You are in: eMedicine Specialties > Infectious Diseases > MEDICAL TOPICS ToxocariasisArticle Last Updated: Jun 15, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 11
  Author: Sun Huh, MD, PhD, Chairman, Professor, Department of Parasitology, College of Medicine, Hallym University, Korea Coauthor(s): Sooung Lee, PhD, Department of Environmental and Tropical Medicine, College of Medicine, Konkuk University, Korea Editors: Pranatharthi Haran Chandrasekar, MD, Director of Infectious Disease Fellowship, Professor, Department of Internal Medicine, Harper Hospital, Wayne State University School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Gordon L Woods, MD, Consulting Staff, Department of Internal Medicine, University Medical Center; Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital; Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital Author and Editor Disclosure Synonyms and related keywords: dog roundworm, Toxocara canis, T. canis, cat roundworm, Toxocara cati, T. cati, covert toxocariasis, visceral larva migrans, ocular larva migrans, helminths, intestinal parasites, intestinal vermiform parasites. INTRODUCTIONSection 2 of 11
  BackgroundToxocariasis is an infection caused by the accidental ingestion of larvae of the dog roundworm Toxocara canis or the cat roundworm Toxocara cati. The soil of parks and playgrounds is commonly contaminated with the eggs of T canis, and infection may cause human disease in the liver, lung, muscle, eye, and brain. Three syndromes of Toxocara infection are generally recognized. In children, covert toxocariasis is a mild, subclinical, febrile illness. Symptoms can include cough, difficulty sleeping, abdominal pain, headaches, and behavioral problems. On examination, hepatomegaly, lymphadenitis, and wheezing can be present. Visceral larva migrans is caused by the migration of larvae through the internal organs of humans and the accompanying inflammatory reaction that results from this. A constellation of symptoms develops that includes fatigue, fever, cough, bronchospasm, abdominal pain, headaches, and, occasionally, seizures. On examination, hepatomegaly, lymphadenitis, and wheezing can be found. Occasionally, pleural effusions develop. Chronic urticaria has been described. Severe cases can lead to myocarditis or respiratory failure. Ocular larva migrans, which is caused by migration of larva into the posterior segment of the eye, tends to occur in older children and young adults. Patients may present with decreased vision, red eye, or leukokoria (white appearance of the pupil). Granulomas and chorioretinitis can be observed in the retina, especially at the macula. Unilateral visual loss, retinal fibrosis, and retinal detachment occur. Serum antibodies to Toxocara are often absent or present in low titers. Prevention is obviously preferable, but eradicating T canis is difficult because of the complexity of its life cycle. Diagnosis is difficult because confirmation of infection requires demonstration of larvae by biopsy. Therefore, clinicians use serologic testing (eg, enzyme-linked immunosorbent assay [ELISA], immunoblot) to infer diagnosis. Fortunately, for most patients the prognosis is very good. PathophysiologyAdult worms of the Toxocara species live in the small intestine of dogs and puppies and range from 4-12 cm in length. Almost all puppies are infected at or soon after birth. During the summer, in wet conditions, Toxocara eggs are embryonated in 2-5 weeks and become infective. They survive for years in the environment, and humans typically ingest the eggs by oral contact with contaminated hands. Once introduced into the human intestine, the eggs decorticate, releasing the larvae. The larval form is visible only under a microscope because it is less than 0.5 mm in length and 0.02 mm wide. The larvae penetrate the bowel wall and migrate through vessels to the muscles, liver, and lung and sometimes to the eye and brain as well. Disease severity depends not only on the number of larvae ingested but also on the degree of allergic reaction. Patients with atopy may experience more severe toxocariasis. The pathologic manifestations result from inflammation caused by the immune response directed against the excretory-secretory antigens of larvae. These antigens are released from their outer epicuticle coat, which is readily sloughed off when bound by specific antibodies. These antigens are a mix of glycoproteins, including a potent allergenic component named TBA-1. The inflammatory reaction causes epithelioid cells to surround each larva, and, subsequently, a dense fibrous capsule invests each granuloma. Although the main clinical manifestations are variable depending on the organs infected, the most common characteristic is chronic eosinophilia. Other typical findings follow according to the involved organs. With liver involvement, hepatomegaly, fever, and abdominal pain are common. With lung involvement, pulmonary symptoms (eg, dyspnea, cough, chest tightness), bronchospasm, interstitial pneumonitis, and, possibly, pleural effusion can be present. Ocular toxocariasis can induce decreased visual acuity, uveitis, retinal granuloma, endophthalmitis, and other ocular lesions that often lead to sudden vision loss in the affected eye. If the brain is involved, neurologic manifestations may occur, including seizures. Because the anti-Toxocara immunoglobulin-positive population is much higher than the prevalence of clinical toxocariasis, most patients are thought to have subclinical infection. In French adults, toxocariasis is termed common toxocariasis and is clinically characterized by the following:
