Toxocara Canis (Visceral Larva Migrans, Toxocariasis)


Article Author:
Walter Winders


Article Editor:
Lacey Menkin-Smith


Editors In Chief:
Silvio de Melo Jr.
Vittorio Giuliano
Truptesh Kothari


Managing Editors:
Avais Raja
Orawan Chaigasame
Carrie Smith
Abdul Waheed
Khalid Alsayouri
Trevor Nezwek
Radia Jamil
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Steve Bhimji
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beata Beatty
Nazia Sadiq
Hajira Basit
Phillip Hynes
Tehmina Warsi


Updated:
2/27/2019 9:00:18 PM

Introduction

Human toxocariasis is a helminthic infection that primarily impacts populations of lower socioeconomic class in tropical and subtropical latitudes around the world.  It is a roundworm (also known as nematode) that is not frequently clinically consequential; however, it is known to have severe complications such as blindness or meningoencephalitis. 

Two main species of Toxocara affect humans: Toxocara canis and Toxocara cati.  Definite hosts include cats, dogs, foxes, coyotes, and wolves.  These hosts harbor the nematodes in their gut, shedding eggs in their feces.  These embryonated eggs remain infectious for years outside the definitive host.  In the wild, intermediate hosts such as other cats, dogs, rabbits, and fowl ingest the cysts, which hatch and migrate to various muscles and organs to encyst.  In the wild, carnivorous animals such as cats and dogs consume infected meat (or simply soil containing the eggs), and the parasite remains in their gut.  Additionally, there is solid documentation of transplacental transmission in dogs and cats.  Humans are amongst a plethora of possible intermediate animal hosts.  Clinical disease results from the migration of the parasite through extra-intestinal tissues.[1][2] 

Etiology

Clinical Toxocariasis is a product of Toxocara species migration through tissues.  Toxocara canis primarily infects canids (dogs, foxes, and wolves) whereas T. cati primarily infects felids (cats).  T. cati is thought to more frequently cause severe human disease. Children are more prone to infection via the fecal-oral route as they are more likely to consume Toxocara eggs by ingesting soil or other contaminated substances.  Epidemiologic studies have found that public parks with community sandboxes have particularly high egg burdens, placing children frequenting these areas at risk.[3]

Epidemiology

Toxocara species are prevalent worldwide — their concentration is in areas with large populations of domestic dogs and cats. Worldwide, Toxocara predominantly affects children in tropical and subtropical regions.  Globally, the disease is more common in developing countries, with seroprevalence reported above 80% in children in parts of Nigeria.[4] In the United States, the seroprevalence estimates range from 5% to 15% and approximately 10000 clinical cases are diagnosed yearly.[5][6] Risk factors for disease contraction include poverty, latitude, contaminated soil, young age, and high concentration of dogs and cats.  There is a large discrepancy in prevalence between the developed and developing world just due to these risk factors. 

Pathophysiology

Clinical disease is due to parasitic nematode larva migration through tissues.  The signs and symptoms differ based on the affected organ and the host inflammatory response.  There are four types of disease: ocular larva migrans (OLM), visceral larva migrans (VLM), neurotoxocariasis, and covert toxocariasis. The covert disease most often presents with simple, persistent eosinophilia and may be attributed to the continuation of the migratory phase.  Interestingly, this migratory phase may last for years.[7]

History and Physical

Ocular larva migrans (OLM) is caused by larval migration through the posterior segment of the eye and is a leading infectious cause of blindness in children in developed countries.  OLM classically presents with unilateral vision loss in a child, most often between the ages of five to ten.  The exam may demonstrate uveitis, retinitis, choroiditis, or endophthalmitis based on the location of the parasite.  The infection can also result in secondary glaucoma. Histologically, eosinophilic abscesses with surrounding granulomatous reactions are the expected manifestations.

Visceral larva migrans (VLM) is caused by larval migration through both solid and hollow organs in the abdomen and should be considered in any child presenting with fever, nausea, vomiting, abdominal pain and eosinophilia. An exam may be notable for hepatosplenomegaly, which can serve as a clue for clinicians that the presentation is not simple viral gastroenteritis.  Lung involvement can result in bronchospasm and wheezing.

