Raccoon feces could carry eggs from the parasitic roundworm. (Phil Coale/Associated Press)

Parents should be on alert for raccoon roundworm, a rare parasite transmitted through contact with the animal's feces, which has left an infant with brain damage and a teenager blind, says New York City's health department.

Raccoon roundworm or Baylisascaris procyonis is an extremely rare parasitic infection in humans that can cause nausea, nerve damage and even death.

People become infected by swallowing the parasite's eggs that are shed in the feces of infected raccoons.

Parents should supervise children to keep them away from raccoon feces, Sally Slavinski, a spokeswoman for the city's health department, said Monday.

Any droppings should be picked up using gloves and disposed of in trash bags.

There are fewer than 30 cases reported in the medical literature, the city noted in a health alert it sent to the city's doctors on April 9.

Roundworms lay eggs in feces that hatch after being invested and travel through the body, including to the brain.

The infant has been hospitalized since suffering seizures and spinal problems last October and now has permanent brain damage.

The infant had a history of eating soil, and swallowing soil contaminated with raccoon feces is the most likely source of infection, the city's alert said. The 17-year-old lost sight in the right eye in January. Both are from Brooklyn.

"Avoiding Baylisascaris means avoiding ingestion of raccoon stool," veterinarian Scott Weese of the University of Guelph wrote in his blog, Worms & Germs, which promotes safe pet ownership.

"Sounds simple enough, but this is of particular concern with young children and people with developmental delays who are more likely to swallow contaminated dirt or stool, or put dirty/contaminated hands or objects in their mouths."

The city's alert did not include any details about how the teen was exposed.

In September 2005, Toronto Public Health issued a similar alert after a seven-year-old boy with a history of autism and developmental delays was infected with raccoon roundworm.

With files from The Associated Press