Visceral Larva Migrans 

Updated: May 14, 2018
Author: Raymond D Pitetti, MD, MPH; Chief Editor: Russell W Steele, MD 



Several roundworm parasites found in domestic animals can infect humans. Parasites are usually found in the larval stages in human tissues and provoke the clinical condition referred to as larva migrans. Toxocara species, the ascarid of dogs and cats, is most commonly associated with larva migrans. Classic visceral larva migrans (VLM) typically occurs in preschool-aged children with a history of eating dirt. Children can present with severe infection and can suffer from seizures, myocarditis, and encephalitis. Death has also been reported in some cases.


Children contract Toxocara infections by ingesting embryonated eggs. The larvae hatch in the small intestine, invade the mucosa, and enter the portal system. The liver traps some larvae, but other larvae proceed to the lungs and the circulatory system, where they can disseminate to virtually every organ. In particular, the larvae often deposit in the liver, lungs, eye, heart, and brain. However, the parasite cannot complete its life cycle in humans. Larvae persist in tissues, provoking a granulomatous reaction and eventually dying. As a result, abscesses or granulomas form. Clinical manifestations depend on the tissue damage caused by the invading larvae and the associated immune-mediated inflammatory response.

See the image below.

Diagram of the Toxocara canis life cycle image. Co Diagram of the Toxocara canis life cycle image. Courtesy of the Centers for Disease Control and Prevention.



United States

The seroprevalence of Toxocara infection in children varies from 2-10%.


Although most reported cases occur in the United States, international incidence is likely similar or slightly higher.


Death is rare. Long-term morbidity is present with ocular larva migrans (ie, loss of vision in the affected eye) but not usually with visceral larva migrans. Chronic eosinophilic pneumonia, myocarditis, and Henoch-Schönlein purpura have been associated with visceral larva migrans.


Infection rates are higher among blacks and Hispanics, likely because of greater exposure to the parasite.


Visceral larva migrans has no sex predilection.


Infection primarily occurs in children aged 1-4 years but can occur at any age.




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  • Children with visceral larva migrans (VLM) may complain of loss of appetite, fever, cough, wheezing, or abdominal pain.

  • Ask parents about the presence of household pets and if the child is known to eat dirt.

  • Ascertain a careful history regarding occupational and household chemical exposures, drug exposures, asthma, atopic dermatitis, travel to tropical areas, or the consumption of raw meat.


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  • Children may have marked hepatomegaly and splenomegaly, wheezing, and rales.

  • Children may also have a pruritic rash or urticaria.[1] Guidelines for evaluation and management of urticaria in adults and children have been established.[2]

  • Periorbital edema and strabismus have also been seen in some children with visceral larva migrans.


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  • Toxocara canis is the most common cause of visceral larva migrans. Mature T canis worms live in the small intestines of dogs, their natural host. Heavily infected dogs can pass millions of eggs each day in their feces.[3]

  • Toxocara cati can also cause visceral larva migrans.

  • Other etiologic agents include Baylisascaris procyonis, Capillaria hepatica, Ascaris suum, and some Ancylostoma species.





Laboratory Studies

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  • A CBC count often reveals leukocytosis and eosinophilia in patients with visceral larva migrans (VLM); however, eosinophilia may not always be present. Children may be anemic.

  • Obtain stool cultures to rule out other parasitic infections.

  • Elevated titers of isohemagglutinins to the A and B blood group antigens support the diagnosis of visceral larva migrans.

  • Enzyme-linked immunosorbent assay (ELISA) is the most commonly used serologic test physicians use to diagnose visceral larva migrans, with a reported sensitivity of 78.3% and specificity of 92.3%. Positive results should be confirmed using Western blotting.

  • Hypergammaglobulinemia may be present.

Imaging Studies

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  • Children with visceral larva migrans may exhibit an abnormal liver parenchymal pattern on both abdominal ultrasonography and CT scanning.[4, 5]

  • MRI may reveal multiple cerebral lesions in patients with CNS visceral larva migrans.