Central nervous system disease is rare but can be severe and range from eosinophilic meningitis to fulminant meningoencephalitis, presenting with seizures, encephalopathy or neuropsychiatric symptoms.[7][8]

Evaluation

Diagnosis of toxocariasis is difficult. While identification of the organism on microscopy is the gold standard, it is rarely achieved for practical reasons.  ELISA assays are available and recommended; yet, they, unfortunately, have relatively poor sensitivity (approximately 80%).[9] Additionally, given that humans are not definitive hosts for Toxocara, stool microscopy is ineffective.  Other secondary indicators of infection include eosinophilia and hypergammaglobulinemia.  However, these markers are not specific, and their sensitivities do not have extensive backing in the literature. Clinical diagnosis and presumptive treatment is an option to consider in the right clinical context.

Treatment / Management

For the treatment of VLM, albendazole and mebendazole both are effective. Albendazole is recommended as it has superior tissue penetration than mebendazole.  The dose of albendazole is 10 mg/kg/day divided into two doses for five days.  Depending on other endemic infections, ivermectin and DEC (diethylcarbamazine) may be useful as well.  Treatment of OLM is more difficult and revolves around decreasing inflammation.  Thus, prednisone is often an addition to antihelminthic agents and surgery is reserved for only the most severe cases.[7][9]

Differential Diagnosis

The differential diagnosis for VLM is broad as many infections may cause eosinophilia and fever.  As this is a global disease, local epidemiology is paramount.  Considerations include ascariasis (Löffler’s syndrome), trichinosis, strongyloides, onchocerciasis, schistosomiasis, paragonimus, entamoeba histolytica, and Fasciola hepatica. 

The central differential for OLM is retinoblastoma.  The disease was originally discovered in the 1950s in enucleated eyes suspected to have retinoblastoma.

Eosinophilic meningitis has a narrow differential diagnosis as well: angiostrongylus (rat-lung worm) is the chief consideration.

Prognosis

The prognosis for VLM is generally good; however, chronic disease has potential correlations with both epilepsy and cognitive delay. 

Complications

Per above, complications, while rare, include blindness, severe neurologic disease, and even death.

Deterrence and Patient Education

Given that toxocariasis spreads via the fecal-oral route, patient education in hand-hygiene is vital in risk factor modification. Also, patients should receive instruction on other risk factors such as exposure to pets and places where animal feces are present such as sandboxes. Common pitfalls amongst healthcare providers include failure to consider this diagnosis in children.  The true disease burden is likely underestimated, and while failure to diagnose VLM may not carry acute complications, the chronic and economic burden of disease is likely profound.[3]

Enhancing Healthcare Team Outcomes

The management of Toxocara is complicated as it is more than human disease and requires a One Health approach.  Domestic animal carrier rates directly impact the risk of acquisition, vertical transmission is common in dogs and cats, and no vaccine exists.  Thus, interprofessional collaboration is necessary for adequate control.   The first challenge is increasing awareness.  Toxocara is considered a neglected tropical infection, given the minimal level of research, funding, and publicity it receives in spite of carrying a significant burden of disease. The role of the primary caregiver and nurse practitioner is invaluable in educating patients on preventing this parasitic infection.


Interested in Participating?

We are looking for contributors to author, edit, and peer review our vast library of review articles and multiple choice questions. In as little as 2-3 hours you can make a significant contribution to your specialty. In return for a small amount of your time, you will receive free access to all content and you will be published as an author or editor in eBooks, apps, online CME/CE activities, and an online Learning Management System for students, teachers, and program directors that allows access to review materials in over 500 specialties.

Improve Content - Become an Author or Editor

This is an academic project designed to provide inexpensive peer-reviewed Apps, eBooks, and very soon an online CME/CE system to help students identify weaknesses and improve knowledge. We would like you to consider being an author or editor. Please click here to learn more. Thank you for you for your interest, the StatPearls Publishing Editorial Team.

Toxocara Canis (Visceral Larva Migrans, Toxocariasis) - Questions

Take a quiz of the questions on this article.

Take Quiz
A 5-year-old female presents with abdominal pain and splenomegaly. Based on risk factors, parasitic infection is suspected. Which of the following tests is used to make the diagnosis of visceral larva migrans?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 4-year-old boy presents with monocular vision loss. Symptoms started less than 24 hours ago and have been progressive. There has been mild pain, and the eye is fairly injected on exam. No hyphemia or hypopyon is noted. On further questioning, the family has several dogs at home, and the younger sister recent took medicines for an abdominal infection. Infectious process is suspected. What is the likely organism?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A child presents with fever, eosinophilia, abdominal pain, and mild splenomegaly noted on exam. It is suspected this is more than the gastroenteritis. The parents report there are multiple dogs and cats at home. What is the drug of choice?



