OVERVIEW: What every clinician needs to know
Parasite name and classification
Toxocara canis and Toxocara cati are roundworms that normally infect dogs and cats; however, humans can be accidental hosts, resulting in visceral or ocular larva migrans. Other causative roundworms include species of Gnathostoma and Ancylostoma. Other roundworms, including the hookworm species Ancylostoma braziliense and Ancylostoma caninum, can cause cutaneous larva migrans in humans.
What is the best treatment?
For visceral larva migrans:
Mild cases may be self-limited without treatment or require only symptomatic treatment with antihistamines.
Albendazole 400 mg orally twice daily x 5 days
May add prednisone 1.0 mg/kg/day in severe cases
For ocular larva migrans:
No strong evidence that anti-parasitic drugs offer additional benefit over steroids alone, which should be the mainstay of therapy.
Prednisone 1.0 mg/kg/day for 14 days, then tapered
Albendazole 800 mg orally twice daily for 14 days
For cutaneous larva migrans:
Ivermectin 200 mcg/kg orally once OR
Albendazole 400 mg orally 3-7 days
What are the clinical manifestations of infection with this organism?
Visceral larva migrans may result in pneumonitis, hepatitis, and cutaneous lesions because of migration of the larvae.
Systemic symptoms may include fatigue, fever, nausea, abdominal pain, anorexia, wheezing, dyspnea, and cough.
Central nervous system (CNS) manifestations include cranial nerve palsies, altered mental status, and seizures.
Symptoms of ocular larva migrans include unilateral vision compromise.
Cutaneous larva migrans result in highly pruritic lesions at the site of entry, usually on the lower extremities. These include initial papules followed by serpiginous skin lesions.
Exam findings in visceral larva migrans may include hepatosplenomegaly and hepatic nodules, rales on chest exam, neurologic abnormalities, and pruritic cutaneous nodules.
Patients with ocular larva migrans have abnormal ophthalmologic exam findings, which can include endophthalmitis, uveitis, or retinal detachment.
Cutaneous larva migrans cause papular and serpiginous pruritic skin lesions most commonly on the lower extremities. However, nodules or bullae can occasionally be seen.
Do other diseases mimic its manifestations?
Visceral larva migrans in children can cause wheezing, pulmonary infiltrates, and eosinophilia, which can be mistaken for asthma.
The pulmonary infiltrates may also resemble tumor metastases.
Ocular larva migrans can result in eye findings similar to other infectious causes or, in some cases, retinoblastoma
The presentation of cutaneous larva migrans is fairly characteristic, although Strongyloides can produce similar skin lesions.
What laboratory studies should you order and what should you expect to find?
Results consistent with the diagnosis:
In visceral larva migrans, eosinophilia is seen in about one-third of all cases.
Hypergammaglobulinemia is also seen.
In CNS manifestations of visceral larva migrans, there can be cerebrospinal fluid (CSF) eosinophilia.
In cutaneous larva migrans, there is usually no eosinophilia.
Hepatic involvement in visceral larva migrans may lead to elevated transaminases.
Results that confirm the diagnosis
For visceral larva migrans, the diagnosis is made in the appropriate clinical setting and can be confirmed with an enzyme-linked immunosorbent assay (ELISA) IgG assay to Toxocara antigen available from the Centers for Disease Control and Prevention.
The ELISA cannot distinguish active from past disease. This requires clinical assessment.
Diagnosis can also be confirmed with tissue biopsy to evaluate for larvae, but this is almost never done in practice.
For ocular larva migrans, the diagnosis relies primarily on the ophthalmologic exam.
There are assays for anti-Toxocara IgG in the aqueous humor. A ratio to serum antibody greater than 3.0 is diagnostic.
Cutaneous larva migrans is a clinical diagnosis.
Stool studies are not helpful in the diagnoses of any of these conditions.
What imaging studies will be helpful in making or excluding the diagnosis?
A chest x-ray may show peribronchial or parenchymal infiltrates in visceral larva migrans ($).
CT of the lung may also be done to evaluate for these findings ($$).
Hepatic ultrasound may reveal nodules ($$).
MRI may be helpful in CNS manifestations ($$$$).
MRI may also be needed in ocular larva migrans ($$$$).
