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.
1) The Loa Loa Worm
"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.
Hotez said two other infections -- toxoplasmosis and congenital cytomegalovirus (CMV) which can cause deafness and psychomotor retardation -- infect people in the United States.
In May 2010, Rep. Hank Johnson, D-Ga., introduced a bill to Congress that would push the Health and Human Services department to investigate and address these parasites in the U.S.
"If these infections were occurring among wealthy people in the suburbs, we would not tolerate it," said Hotez, of the Department of Microbiology, Immunology and Tropical Medicine at the George Washington University and Sabin Vaccine Institute in Washington, D.C.
Indeed some of the more noticeable reports about parasites come from travelers abroad, who often are shocked and disgusted by their infections.
Below is a list of some of the more common parasites to avoid at home and around the world, along with some expert advice on how to rid yourself of the worms.
2) The Human Bot Fly
Tara Dairman, 30, was confused by a painful itching on her scalp this December after returning from months abroad in Central and South America.
"I thought the bite was really weird when we got home because we were in Indiana and it was cold," said Dairman.
Dairman quickly found she had been infested with not one, but two painful parasites in her scalp. Her run-in with a blood-sucking bug happened in the jungle of Belize, but there are plenty of parasites one can catch in the United States. "We're pretty sure that they came from the jungle in Belize," Dairman said of the two bot fly larva that embedded themselves in her scalp.
Dairman and her husband, Andrew Cahill, 30, already had plenty of bot fly (Dermatobia hominis) bites from the trip. But little did the couple know the bot fly lays its eggs in a more insidious way.
"They actually capture a mosquito or a tick and they lay their eggs on their stomachs," said Dairman. The bot fly then releases the mosquito or tick and hopes it will find a good host -- like Dairman -- to bite.
The warmth of the blood the mosquito sucks from the body prompt the bot-fly eggs to hatch. The larvae then embed themselves in the skin either through the new insect bite or a hair follicle, according to the University of Florida Institute of Food and Agricultural Sciences.
As if that's not bad enough, the larvae start to grow spikes on its body to keep hosts like Tara from pulling them out as they feed on her flesh.
"They have these little barbs in them so either when they move or when they're feeding it feels like this hot needle stabbing into you," said Dairman.
Days after the first symptoms, Dairman discovered she had a second itchy, painful spot on her head that caused a lot of pain.
But Cahill couldn't see what Dairman was talking about. With some Internet searches the couple matched Dairman's symptoms to the notorious bot fly. They also read the best way to find the larvae is to try and deprive them of oxygen.
Put on some form of grease, in this case Vaseline, and the larvae will burrow upwards and fight for air.
The couple would have visited a dermatologist, but wanted to see if they could do it without paying hundreds of dollars for a visit.
"Since we quit our jobs to go traveling we don't have health insurance to cover us in the United States, we only have insurance for emergencies," said Dairman.
If you're fast enough you can grab them with tweezers and (painfully) pull them out. Cahill however, found it was better to suffocate them first.
"We covered them with New-Skin for the night to cut off their air supply," Cahill wrote on their blog, "Andy and Tara's World." "New-Skin is basically fingernail polish that is meant to go on small cuts and scrapes for protection. This morning when we got up, we peeled the New-Skin off one of them and the dead worm was visible."
Dairman said she'd go back to Belize, even after her experience with the bot fly.
"Belize is terrific. So I'd certainly recommend it to anyone," said Dairman. "I think this is really rare."
3) Fish Tapeworms
For a spare few aficionados of raw fish, the delicacy they love can lead to a very unwelcome visitor -- the kind that takes up residence in your intestines.
Anthony Franz was one such case. In the summer of 2006, he went to a Chicago area hospital carrying a 9-foot tapeworm that had come from his digestive tract.
Franz, who was not available for comment, filed a lawsuit against an Illinois seafood restaurant for $100,000 last spring.
"Basically we discovered that this particular tapeworm was caused from uncooked seafood, particularly salmon," said Franz's attorney, Gregory Leiter. "That's what he brought into the hospital."
Franz is one of the small but growing number of tapeworm victims in cities across the world who are discovering (or rediscovering) that some of the most popular fish can host parasites.
