A year and a half after traveling abroad, one might think he's free and clear of infection.
But a 25-year-old man in California headed to the emergency room last year with a burning feeling and something squiggling under the white of his eye.
Doctors at the Highland General Hospital Department in Oakland, Calif., immediately started investigating what creature had decided to make its home under the man's skin. They reported on their discovery in the June issue of the Annals of Emergency Medicine and kept his identity anonymous.
Doctors learned he recently returned from a trip to Central and South America. But they realized it was a trip he made to Equatorial Guinea in Central Africa two years earlier on which he got the infection.
For the previous 18 months, the Loa loa worm or Loaiasis (African eye worm) had been crawling underneath his skin causing itchy lesions in its wake, Dr. Shannon Moffett and Dr. Charlotte Page Wills reported in the journal article.
The man couldn't tell what was causing the itchy blotches until it crawled under the layers of skin in his eyeball.
"It moves at a centimeter an hour. It keeps just migrating through the skin," said Dr. David Freedman, director of the University of Alabama at Birmingham Traveler's Health Clinic.
Freedman explained the Loa loa worm infects only humans, but it relies on flies to jump from host to host. A chrysops fly may bite one person who is infected with Loa loa, pick up the larvae from the bite and then transfer them to the next person it bites.
The larvae grow into worms, procreate and lay more larvae that travel in the person's blood stream.
"It will take a period of six months or more for the larvae to become full size and move around," said Freedman. "Once these worms become adults they live for five or 10 years."
Depending on how severe the Loa loa infestation is, doctors can treat it with a drug called diethylcarbamazine. The drug "is available only from the Centers for Disease Control and Prevention, which released it for 10 cases in 2007," the authors wrote.
"I wouldn't say that this is a rare occurrence," said Freedman, speaking of the tropical diseases brought into the United States. "The population with this is mostly returning Peace Corps volunteers."
While there may be only a few cases like this in the U.S., infectious disease experts say that doesn't mean the United States is free from serious parasites -- some which even may cause blindness.
"There are high rates of parasitic infection in the U.S., especially among African American and Hispanic Americans living in poverty," said Dr. Peter Hotez, editor-in-chief of PLoS Neglected Tropical Diseases.
Take, for example, toxocariasis -- a parasite that's passed from dog or cat feces, which Hotez said is often picked up on unclean sidewalks or in playgrounds in the city or country.
"It's a parasitic worm infection that I estimate occurs among 3 million African Americans living in poverty," said Hotez. "It's carried by dogs, and it's associated with asthma and developmental delays."
Hotez said it's possible that a child infected with Toxocara might live their whole life getting asthma treatments, but not be diagnosed with the parasite that actually caused symptoms in the first place.
Each year, more than 700 people infected with Toxocara experience permanent vision loss, according to the CDC.