The Centers for Disease Control (CDC) reports that the frequency of worms transmitted from dogs and cats to humans is higher than previously believed, according to the results of a new study released Nov. 5, 2007.

The study revealed that the transmission of Toxocara (internal roundworms) from dogs and cats to humans is more prevalent in those ages 20 and younger. Children are more susceptible due to increased activity outdoors as well as their propensity to play in and ingest contaminated soil, according to the CDC.

The illness is passed from infected animals to humans who ingest the Toxocara eggs found in the animals’ feces. Transmission may occur in areas contaminated with dog and cat feces – including sandboxes and children’s play areas, according to the CDC.

In addition, the study showed that Toxocara is more prevalent in non-Hispanic blacks than Mexican-Americans and non-Hispanic whites across all age groups.

Approximately 14 percent of the U.S. population is infected with Toxocara, CDC officials stated.

“The results of this study demonstrate that Toxocara infection in the United States is more widespread and common that previously understood,” said Peter Schantz, an epidemiologist in the Division of Parasitic Diseases at the CDC. “Although most persons infected with Toxocara have no apparent symptoms, this infectious agent is capable of causing blindness and other serious systemic illnesses, which makes it a public health issue.”

Although it’s rare, blindness most often affects children, Schantz said. However, the exact number of Toxocara cases resulting in visual impairments is not known because the illness is not a reportable infection.

To decrease human infections, pet owners should treat their dogs and cats with year-round parasite prevention and control in order to reduce the number of infected pets transmitting the illness, according to the Companion Animal Parasite Council, a nonprofit organization.