Fortunately, the number of people who have a story similar to Franz's is still relatively low; a recent study in the journal Emerging Infectious Diseases pegged the number at just 1 per 100,000 people in Kyoto, Japan in 2008.
But as sashimi and other raw fish dishes grow in popularity, experts say such cases could become more common.
"Usually, with this particular warm it produces discomfort, some pain, and it can produce anemia," Dr. Felipe C. Cabello, professor of Microbiology and Immunology at New York Medical College in Valhalla, told ABCNews.com.
The worm rarely poses an imminent danger to health, Cabello said. But he added that its presence can leave its host drained.
"The parasite sucks the vitamin B12, and the person with the parasite does not have enough," said Cabello. "This is a worm that can reach 25 feet and it might take months, a year to grow."
4) Taenia Solium
For Rosemary Alvarez, it was a diagnosis that brought both relief and revulsion.
The relief came when Alvarez, a 37-year-old Phoenix resident, learned from her surgeon that her neurological symptoms had not been caused by a brain tumor, as her doctors had initially suspected.
But the revulsion soon followed -- when the surgeon said her balance problems, her difficulty swallowing and the numbness in her left arm had been caused by a worm he had just pulled out of her brain.
"She was deteriorating rather quickly, so she needed it out," Dr. Peter Nakaji, a neurosurgeon at the Barrow Neurological Institute at St. Joseph's Hospital and Medical Center, told ABC News.
But when Nakaji cut into Alvarez's brain to extract what he thought was a tumor, he instead found a parasite living in her brain -- a tapeworm called Taenia solium, to be precise.
"I was actually quite pleased," said Nakaji. "As neurosurgeons, we see a lot of bad things and have to deliver a lot of bad news."
Unfortunately, it is difficult to avoid the worm, which usually only infects pigs. Nakaji said Alvarez's hygiene habits were probably not to blame. It was more likely that someone, somewhere, had served her food tainted with the feces of a person infected with the pork tapeworm parasite.
Parasitologists say that while brushes with the pork tapeworms remain relatively rare, they endure in certain areas of the country.
"We've got a lot more of cases of this in the United States now," said Raymond Kuhn, professor of biology and an expert on parasites at Wake Forest University in Winston-Salem, N.C. "Upwards of 20 percent of neurology offices in California have seen it."
And the eggs of the worm are nothing if not resilient.
"These eggs can live for three months in formaldehyde," said Kuhn. "You got to think, sometimes, a person is slapping lettuce on your sandwich with a few extra add-ons there."
5) Lice and Bedbugs
"Don't let the bedbugs bite."
What once might have been a facetious nighttime saying became pretty good advice for New York City commuters in 2008, as an official with the city's Department of Housing, Preservation and Development told an audience that the city's subway trains and stations may have been infested with the insects.
The New York City Transit Authority immediately defended itself. But Edward Brownbear, lead education instructor for the housing department and the city's top bedbug authority, reportedly said that he himself had seen the bugs on the wooden benches of Manhattan's Union Square station and The Bronx's Fordham Road station -- as well as on the clothing of a passenger on a train.
At least one Manhattan pest control professional agreed at the time that bedbug infestation had been a growing problem in the city's subway system.
"I've been talking about it for five years," said Jeffrey Eisenberg, president of Pest Away Exterminating, adding that he had personally reported bedbug sightings to subway administrators seven to eight years before.
Efforts to track the critters have revealed that, after a long decline, bedbugs have rebounded in the United States in recent years. This is partly because of increased international travel. The tiny, nocturnal insects are able to live in both fibers and wood. They are also known for their bites, which cause itchy bumps on the skin.
But the bite can lead to more than an itch. According to reports from the U.S. Public Health Service, bedbugs are known to carry dozens of infectious diseases, from smallpox to the flu.
And where people are, the bugs are sure to follow, said Cindy Mannes, spokeswoman for the National Pest Management Association.
"If you think about large groups of people, in many cases this is how bedbugs are transported," Mannes said at the time. "I know they've been found in movie theaters and other strange places."
6) Guinea Worm
The horrific nature of a Guinea worm infection is perhaps best captured in its Latin name -- Dracunculus medinensis. Roughly translated, the term means "little dragon of the Mediterranean."
