Dog parasite worms its way into humans.

Gardeners and barefoot strollers may be inviting a common canine hookworm to take up residence in their intestines -- unless they take precautions, researchers warn.

John Croese of the University of Queensland in Australia and his colleagues recently diagnosed nine cases of human infection with the hookworm Ancylostorna caninum. The worm normally resides in man's best friend but appears to threaten people as well, the researchers report in the March 1 ANNALS OF INTERNAL MEDICINE.

The patients, all dog owners, probably became infected when they touched soil or grass contaminated with dog feces, the researchers report.

Since the 1920s, physicians have sporadically reported cases of human infection with A. caninum. However, until 1991, no one had linked the worm to an intestinal disease.

A. caninum "is a cosmopolitan species, exceedingly common in both tropical and temperate areas, including North America," Gerhard A. Schad of the University of Pennsylvania School of Veterinary Medicine in Philadelphia writes in an editorial accompanying the report. A number of different drugs can be used to rid dogs of the worms, he adds.

Croese and his coworkers removed the worms from patients during a colonoscopy or other medical procedure. "After removal of the worm, all patients recovered and have remained well" they report.

People infected with A. caninure may have no noticeable symptoms. The patients in this study, however, all had diarrhea, abdominal pain and distension, weight loss, rectal bleeding, and elevated IgE, an immunoglobulin, they report.

Diagnosis of this hookworm infection proved difficult. Because A. caninum does not lay eggs in humans, stool samples contain no telltale ova, explains Schad. Sometimes, only one small, elusive worm sets up house in the intestine. Croese and his colleagues identified the worms under the microscope or by testing patients for the antibody to the parasite, they write.