Toxocariasis (Human Roundworm Infection)

DigestiveDiseasesMeongsiljang Veterinary Advisory Board

Toxocariasis is a zoonotic parasitic disease caused by roundworm eggs from dogs and cats entering the human body and invading organs or the eyes. Children and pet owners should be especially cautious.

What is Toxocariasis?

An illustration explaining how roundworms in dogs can infect humans

Toxocariasis is a zoonotic parasitic disease caused by the ingestion of Toxocara canis or Toxocara cati eggs from dogs or cats, which can then migrate to and affect human organs or eyes. Early recognition is key. Children aged 2 to 7 and pet owners are at higher risk, but most cases can be prevented simply by washing hands after playing in sand and keeping up with regular deworming for pets. If symptoms such as fever, coughing, or vision changes recur, toxocariasis should always be considered as a possible cause.

How is it transmitted to humans?

Humans can become infected in only one way: by accidentally swallowing mature, infective roundworm eggs. Eggs passed in dog or cat feces need about a week in soil, sand, or grass to become infectious, and they can survive in this state for months to years. Infection occurs when a child puts their hands in their mouth after playing in sand, or eats unwashed vegetables or fruit. It’s also risky to let a dog lick you directly or to eat food after touching a dog’s fur. In humans, the larvae remain in the larval stage and do not mature into adult worms, so direct person-to-person transmission does not occur.

Main symptoms in humans

The symptoms vary significantly depending on which organs the larvae migrate to. - Visceral larva migrans: Larvae migrate to the liver and lungs, causing fever, coughing, hepatomegaly, and abdominal pain. - Ocular larva migrans: Vision loss, strabismus, and eye pain occur in one eye, potentially leading to blindness in severe cases. - Neural larva migrans: Neurological symptoms such as headaches, seizures, and behavioral changes rarely occur. - Asymptomatic infection: In adults, it is common to have no symptoms other than elevated blood eosinophil counts. If your child experiences unexplained recurrent fever and coughing and has frequent contact with pets, be sure to mention this to your veterinarian.

A checklist image showing the classification of toxocariasis symptoms

Visit a hospital immediately if you have these symptoms

If you or your child have any of the following symptoms and have been in contact with a pet, please visit a nearby internal medicine, pediatrics, or ophthalmology clinic immediately. These symptoms include sudden vision loss in one eye or the development of strabismus, unexplained high fever lasting more than two weeks, recurrent dry cough and wheezing, or seizures and changes in consciousness. Ocular symptoms require prompt attention, as delays can lead to permanent vision damage, making the first few hours critical.

How is it diagnosed at the hospital?

Toxocariasis cannot be diagnosed through fecal examination because the larvae remain in the human body in their larval stage and do not produce eggs. There are three main types of tests used for diagnosis: - Serum antibody test (ELISA): The most basic test, used to determine infection status and monitor progression. - Blood test: An increase in eosinophils in the blood is an important clue that may suggest infection. - Imaging tests: Abdominal ultrasound, CT scans, and fundoscopic examinations help identify the location of lesions. According to veterinary parasitology textbooks, while serum testing is useful, a positive antibody result may indicate past infection. Therefore, it is important to consider symptoms, blood test results, and imaging findings together.

How is treatment carried out?

The treatment approach depends on which organs are affected and the severity of symptoms. - Asymptomatic or mild cases: Often managed with observation alone. Since humans are not definitive hosts, the larvae cannot mature into adult worms; however, the larvae themselves can persist in tissues for years, so we monitor for any changes in symptoms. - Visceral larva migrans: Treated with anthelmintics (albendazole class) for several days to weeks. - Ocular larva migrans: Treated with anthelmintics combined with steroids; surgical intervention is required if there is significant retinal damage. - Neural larva migrans: Managed with hospitalization, combining anthelmintic and anti-inflammatory treatments. The exact dosage and duration of treatment are determined by the attending physician based on the patient’s weight and symptoms.

