxocara canis) and cats (Toxocara cati). Once ingested, these eggs hatch into larvae that can migrate through the body, affecting the liver, lungs, eyes, and other organs. While many infections remain asymptomatic, some individuals may experience symptoms like fever, cough, and abdominal pain. Diagnosis often occurs incidentally during routine medical exams, but can be confirmed through specific immunological tests or tissue biopsy.
Preventing Toxocariasis involves good hygiene practices, such as washing hands thoroughly and avoiding contact with contaminated soil, particularly in parks and playgrounds where pet feces may be present. Young children are at higher risk due to their habits of putting hands and objects in their mouths. Treatment typically includes medications like albendazole or mebendazole, and in severe cases involving organ damage, more intensive interventions may be necessary. As over 10,000 cases are reported annually in the United States, raising awareness about prevention and symptoms is crucial.
Toxocariasis
- ANATOMY OR SYSTEM AFFECTED: Eyes, gastrointestinal system, liver, lungs, respiratory system, vision
- ALSO KNOWN AS: Visceral larva migrans
Definition: an infection caused by ingesting the eggs of nematode worms that are normally found in dogs (as Toxocara canis) and cats (as Toxocara. cati).
In Toxocariasis, once the eggs of nematode worms have entered the human body, they hatch into larvae less than 0.5 millimeters (mm) long and 0.02 mm wide. The larvae then penetrate the walls of the digestive tract and commonly migrate to the liver, lungs, eyes, or anywhere the blood vessels are large enough to accommodate them. The presence of the worms may lead to serious infections such as myocarditis, encephalitis, or endophthalmitis. In the United States (US), more than 10,000 toxocariasis infections are reported annually. Almost 14 percent of the US population is infected with the Toxocara parasite at any given time.
Causes
Commonly occurring worms in dogs and cats lay eggs that are excreted in the feces of the animal. These eggs can survive in the environment for many years, so it is likely, for example, that the soil in many public parks and playgrounds is highly contaminated. Humans can ingest the eggs by touching their mouths with contaminated hands. Once ingested, the eggs release larvae that penetrate through the bowel and migrate throughout the body, including the liver, lungs, eyes, and brain.
Risk Factors
The risk of ingesting Toxocara eggs increases for people who live with or work with dogs or cats or who eat without thoroughly washing their hands after touching potentially contaminated soil or sand in a park, yard, or playground. Young children have a higher prevalence of infection because they tend to frequently put their hands or other objects, such as toys, in their mouths.
Symptoms
Toxocariasis is often asymptomatic, but some people experience fever, cough, abdominal pain, rash, or enlarged lymph nodes. Worm migration to the eyes can lead to vision disturbances, swelling around the eyes, or the appearance of a crossed eye.
Screening and Diagnosis
Most cases of toxocariasis go undiagnosed and do not cause problems or symptoms; however, cases are occasionally diagnosed during routine eye exams or through X-rays taken to diagnose other issues. Diagnosis of toxocariasis can be made by immunological testing and can be confirmed by the presence of larvae in tissue acquired during a tissue biopsy.
Treatment and Therapy
Toxocariasis is commonly treated with a five-day course of albendazole, a broad-spectrum anthelmintic, inhibiting the worms’ ability to eat glucose and thus causing the death of the worms. Mebendazole is another anthelmintic that may be used. Corticosteroids may be used to treat the symptomatic reactions of infestation. More serious complications, such as eye or organ involvement, may require surgery or chemotherapy.
Prevention and Outcomes
Toxocariasis can be prevented by keeping Toxocara eggs from entering the body by practicing good handwashing technique and by avoiding touching one’s face and mouth area with contaminated hands. Children should be prevented from touching their mouths, especially at parks or playgrounds, and from ingesting dirt. Many playgrounds and urban areas have posted signs that restrict dogs from areas where children play.
Bibliography
“About Toxocariasis.” CDC, 10 Sept. 2024, www.cdc.gov/toxocariasis/about/index.html. Accessed 11 Nov. 2024.
“Clinical Care of Toxocariasis - Parasites.” CDC, 9 Feb. 2024, www.cdc.gov/toxocariasis/hcp/clinical-care/index.html. Accessed 11 Nov. 2024.
Despommier, Dickson. “Toxocariasis: Clinical Aspects, Epidemiology, Medical Ecology, and Molecular Aspects.” Clinical Microbiology Reviews, vol. 16, 2003, pp. 265-72.
Huh, Sun. “Toxocariasis: Background, Pathophysiology, Epidemiology.” Medscape Reference, 10 Feb. 2023, emedicine.medscape.com/article/229855-overview?form=fpf. Accessed 11 Nov. 2024.
Marie, Chelsea, and William A. Petri. “Toxocariasis.” Merck Manuals, Sept. 2022, www.merckmanuals.com/professional/infectious-diseases/nematodes-roundworms/toxocariasis. Accessed 11 Nov. 2024.
Smith, Hazel, et al. “How Common Is Human Toxocariasis? Towards Standardizing Our Knowledge.” Trends in Parasitology, vol. 25, 2009, pp. 182-88.
“Toxocariasis: Symptoms & Causes.” Cleveland Clinic, 29 June 2022, my.clevelandclinic.org/health/diseases/23401-toxocariasis. Accessed 11 Nov. 2024.