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."
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."
"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.