  • Pulmonary infiltrates due to visceral larva migrans generally manifests as a transient form of Löffler syndrome or simple eosinophilic pneumonia on a chest radiograph.

A study described the characteristic radiologic findings of pulmonary toxocariasis on initial and follow-up chest CT. The study found that pulmonary toxocariasis manifested as multiple lesions in four radiologic patterns with subpleural and lower lung predominance on initial and follow-up CT. The study further reported that a linear opacity may be one of many clues in the diagnosis of pulmonary toxocariasis on CT.[6]


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  • In unusual circumstances, liver biopsy may aid in diagnosing visceral larva migrans; however, microscopic identification of larvae from biopsy samples is infrequent.

  • Negative liver biopsy findings do not exclude visceral larva migrans.

Histologic Findings

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  • Multiple eosinophilic abscesses and allergic-type granulomas are often found in affected tissues.



Medical Care

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  • Therapy in patients with visceral larva migrans (VLM) is aimed at relieving symptoms and is intended to diminish the host inflammatory response to the parasite. Corticosteroids and antihistamines are often used for this purpose. Patients with myocarditis or CNS disease should always be treated with corticosteroids.

  • Antiparasite agents, such as mebendazole, may help reduce symptoms; however, systemic treatment with anthelminthics can result in hypersensitivity reactions. Clinical trials have raised questions about their efficacy.

  • Attempt to identify the source of infection. Infected puppies and kittens should be treated with appropriate anthelminthic agents.


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  • Consider infectious diseases consultation in unusual or difficult cases.

  • Consider other consultations depending on the organ system involved.


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  • No special diet is necessary for acute treatment.

  • If children have a history of pica (eg, eating dirt, paint chips), attempts should be made to alter the behavior.


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  • No activity restrictions are required beyond that required for the treatment of the acute infection or its sequelae.



Medication Summary

Children can be treated with an anthelmintic agent. Severe infections should be treated with systemic corticosteroids.


Class Summary

Historically, the treatment of visceral larva migrans (VLM) in adults and children was primarily symptomatic. However, the identification of anthelmintics (eg, thiabendazole, diethylcarbamazine) in the 1960s offered an effective therapeutic choice. Anthelmintics act against the migrating larvae.

Parasite biochemical pathways are different from the human host; thus, toxicity is directed to the parasite, egg, or larvae. The mechanism of action varies within the drug class. Antiparasitic actions may include the following:

- Inhibition of microtubules causes irreversible block of glucose uptake

- Tubulin polymerization inhibition

- Depolarizing neuromuscular blockade

- Cholinesterase inhibition

- Increased cell membrane permeability, resulting in intracellular calcium loss

- Vacuolization of the schistosome tegument

- Increased cell membrane permeability to chloride ions via chloride channels alteration

Mebendazole (Vermox)

Selectively and irreversibly blocks the uptake of glucose and other nutrients in susceptible intestine-dwelling helminths.

Thiabendazole (Mintezol)

Inhibits mitochondrial formate reductase, which is specific for helminth.

Albendazole (Albenza)

Acts primarily by inhibiting tubulin polymerization, resulting in the loss of cytoplasmic microtubules. Tends to be most effective against larval forms.



Further Inpatient Care

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  • Children rarely require hospitalization for visceral larva migrans (VLM).


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  • Arrange transfer for children with disease that require services or specialists not readily available (unusual occurrence).


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  • Avoid contaminated areas when possible.


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  • Pneumonia

  • Seizures

  • Myocarditis

  • Encephalitis

  • Abscess

  • Decreased visual acuity and blindness

  • Death


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  • Visceral larva migrans is generally benign and self-limiting. However, serious sequelae can occur, resulting in significant risk of morbidity and mortality.

Patient Education

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  • Instruct caregiver to worm household pets and to properly dispose of pet feces.

  • Encourage good personal hygiene, including washing hands after playing with pets.

  • Encourage caregivers to prevent children from playing in areas that are soiled with pet or other animal feces.

  • Teach older children that eating dirt may be dangerous.