Despite its small size, the Guinea worm can cause excruciating pain. The pest infects a human host through contaminated drinking water. The larvae of the worm mature in one's stomach and reproduce in the intestines. The mature female worms migrate to the surface of the skin. There, the worms embed themselves, growing up to three feet in length.
Primarily found in the Middle East and many African countries, the Guinea worm enjoys a colorful history shared by few other parasites. It has been found during the dissection of Egyptian mummies and is well documented in ancient texts. There are even possible references to it in the Old Testament.
Some even believe that the Guinea worm was the inspiration for the design of the caduceus -- the serpent-entwined staff that is now the symbol of the medical profession. The theory springs from the fact that in the ancient world, the proper removal of the worm involved grabbing the exposed tail and gradually winding the body of the worm around a stick -- as pulling too hard would cause the worm to break, resulting in infection and inflammation. Thus, some believe, the symbol of the parasite twisted around a stick became synonymous with the healing arts.
Fortunately, public health efforts appear to have largely turned the tide against Guinea worm infections. According to statistics compiled by The Carter Center http://www.cartercenter.org/health/guinea-worm/index.html -- the disease-fighting nonprofit organization founded by former U.S. President Jimmy Carter -- eradication efforts have reduced the number of cases reported in 20 African nations from 3.5 million in 1986 to just a few thousand last year. And some hope that the disease will be completely eradicated within the next few years.
Arguably the deadliest parasite ever known to man, a microscopic organism known as Plasmodium is responsible for the disease known as malaria. The disease is spread by mosquitoes, and each year between 350 million and 500 million people worldwide fall ill from it, according to statistics from the CDC. Of those stricken, more than a million die.
Those infected with malaria generally have fever, headache, and vomiting, starting 10 to 15 days after contracting the disease from a mosquito bite. The deadliest form of the parasite, called Plasmodium falciparum, can rapidly threaten the lives of its victims by disrupting blood supply to vital organs.
The deadly nature malaria has put it in the crosshairs of global health organizations and charitable institutions alike.
"Malaria still kills more than 1 million people every year," said U.N. Secretary-General Ban Ki Moon during a speech on World Malaria Day in April 2008. "The toll it is taking is unacceptable -- all the more so because malaria is preventable and treatable."
And the solutions for this devastating disease are simple ones. Bednets, insecticides and inexpensive antimalarial drugs all go a long way in the areas where it still threatens humans, primarily in sub-Saharan Africa.
8) Chagas Disease
For many, infection with Chagas disease takes place in the dead of night.
When the lights go out in many of the adobe and mud homes inhabited by the rural poor in Central and South America, the triatomine beetle -- also known as the "kissing bug" -- creeps out from the crevices in walls and ceilings, seeking out warm, sleeping bodies.
The bug got its seemingly-romantic nickname because it is attracted to its victims' faces. At night one's face is generally uncovered and gives off body heat. The insect sucks one's blood through a long proboscis. As it feeds, it defecates -- and spreads the disease.
Within the fecal matter of the bug lives an organism known as Trypanosoma cruzi. And if this parasite enters the bloodstream -- perhaps when a sleeping victim wakes up and inadvertently rubs it into the new, itchy wound left by the beetle -- it can lead to Chagas disease, an infection that is both lifelong and life-threatening.
While early symptoms of the illness include nonspecific symptoms such as fever, fatigue, body aches and headache, the chronic phase of the disease can be deadly. At its worst, the disease can lead to heart failure and sudden death.
While most of the 8 to 11 million victims of Chagas live in Mexico and Central America, it is also seen in poor Hispanic households in southern states and along the Mexican border. Exactly how many in the country are infected is a matter of contention; estimates range from a few thousand to up to a million.
Chagas is just one of an array of diseases that disproportionately affect the poor -- and it was one of the diseases highlighted in a recent report titled "Neglected Infections of Poverty in the United States of America."
"The fact that these neglected infections of poverty represent some of the greatest health disparities in the United States, but they remain at the bottom of the public health agenda, is a national disgrace," said Dr. Peter Hotez, author of the analysis and executive director of the Global Network for Neglected Tropical Diseases in a press release.
Reports from the Associated Press contributed to this article.