In Irish children with high anti-Toxocara titers, the condition is termed subclinical toxocariasis, and the most frequent clinical findings are as follows:
Toxocariasis should be strongly considered when the patient has eosinophilia, characteristic clinical symptoms, and a positive finding on Toxocara serologic test. FrequencyUnited StatesNo nationwide data are available. In Cleveland, Ohio, seropositivity to T canis was reported in the cohort of children aged 2 and 12 years and in 12% of children aged 2, 3, and 4-10 years. InternationalToxocariasis is a worldwide infection. Seroepidemiological surveys show a 2-5% positive rate in healthy adults from urban Western countries and 14.2-37% in rural areas. In tropical countries, surveys show a positive rate of 63.2% in Bali, 86% in Saint Lucia (West Indies), and 92.8% in La Reunion (French Overseas Territories, Indian Ocean). Mortality/MorbidityToxocariasis is almost always a benign, asymptomatic, and self-limiting disease, although brain involvement can cause severe morbidity. Brain involvement can evoke meningitis, encephalitis, or epilepsy. Ocular involvement may cause loss of visual acuity or unilateral blindness. Pulmonary and hepatic forms can cause protracted symptoms if the patient does not receive treatment. RaceNo ethnic predilection is reported. SexNo predilection for either sex exists. AgeToxocariasis is most commonly a disease of children, typically children aged 2-7 years. Ocular toxocariasis occurs most often in older children and young adults. CLINICALSection 3 of 11
HistoryInquire about pets in the home. Ask if children play in a sandbox. Ask about pica and hand-washing practices, and determine if hygiene practices are poor. Symptoms during the acute phase may include the following:
Physical
Causes
DIFFERENTIALSSection 4 of 11
Hepatitis A
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Drug Name | Mebendazole (Vermox) |
|---|---|
| Description | DOC. Adverse effects are negligible, except headaches during early therapy. These symptoms are from metabolites secreted from nematodes that are killed by the drug. Causes worm death by selectively and irreversibly blocking uptake of glucose and other nutrients in susceptible adult intestines where helminths dwell. |
| Adult Dose | 25 mg/kg/d PO single dose for 4 wk |
| Pediatric Dose | <2 years: Not established >2 years: Administer as in adults |
| Contraindications | Documented hypersensitivity |
| Interactions | Carbamazepine and phenytoin may decrease effects; cimetidine may increase mebendazole levels |
| Pregnancy | C - Safety for use during pregnancy has not been established. |
| Precautions | Usually avoided in children <2 y; jaundice has been reported; adjust dose in hepatic impairment |
| Drug Name | Albendazole (Albenza) |
|---|---|
| Description | Second DOC if mebendazole is difficult to obtain. Decreases ATP production in the worm, causing energy depletion, immobilization, and, finally, death. |
| Adult Dose | 10 mg/kg/d PO single dose for 4 wk |
| Pediatric Dose | <2 years: Not established >2 years: Administer as in adults |
| Contraindications | Documented hypersensitivity |
| Interactions | Coadministration with carbamazepine may decrease efficacy; dexamethasone, cimetidine, and praziquantel may increase toxicity |
| Pregnancy | C - Safety for use during pregnancy has not been established. |
| Precautions | Contraindicated in first trimester; discontinue use if LFTs increase significantly (resume when levels decrease to pretest values) |
| Drug Name | Diethylcarbamazine citrate (Hetrazan) |
|---|---|
| Description | Synthetic organic compound highly specific for several common parasites. Does not contain any toxic metallic elements. Not recommended as the DOC because of more severe adverse effects. Recommended if therapy with mebendazole fails or mebendazole is not available. |
| Adult Dose | 3-4 mg/kg/d PO single dose for 4 wk |
| Pediatric Dose | <2 years: Not recommended >2 years: 3-4 mg/kg/d PO single dose for 4 wk |
| Contraindications | Documented hypersensitivity, children <2 y |
| Interactions | None reported |
| Pregnancy | C - Safety for use during pregnancy has not been established. |
| Precautions | Start at low dose (25 mg/d) and progressively increase dose to avoid adverse reactions due to parasite lysis |
| Media file 1: The image on the left is a chest radiograph (posteroanterior [PA]) of a patient with toxocariasis. The image on the right is a CT scan of the patient with toxocariasis showing multiple pulmonary nodules with surrounding ground-glass opacities at first visit. | |
 | View Full Size Image | Media type: X-RAY |
| Media file 2: Funduscopic examination of the right eye of a patient with ocular toxocariasis showing rhegmatogenous retinal detachment. | |
 | View Full Size Image | Media type: Photo |
Article Last Updated: Jun 15, 2006
