Ocular Toxocariasis — United States, 2009–2010

Flora C. Lum, MD; H. Dunbar Hoskins Jr, MD; Ramana S. Moorthy, MD; Russell W. Read, MD; Michelle C. Starr; Susan P. Montgomery, DVM; Jeffrey L. Jones, MD; Dana M. Woodhall, MD


Morbidity and Mortality Weekly Report. 2011;60(22):734-736. 

In This Article

Editorial Note

Dogs and cats are the respective definitive hosts for the zoonotic parasites T. canis and T. cati. Infected dogs or cats pass unembryonated eggs in their feces; after 2 to 4 weeks in the environment, the eggs embryonate and become infectious. If embryonated eggs are consumed unintentionally by humans, the Toxocara larvae emerge and are able to migrate throughout the body, causing severe systemic reactions. Toxocara infection in humans occurs most commonly through ingestion of contaminated soil. Toxocara is found in all regions of the United States; however, development of Toxocara larvae does not occur below 50ºF (10ºC), making soil in warmer climates more conducive to contamination with infectious Toxocara eggs.[5]

Children are especially at risk for infection from exposure to playgrounds and sandboxes contaminated by dog or cat feces.[6–7] Several case studies have documented a clinical ocular manifestation with severe vision impairment in children.[1–4] Previous studies of OT in the United States have been conducted within single institutions, with only one multicenter survey performed in 1987 in Alabama, which indicated an estimated statewide prevalence of one per 1,000 persons.[8] Testing data for a representative sample of the U.S. population aged ≥6 years from the Third National Health and Nutrition Examination Survey (NHANES III) demonstrated an overall prevalence of 13.9% positive for antibodies to Toxocara; however, serologic testing does not reliably indicate active infection, nor does a negative test result rule out Toxocara infection.[9]

Treatment of OT is aimed at reducing inflammation through the use of corticosteroids and antihelminthics; various ophthalmologic surgical procedures may be used to minimize complications from severe disease. However, data are limited regarding optimal treatment strategies, and irreversible ocular damage has already occurred in most OT patients by the time they are examined by an ophthalmologist. The survey described in this report was conducted in an effort to better understand the impact of toxocariasis in the United States by collecting information on OT, which is readily diagnosed by clinical presentation.

The findings in this report are subject to at least three limitations. First, the response rate (19%) of survey respondents was low, which likely is attributable to the significant amount of time required to access and abstract the patients' medical records for the requested data and to complete the survey. Ophthalmologists who did not have OT patients likely elected not to participate in the survey, which also might have contributed to the low response rate. Second, the results might be subject to responder bias because the surveyed ophthalmologic subspecialists might be more likely to report more severe disease, which might contribute to the underrepresentation of patients with mild OT clinical manifestations. Finally, the findings might be subject to selection bias because persons with limited access to health care might not have access to subspecialty ophthalmologic care. All three limitations likely would contribute to underreporting of OT patients.

Prevention of toxocariasis requires a One Health approach,* incorporating the collaboration of groups invested in protecting the health of humans, animals, and the environment. Good hygiene practices, such as hand washing, should be encouraged especially after contact with pets or areas at high risk for soil contamination, such as playgrounds and sandboxes. Health-care providers should be aware of clinical manifestations of toxocariasis and educate their patients at risk, especially children, about avoiding exposure to potentially contaminated soil and preventing infection in their pets. Veterinarians should encourage pet owners to immediately dispose of dog and cat feces and to have their pets regularly tested for parasitic infections and dewormed. Controlling Toxocara infection in dogs and cats and preventing exposure of persons to possible sources of infection will prevent infection and decrease morbidity associated with Toxocara. Additional information about toxocariasis is available at https://www.cdc.gov/parasites/toxocariasis.

* The One Health initiative seeks to improve the health of all humans and animals through the integration of human medicine, veterinary medicine, and environmental science. Additional information available at https://www.onehealthinitiative.com.


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