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up
A 4-year-old female from the United States complains of problems breathing. She likes to eat dirt. She has no past medical history, travel history, or sick contacts. The patient has bilateral wheezing and hepatomegaly. The family has a dog. CBC shows leukocytosis with 55 percent eosinophilia. Select the best diagnostic test.



Click Your Answer Below


Would you like to access teaching points and more information on this topic?

Improve Content - Become an Author or Editor and get free access to the entire database, free eBooks, as well as free CME/CE as it becomes available. If interested, please click on "Sign Up" to register.

Purchase- Want immediate access to questions, answers, and teaching points? They can be purchased above at Apps and eBooks.


Sign Up

Toxocara Canis (Visceral Larva Migrans, Toxocariasis) - References

References

Ain Tiewsoh JB,Khurana S,Mewara A,Sehgal R,Singh A, Clinical and laboratory characteristics of patients with toxocariasis encountered at a tertiary care centre in North India. Indian journal of medical microbiology. 2018 Jul-Sep;     [PubMed]
Chen J,Liu Q,Liu GH,Zheng WB,Hong SJ,Sugiyama H,Zhu XQ,Elsheikha HM, Toxocariasis: a silent threat with a progressive public health impact. Infectious diseases of poverty. 2018 Jun 13;     [PubMed]
Fakhri Y,Gasser RB,Rostami A,Fan CK,Ghasemi SM,Javanian M,Bayani M,Armoon B,Moradi B, Toxocara eggs in public places worldwide - A systematic review and meta-analysis. Environmental pollution (Barking, Essex : 1987). 2018 Nov;     [PubMed]
Sowemimo OA,Lee YL,Asaolu SO,Chuang TW,Akinwale OP,Badejoko BO,Gyang VP,Nwafor T,Henry E,Fan CK, Seroepidemiological study and associated risk factors of Toxocara canis infection among preschool children in Osun State, Nigeria. Acta tropica. 2017 Sep;     [PubMed]
Berrett AN,Erickson LD,Gale SD,Stone A,Brown BL,Hedges DW, {i}Toxocara{/i} Seroprevalence and Associated Risk Factors in the United States. The American journal of tropical medicine and hygiene. 2017 Dec;     [PubMed]
Farmer A,Beltran T,Choi YS, Prevalence of Toxocara species infection in the U.S.: Results from the National Health and Nutrition Examination Survey, 2011-2014. PLoS neglected tropical diseases. 2017 Jul;     [PubMed]
Woodhall DM,Fiore AE, Toxocariasis: A Review for Pediatricians. Journal of the Pediatric Infectious Diseases Society. 2014 Jun;     [PubMed]
Lee RM,Moore LB,Bottazzi ME,Hotez PJ, Toxocariasis in North America: a systematic review. PLoS neglected tropical diseases. 2014 Aug;     [PubMed]
Iddawela RD,Rajapakse RP,Perera NA,Agatsuma T, Characterization of a Toxocara canis species-specific excretory-secretory antigen (TcES-57) and development of a double sandwich ELISA for diagnosis of visceral larva migrans. The Korean journal of parasitology. 2007 Mar;     [PubMed]

Disclaimer

The intent of StatPearls is to provide practice questions and explanations to assist you in identifying and resolving knowledge deficits. These questions and explanations are not intended to be a source of the knowledge base of all of medicine, nor is it intended to be a board or certification review of Gastroenterology. The authors or editors do not warrant the information is complete or accurate. The reader is encouraged to verify each answer and explanation in several references. All drug indications and dosages should be verified before administration.

StatPearls offers the most comprehensive database of free multiple-choice questions with explanations and short review chapters ever developed. This system helps physicians, medical students, dentists, nurses, pharmacists, and allied health professionals identify education deficits and learn new concepts. StatPearls is not a board or certification review system for Gastroenterology, it is a learning system that you can use to help improve your knowledge base of medicine for life-long learning. StatPearls will help you identify your weaknesses so that when you are ready to study for a board or certification exam in Gastroenterology, you will already be prepared.

Our content is updated continuously through a multi-step peer review process that will help you be prepared and review for a thorough knowledge of Gastroenterology. When it is time for the Gastroenterology board and certification exam, you will already be ready. Besides online study quizzes, we also publish our peer-reviewed content in eBooks and mobile Apps. We also offer inexpensive CME/CE, so our content can be used to attain education credits while you study Gastroenterology.