An illustration showing the stages of treatment for toxocariasis

Preventive measures to practice at home

Here are some preventive measures you can follow at home: - Regular deworming for pets: Puppies should be dewormed at 2, 4, 6, and 8 weeks of age, then monthly until they are 6 months old, and thereafter 2 to 4 times a year. - Deworming for pregnant and nursing dogs: Pregnant and nursing dogs should also be dewormed as directed by a veterinarian. - Prompt cleanup of feces: Clean up feces from yards and walking paths immediately, and wash your hands afterward. - Hand hygiene: Always wash your hands with soap for 30 seconds after handling pets or touching soil or sand. - Washing after children play in sand: Teach children not to put their hands in their mouths after playing in sand. - Thorough washing of vegetables and fruits: Rinse them well under running water. In households where pets are properly dewormed, the risk of human infection is significantly reduced.

Children, pregnant women, and immunocompromised individuals should be extra cautious

Children aged 2 to 7 are at higher risk of visceral larva migrans because they often swallow soil-borne eggs repeatedly due to habits like playing in sand and putting their hands in their mouths. In humans, ocular larva migrans, where larvae migrate to the eyes, is also not uncommon. Pregnant women should strictly follow preventive guidelines, as treatment options may be limited if they become infected. Individuals undergoing chemotherapy or with compromised immune systems are at risk of severe progression even from asymptomatic infections, so if you’ve recently brought a new puppy home, please have it checked for parasites at a veterinary clinic first.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Is it safe if I don’t directly touch my dog’s feces?

Not at all. Eggs can adhere to soil, dust, and grass, surviving for months to even years, so infection can occur through indirect contact alone. Prompt removal of feces and thorough handwashing are key.

My dog has roundworms, and I kissed him. Will I get infected right away?

Infection doesn’t occur immediately. Eggs freshly passed in a puppy’s feces need about a week in soil or manure to mature and become infectious. However, if a puppy ingests eggs clinging to its fur or around the anus, infection can occur. Wash your hands and mouth immediately, and start deworming right away.

Can it be transmitted between people?

It is not transmitted from person to person. This is because the larvae only exist in the human body and do not lay eggs.

The blood test showed a positive antibody result. Is treatment really necessary?

If there are no symptoms and eosinophil counts and imaging results are normal, it’s likely a past infection, so treatment may not be started right away. Be sure to work with your veterinarian to establish a follow-up monitoring plan.

How often should I deworm my dog?

For puppies, deworming is typically done at 2, 4, 6, and 8 weeks of age, then once a month until they reach 6 months old. For adult dogs, the standard is 2 to 4 times a year (every 3 to 6 months). If you live with children, pregnant women, or immunocompromised individuals, we recommend deworming four times a year (quarterly).

Can You Trust Online Pet Food Grading Charts? — A Veterinarian’s Real Selection Criteria for 2026

My Senior Cat Won’t Eat — A Complete Guide to Choosing Food for Cats with Weak Digestion

Royal Canin vs Hill’s vs Purina vs Orijen — Which Brand Is Right for Your Pet, According to Veterinarians?

If Your Cat’s Behavior Seems Off — Symptoms, Diagnosis, and Treatment Timing for Pituitary Tumors

Sudden Blood Pressure Abnormalities in Cats — Symptoms and Treatment of Feline Pheochromocytoma (Chromaffin Cell Tumor)

My Cat Is Constantly Lethargic and Having Seizures — Causes and Treatment Timing for Neoplasm-Induced Hypoglycemia

Is Your Cat’s Weight Gain a Path to Diabetes? — Causes and Management of Obesity and Insulin Resistance

When Your Cat Keeps Stumbling — Suspected Insulinoma Symptoms and When to Visit the Vet

Complete Guide to Feline Insulin Injections and Dosage — Including Critical Hypoglycemia Warning Signs

If Your Cat Keeps Having Seizures — Warning Signs of Hypoparathyroidism and Hypocalcemia

References

[1] Bowman DD, Georgi JR. Georgis' Parasitology for Veterinarians, 9th ed., Saunders/Elsevier, 2009

[2] Lee AC, Schantz PM, Kazacos KR et al. Epidemiologic and zoonotic aspects of ascarid infections in dogs and cats. Trends in Parasitology 26: 155–161, 2010

[3] Schantz PM. Larva migrans syndromes caused by Toxocara species and other helminths. In: Infectious diseases, W.B. Saunders, 2004

[4] Glickman LT, Schantz PM. Epidemiology and pathogenesis of zoonotic toxocariasis, 1981

[5] CDC Guidelines for veterinarians: Prevention of zoonotic transmission of ascarids and hookworms