Toxocariasis is an infection caused by the roundworms (nematodes) Toxocara canis and Toxocara cati, which are parasites that usually infect animals.
People, especially young children, can become infected when they eat soil contaminated with animal stool (feces) that contains the roundworm eggs.
The infection may cause fever, cough or wheezing, and an enlarged liver and, in some people, it may cause vision problems.
Doctors confirm the diagnosis by identifying antibodies to the roundworm in a sample of blood.
Treatment is usually unnecessary but may include medications used to treat worm infections and corticosteroids.
Regularly deworming dogs and cats and washing hands can help prevent the infection.
Helminths are parasitic worms that can infect humans and animals. There are 3 types of helminths: flukes (trematodes), tapeworms (cestodes), and roundworms (nematodes). Toxocara, Toxocara canis, and Toxocara cati are roundworms.
Toxocariasis infection occurs mainly in young children, who ingest Toxocara eggs by eating soil, dirt, or sand that is contaminated by the stool (feces) of dogs, cats, or other animals that carry the parasite. Sandboxes, where dogs and cats often defecate and children often play, pose a particular hazard for exposure to the eggs. Children frequently unknowingly transfer the eggs from their hands to their mouth and may eat the contaminated sand.
Occasionally, adults ingest eggs when they touch contaminated soil or dirt, other contaminated surfaces, or others' unwashed hands and become infected.
People who regularly eat things that are not food, such as soil, dirt, or clay (an eating disorder called pica), are at particular risk of toxocariasis.
Rarely, people are infected by eating raw or undercooked meat of other infected animals such as rabbits and ducks.
(See also Overview of Parasitic Infections.)
Transmission of Toxocariasis
After infected animals pass Toxocara eggs in their stool (feces), the eggs mature in the environment and become able to cause infection.
The infected eggs can get into peoples' mouths through contaminated dirt or unwashed hands. After people swallow the infectious eggs, larvae hatch in the intestine. The larvae penetrate the intestinal wall and spread through the bloodstream. Once in the bloodstream, the larvae travel to various tissues in the body (such as the liver, heart, lungs, brain, or eyes) causing damage and inflammation.
The larvae do not mature to adult worms in people, but they can remain alive in the body for many months. The larvae mature to adult worms when they live in dogs or cats.
Toxocara eggs may be ingested by other animals, such as rabbits, ducks, or sheep. In these animals, the eggs hatch into larvae, which penetrate the wall of the intestine and travel to various tissues where they form cysts. Rarely, people are infected by eating raw or undercooked meat from these animals and ingesting the cysts.
Image from the Centers for Disease Control and Prevention, Global Health, Division of Parasitic Diseases and Malaria.
Symptoms of Toxocariasis
Toxocariasis symptoms may start within several weeks after eggs are ingested. They vary depending on the organ affected.
When larvae infect the soft internal organs (called visceral larva migrans), the most common symptoms are fever, cough or wheezing, and liver enlargement. Some people have a rash, spleen enlargement, or inflammation of the lungs. They may lose their appetite.
When larvae infect the eye (called ocular larva migrans), they typically cause no symptoms or very mild symptoms. Usually only 1 eye is affected. However, the eye may become inflamed, and vision may be impaired or lost.
Diagnosis of Toxocariasis
Blood tests to detect antibodies to the parasite
A doctor may suspect toxocariasis in a person who has an enlarged liver, inflammation of the lungs, a fever, and high levels of eosinophils (a type of white blood cell) in their blood.
The diagnosis of toxocariasis is confirmed by identifying Toxocara antibodies in the blood. (Antibodies are proteins produced by the immune system to help defend against infection, including by parasites.)
Rarely, a sample of the liver or another infected tissue is obtained and examined (biopsied) for evidence of larvae or inflammation resulting from their presence.
Treatment of Toxocariasis
If needed, medications used to eliminate worms (anthelmintics) and sometimes corticosteroids
Sometimes laser photocoagulation or other surgery when an eye is infected
In most people with toxocariasis, the infection goes away on its own, and treatment is unnecessary.
When symptoms are moderate to severe, doctors give albendazole or mebendazole. These medications are known as anthelmintics, and they are taken by mouth.
When symptoms are severe, doctors may give corticosteroids to reduce inflammation.
People who have ocular larva migrans should be treated by an eye specialist. They are given 2 types of corticosteroids: 1 that is taken by mouth and 1 that is applied directly to the infected eye. Even with appropriate care, most people have some loss of vision.
Occasionally, laser photocoagulation (in which a laser beam is aimed into the back of the eye at the retina) is used to kill larvae in the eyes. Sometimes, doctors use cold probes (cryosurgery) to freeze areas of the eye or do other types of eye surgery to fix problems caused by toxocariasis.
Prevention of Toxocariasis
Prevention involves regularly doing the following:
Treating dogs for roundworms and treating cats for roundworms (deworming)
Washing hands with soap and water after playing with pets or other animals, after disposing of pet waste, after outdoor activities, and before handling food or eating
Covering sandboxes when not in use to prevent animals from defecating in them
Telling children to not eat dirt, soil, or clay
