When Kenneth Watson was 16, he thought nothing of the gnat that flew into his eye: "I don't think you can afford to be afraid of bugs in the Bible Belt," he said.
But two weeks later when the Hardy, Ark., teen was getting ready for school, he knew something was terribly wrong when he couldn't see.
When he told his mother, she thought he was faking. "I had slept late and my mom thought I was skipping school," he said. "Sometimes I would come up with crazy stories, and she told me to get up and get ready."
As he walked to the bus stop, Watson waved his hand in front of his face and rubbed his eyes, but all he could see was a large dark dot in the center of his vision. "I keep thinking and thinking, I'm too young to go blind," he said. "Then I freaked out and walked home crying like a baby."
The gnat had laid an egg in Watson's right eye and over a two-week period the parasite hatched and was feeding off the retinal tissue.
"A larva or maggot had been chewing and burning into my eye," said Watson.
The TV series touches on other parasites -– sand flies, worms and parasitic eggs -- that can reproduce in their human hosts and cause blindness, paralysis, brain damage and even death.
"Some of these experiences are rare, especially in North America, but they can happen to anyone," said biologist and zoologist Dan Riskin, who leads the scientific discussion on the show. "Parasites are in the food we eat, in the water we swim (in) and on the ground we walk. They are lurking in the shadows, waiting for just the right moment to take host."
But Watson's case is not that unusual, according to Dr. Peter Hotez, a parasite specialist and chairman of the Department of Microbiology, Immunology and Tropical Medicine at The George Washington University.
Known as ocular myiasis, the condition affects "a couple of thousand" of Americans a year, said Hotez, usually in the southern states.
"It's deposited as an egg and then it catches up to you and becomes fairly large," he said. "It's not as rare as you think. Maggots can actually cause tissue damage when they go into an open wound, which is the most common form [of myiasis]."
Unlike Watson, those who are affected tend to the homeless, alcoholics or others who can't take care of their health and may be exposed to the elements.
There are hundreds of parasites, but only about a half dozen in the United States, according to Hotez.
"In the U.S., there are a whole host of 'infections of poverty,'" he said. "It's an overwhelming determinant. Parasites flourish in poor sanitation or when there is no indoor screening or air conditioning."
Watson was lucky that his mother rushed him to the doctor. Images of his eye revealed hemorrhages and a minor blood clot blocking the optic nerves. But the doctor couldn't tell what was causing it.
"He asked me how fast I could get to the Charles Retina Institute in Memphis – that was three hours away," said Watson. "They wanted to see me immediately."
"On the way there, I started to calm down and cope," he said. "I knew I was headed somewhere to get help. I was cracking jokes, like saying I was going to get a glass eye. My mom didn't like that."