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Roundworms Carried by Pets Can Cause Blindness

Ƶ MedicalToday

Ocular toxocariasis, though rare, causes blindness in seven out of 10 of those affected by it, typically children, according to a national survey conducted by the CDC.

The agency identified 68 cases during a one-year period, and of the 30 for whom clinical data were available, vision loss occurred in 25 patients (83%) and was permanent in 17 (68%), the agency reported in the June 10 issue of Morbidity and Mortality Weekly Report.

Toxocariasis can occur following the ingestion of embryonated eggs of Toxocara canis and Toxocara cati -- the roundworms that occur in dogs and cats.

Action Points

  • Ocular toxocariasis is caused by the ingestion of embryonated eggs of roundworms excreted in the feces of dogs and cats.
  • Although rare, it most often affects young children and can cause serious ophthalmologic disease, including blindness.
  • Point out that the editorial writers encourage pet owners to immediately dispose of dog and cat feces and to have their pets regularly tested for parasitic infections and dewormed.

These eggs can be found in the feces of infected animals, and are unembryonated when first shed.

The eggs become viable embryos after about two to four weeks in the environment -- usually in dirt or sand. If ingested at this point, the larvae can spread through the body and cause systemic reactions. Migration to the eye causes ocular toxocariasis.

In an editorial note, the agency emphasized that most cases of Toxocara infection result from ingestion of soil, such as in playgrounds and sandboxes, that has been contaminated by dog or cat feces.

Among the 68 cases identified in the CDC report, which was based on surveys sent to more than 3,000 ophthalmologists, demographic information was available for 44.

Patients' median age was 8½, slightly more than half were male, and the majority were white.

A total of 57% lived in the South, with the highest numbers of cases being reported in Georgia, Florida, California, and Texas.

That's probably a function of climate, the report noted: The larvae don't mature in temperatures below 50° F, so maturation is more likely in areas where the soil is warmer.

Besides loss of vision, other symptoms include photophobia, redness of the eyes, and the presence of floaters.

Other frequent ocular signs included:

  • Subretinal granulomatous mass or scar, 65%
  • Vitritis, 55%
  • Scotoma, 50%
  • Posterior pole granuloma, 42%
  • Peripheral granuloma with traction bands, 39%

Seven patients underwent scleral buckling and pars plana vitrectomy with the goal of improving their vision, and 11 were treated with corticosteroids.

The editorial writers recommended that efforts to prevent Toxocara infection and its potentially devastating visual consequences be based on an approach established by the One Health initiative, which is intended to promote the health of humans, animals, and the environment.

Such an approach requires healthcare providers to be familiar with the signs and symptoms of toxocariasis, and to inform their patients about the potential hazards of exposure to contaminated soil and pet feces.

Sanitary measures also should be encouraged, such as frequent handwashing and prompt disposal of animal feces.

In addition, veterinarians should advise pet owners of the need for routine testing for parasites and deworming of all infected animals.

Disclosures

Several authors are employees of the CDC.

Primary Source

Morbidity and Mortality Weekly Report

Centers for Disease Control and Prevention "Ocular toxocariasis -- United States, 2009-2010" MMWR 2011; 60: 729-733.