Imaging is not helpful for cutaneous larva migrans.
($ = 60-125, $$ 125-500, $$$ 500-1,000, $$$$ > 1,000)
What complications can be associated with this parasitic infection, and are there additional treatments that can help to alleviate these complications?
Severe disease burden in visceral larva migrans, especially in the myocardium or CNS may result in death, but this is rare.
There have been investigations regarding whether pulmonary involvement with visceral larva migrans may be associated with an increased risk of asthma, but the data are inconclusive.
Ocular larva migrans may result in retinal detachment and blindness.
Cutaneous larva migrans can lead to secondary bacterial infections of the lesions or the excoriations caused by scratching in response to severe pruritus.
What is the life cycle of the parasite, and how does the life cycle explain infection in humans?
Parasite Life cycle
For Toxocara species, which cause visceral and ocular larva migrans, the definitive hosts are usually dogs and cats.
They occur worldwide, with increased cases in tropical and rural areas, and there is an association with poverty.
Eggs are shed in the stool and then embryonate in the soil after 3 weeks. This is the infectious stage.
If ingested by dogs or cats, the eggs hatch and the larvae migrate through the gut, through the bronchial tree, and are coughed up and swallowed back into the gastrointestinal (GI) tract, where they mature into adult worms and reside in the small intestine, shedding eggs to repeat the cycle.
The embryonated eggs may also be ingested by smaller animals, then hatch, and the larvae encyst in muscle and can complete the cycle above if eaten by a dog or cat.
In humans who ingest soil contaminated with eggs (usually children), the eggs hatch and migrate through the gut wall to tissues in which they cannot mature further, but elicit the host inflammatory response that causes the clinical disease manifestations.
The life cycle of the Ancyclostoma species that cause cutaneous larva migrans are those of hookworm. They usually remain cutaneous, with pulmonary involvement rarely occurring.
For visceral larva migrans, ocular larva migrans, and cutaneous larva migrans, control is primarily related to keeping cat and dog feces disposed of properly.
Treatment of pets to reduce burden of infection is also helpful.
Minimizing oral exposure to soil, especially of children, through hand washing and other precautions is important for prevention of visceral larva migrans and ocular larva migrans.
Minimizing skin exposure to potentially contaminated soil, such as by not walking barefoot, is important for prevention of cutaneous larva migrans.
How does this organism cause disease?
The ability of Toxocara eggs to remain viable in the soil for months to years increases its prevalence.
If migrating through tissues, it provokes a strong immune response with resultant eosinophilia. However, this diminishes if the organisms become encysted in muscle or mature to adult worms in the intestinal lumen.
WHAT’S THE EVIDENCE for specific management and treatment recommendations?
Feldmeier, H, Schuster, A. “Mini review: Hookworm-related cutaneous larva migrans”. Eur J Clin Microbiol Infect Dis. vol. 31. 2012. pp. 915-8. (This is a review of cutaneous larva migrans.)
Pinelli, E, Herremans, T, Harms, MG, Hoek, D, Kortbeek, LM. “Toxocara and Ascaris seropositivity among patients suspected of visceral and ocular larva migrans in the Netherlands: trends from 1998 to 2009”. Eur J Clin Microbiol Infect Dis. vol. 30. 2011. pp. 873-9. (This source reports on surveillance for causative agents of visceral or ocular larva migrans in the Netherlands.)
Rubinsky-Elefant, G, Hirata, CE, Yamamoto, JH, Ferreira, MU. “Human toxocariasis: diagnosis, worldwide seroprevalences and clinical expression of the systemic and ocular forms”. Ann Trop Med Parasitol. vol. 104. 2010. pp. 3-23. (This source is a good general overview of the epidemiology and clinical management of human infections with Toxocara species.)
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- OVERVIEW: What every clinician needs to know
- Parasite name and classification
- What is the best treatment?
- What are the clinical manifestations of infection with this organism?
- Do other diseases mimic its manifestations?
- What laboratory studies should you order and what should you expect to find?
- What imaging studies will be helpful in making or excluding the diagnosis?
- What complications can be associated with this parasitic infection, and are there additional treatments that can help to alleviate these complications?
- What is the life cycle of the parasite, and how does the life cycle explain infection in humans?
- How does this organism cause disease?