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A-Z Glossary

Table of Contents

Toxocariasis

Courtney Dryer, OD
Written byCourtney Dryer, OD
Courtney Dryer, OD
Courtney Dryer, ODOptometristCharlotte, NC

Bio

Dr. Courtney Dryer earned her doctorate from Southern College of Optometry, Memphis, Tennessee in 2011. She opened her own practice Autarchic Spec Shop in 2013 in Charlotte, NC. She has had the privilege of writing for numerous optometric publications and serving in various industry capacities. In 2015, Vision Monday named her a rising star and one of the most influential women in optometry. Her optometric passions include practice management, specialty contact lenses, and dry eye management.

  • Last updated March 22, 2023

What is Toxocariasis?

Ocular Toxocariasis is a rare infection from common roundworms Toxocara canis and Toxocara cati. It typically affects children and can lead to a significant loss of vision despite medical and surgical therapies. Toxocara canis and Toxocara cati are among the most widely distributed helminthic species in the world with a high zoonotic impact. Millions of people have been infected and hundreds of thousands are suffering from toxocariasis. 

The disease has two major categorizations: visceral larva migrans (VLM) and ocular larva migrans (OLM). Toxocara antibody levels in the United States are estimated at 13.9%, but symptomatic infections are significantly less common, especially OLM.

Key Takeaways

  • Ocular Toxocariasis is an infection caused by roundworms that results in unilateral vision loss.
  • The roundworms live in dog and cat intestines and contact leads to infection.
  • Proper hygiene and public awareness are key to prevention.
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Understanding Toxocariasis

Toxocariasis can be found worldwide. The nematodes live and mature in dog or cat intestines. As a mature adult, the organism releases eggs which are passed in the stool. Human contact with infected materials leads to human infection. The clinical course in humans varies from asymptomatic infection to severe organ injury and depends on the parasite load, the sites of larval migration, and the host’s inflammatory response.

The clinical presentation can be classified into one of four forms:

  1. Posterior pole granuloma
  2. Peripheral granuloma
  3. Nematode endophthalmitis
  4. Atypical presentation

Risk Factors for Toxocariasis

Geophagia (deliberate consumption of earth, soil, or clay) at a young age, playing in sandboxes, and exposure to and ownership of puppies and kittens are risk factors for Toxocariasis.  In puppies 2 to 6 months old, the prevalence of Toxocara Canis has been reported to be over 80%; however, in dogs older than one year this number drops to 20%. Water or food contaminated with the Toxocara eggs is another possible exposure.

Toxocariasis Symptoms

The symptoms of toxocariasis usually present unilaterally and include:

  • Reduced vision
  • Photophobia
  • Floaters
  • Leukocoria (white pupil)
  • Pain

Diagnosing Toxocariasis

An eye doctor will take a comprehensive history and perform a dilated eye exam. In the back of one eye, they may view vitritis which is common in 90% of patients. If the infection is acute, Toxocara retinochoroiditis appears as a hazy, ill-defined white lesion with overlying vitritis. As it resolves, the lesion becomes a more distinct, demarcated, elevated white mass ranging from one-half to four-disc diameters in size. Atypical presentations may include inflammation and swelling of the optic nerve head, motile subretinal larvae, and diffuse chorioretinitis. Conjunctivitis, keratitis, iridocyclitis, focal iris nodules, and cataracts can also be observed. 

Toxocariasis Treatment

Management includes quieting the inflammation, eliminating the offending organism, and repairing vitreoretinal findings.  Blood work like an ELISA may be useful for ocular toxocariasis. Several imaging modalities are now used to visualize the manifestations of larvae and assist in the diagnosis and management of this infection.  

Medical therapy includes topical steroids to limit inflammation and prevent the development of tractional membranes and retinal detachments. Other options include periocular injections and oral corticosteroids at 0.5-1 mg/kg. In the case of anterior segment inflammation, cycloplegics are also used to prevent the formation of synechiae. The use of anti-parasitic therapy is unproven in the case of ocular toxocariasis. There is some support for the use of albendazole or thiabendazole to eradicate the organism. 

The CDC reports that approximately 25% of new cases of ocular toxocariasis require surgery. Vitrectomy is the most common surgery performed for ocular toxocariasis. Individuals may need surgery for persistent vitreous opacification, hemorrhage, tractional retinal detachment, and epiretinal membranes. 

Prevention of Toxocariasis

For the most part, the public is unaware of Toxocariasis. Increasing public awareness and reducing human exposure is the key to prevention. As the disease is more common in children, it’s important that they practice good hygiene, like handwashing after exposure to sandboxes, parks, and playgrounds. In adults, ingestion is most common, and an association has been found with eating raw meat especially raw cow liver.

Bibliography

  1. Ahn SJ, Ryoo NK, Woo SJ. Ocular toxocariasis: clinical features, diagnosis, treatment, and prevention. Asia Pac Allergy. 2014;4(3):134-141. doi:10.5415/apallergy.2014.4.3.134
  2. Auer, H, Walochnik, J.Chapter Six – Toxocariasis and the clinical spectrum, Editor(s): Dwight D. Bowman, Advances in Parasitology, Academic Press, Volume 109, 2020, Pages 111-130, ISSN 0065-308X, ISBN 9780128209585, https://doi.org/10.1016/bs.apar.2020.01.005.
  3. Dietrich CF, Cretu C, Dong Y. Imaging of toxocariasis. Adv Parasitol. 2020;109:165-187. doi: 10.1016/bs.apar.2020.03.001. Epub 2020 Apr 25. PMID: 32381196.
  4. Toxocariasis. AOA Wiki Eye. Retrieved October 22, 2022, from https://eyewiki.org/Toxocariasis

 

Related Terms

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Deuteranopia

is a type of red-green color deficiency. Those with deuteranopia see things with more red color

Uvea

is a highly vascular layer that lines the sclera, and its primary function is to provide nutrition to the eye

Retrobulbar Hemorrhage

is a condition in which blood accumulates in the orbital cavity, the space behind the eyeball

Blepharochalasis

Occurs when the eyelids suddenly become inflamed and swell

Achromatopsia

is a retinal condition that results in the inability to see color

Blepharoconjunctivitis

is an eye condition that combines blepharitis and conjunctivitis

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