"Cutaneous larva migrans basically means there is a larva, or the immature form of a hookworm, migrating around under the skin," Bobbi S. Pritt, parasitologist at the Mayo Clinic, tells BuzzFeed News. The microscopic larvae live in sand or soil that has been contaminated with dog or cat feces, says Pritt, and enter the foot by directly penetrating the skin. "The hookworm eggs come out of the stool and hatch in the sand or soil, where they live until an unsuspecting human walks on them barefoot," Pritt says.
This particular skin infection is caused by animal hookworms, as opposed to human hookworms. "Human hookworms are different; they will penetrate the skin but move to the blood and intestinal tract where they cause disease — those don't sit in the skin like the dog and cat ones do," she says.
The worms need a warm, moist environment to survive, so they love tropical areas. "You'll find hookworms in parts of the South in the US but they are endemic to many countries in the Caribbean, as well as Central and South America," Pritt says. The hookworms are common in beaches or rural areas where stray dogs are defecating, since the eggs come from infected feces. But even a glamorous beach resort can have hookworms, too. "Unless you know a beach doesn't allow dogs, you can't be sure," Pritt says.