eMedicine Specialties > Pediatrics: General Medicine > Parasitology

Visceral Larva Migrans

Raymond D Pitetti, MD, MPH, Associate Professor, Department of Pediatrics, Division of Pediatric Emergency Medicine, University of Pittsburgh School of Medicine; Consulting Staff, University of Pittsburgh Physicians

Updated: May 22, 2009

Introduction

Background

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.

Pathophysiology

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.

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

Frequency

United States

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

International

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

Mortality/Morbidity

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.

Race

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

Sex

Visceral larva migrans has no sex predilection.

Age

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

Clinical

History

• 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.

Physical

• 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.

Causes

• 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.

Differential Diagnoses

Other Problems to Be Considered

Allergies
Eosinophilia-myalgia syndrome
Neoplasia
Other parasitic infections

Workup

Laboratory Studies

• 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%.
• Hypergammaglobulinemia may be present.

Imaging Studies

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

Procedures

• 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

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

Treatment

Medical Care

• 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.

Consultations

• Consider infectious diseases consultation in unusual or difficult cases.
• Consider other consultations depending on the organ system involved.

Diet

• 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.

Activity

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

Medication

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

Anthelmintics

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.

Dosing

Adult

100-200 mg PO bid pc for 5 d

Pediatric

<2 years: Not established
>2 years: 100 mg PO bid pc for 3 d

Interactions

Carbamazepine and phenytoin may decrease effects of mebendazole; cimetidine may increase mebendazole levels; increased absorption with food

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Adjust dose in hepatic impairment

Thiabendazole (Mintezol)

Inhibits mitochondrial formate reductase, which is specific for helminth.

Dosing

Adult

0.25-1.5 g PO bid pc for 7 d

Pediatric

50 mg/kg/d PO divided bid pc for 7 d

Interactions

May elevate serum levels of theophylline increasing toxicity (monitor serum levels and reduce dose prn)

Contraindications

Documented hypersensitivity; caution in children weighing <30 lb

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Closely monitor in hepatic or renal dysfunction; before initiating therapy, supportive therapy is necessary for anemic, dehydrated, or malnourished patients; use in confirmed worm infestation (not prophylactically); may cause nausea, vomiting, and mild CNS depression

Albendazole (Albenza)

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

Dosing

Adult

400 mg PO bid pc for 3-5 d

Pediatric

<2 years: 200 mg PO bid pc for 3-5 d
>2 years: Administer as in adults

Interactions

Coadministration with carbamazepine may decrease efficacy; dexamethasone, cimetidine, and praziquantel may increase toxicity

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Discontinue use if LFT results increase significantly (resume when levels decrease to pretest values); abdominal pain, nausea, vomiting, diarrhea, dizziness, vertigo, fever, increased intracranial pressure, and alopecia may occur; caution in patients receiving drugs with a narrow therapeutic index (monitor carefully)

Follow-up

Further Inpatient Care

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

Transfer

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

Deterrence/Prevention

• Avoid contaminated areas when possible.

Complications

• Pneumonia
• Seizures
• Myocarditis
• Encephalitis
• Decreased visual acuity and blindness
• Death

Prognosis

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

Patient Education

• 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.

Miscellaneous

Medicolegal Pitfalls

• Failure to recognize symptoms suggestive of visceral larva migrans (VLM)
• Initiation of extensive or invasive evaluation without considering this relatively common infection

Multimedia

Media file 1: Diagram of the Toxocara canis life cycle image. Courtesy of the Centers for Disease Control and Prevention.

References

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Keywords

visceral larva migrans, toxocariasis, Toxocara canis, Toxocara cati, VLM, parasitic infection, roundworm parasites, chronic eosinophilic pneumonia, myocarditis, Henoch-Schönlein purpura, eating dirt, ocular larva migrans, atopic dermatitis, asthma, hepatomegaly, splenomegaly, wheezing, rales, pruritic rash, urticaria, periorbital edema, strabismus, Löffler syndrome, seizure, abdominal pain, treatment, diagnosis

Contributor Information and Disclosures

Author

Raymond D Pitetti, MD, MPH, Associate Professor, Department of Pediatrics, Division of Pediatric Emergency Medicine, University of Pittsburgh School of Medicine; Consulting Staff, University of Pittsburgh Physicians
Raymond D Pitetti, MD, MPH is a member of the following medical societies: Allegheny County Medical Society, American Academy of Pediatrics, Pennsylvania Medical Society, and Society for Pediatric Research
Disclosure: Nothing to disclose.

Medical Editor

Robert W Tolan Jr, MD, Chief, Division of Allergy, Immunology and Infectious Diseases, The Children's Hospital at Saint Peter's University Hospital; Clinical Associate Professor of Pediatrics, Drexel University College of Medicine
Robert W Tolan Jr, MD is a member of the following medical societies: American Academy of Pediatrics, American Medical Association, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, Phi Beta Kappa, and Physicians for Social Responsibility
Disclosure: GlaxoSmithKline Honoraria Speaking and teaching; MedImmune Honoraria Speaking and teaching; Merck Honoraria Speaking and teaching; sanofi pasteur Honoraria Speaking and teaching; Baxter Healthcare Honoraria Speaking and teaching

Pharmacy Editor

Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine
Disclosure: Pfizer Inc Stock Investment from financial planner; Avanir Pharma Stock Investment from financial planner ; WebMD Salary and stock Employment and investment from financial planner

Managing Editor

Leslie L Barton, MD, Professor, Program Director, Department of Pediatrics, University of Arizona School of Medicine
Leslie L Barton, MD is a member of the following medical societies: American Academy of Pediatrics, Association of Pediatric Program Directors, Infectious Diseases Society of America, and Pediatric Infectious Diseases Society
Disclosure: Nothing to disclose.

CME Editor

Daniel Rauch, MD, FAAP, Director, Pediatric Hospitalist Program, Associate Professor, Department of Pediatrics, New York University School of Medicine
Daniel Rauch, MD, FAAP is a member of the following medical societies: Ambulatory Pediatric Association, American Academy of Pediatrics, and Society of Hospital Medicine
Disclosure: Baxter Honoraria Consulting

Chief Editor

Russell W Steele, MD, Head, Division of Pediatric Infectious Diseases, Ochsner Children's Health Center; Clinical Professor, Department of Pediatrics, Tulane University School of Medicine
Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, and Southern Medical Association
Disclosure: None None None

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