Late last summer, Rosemary Alvarez of Phoenix thought she had a brain tumor. But on the operating table her doctor discovered something even more unsightly -- a parasitic worm eating her brain.
Alvarez, 37, was first referred to the Barrow Neurological Institute at St. Joseph's Hospital and Medical Center in Phoenix with balance problems, difficulty swallowing and numbness in her left arm.
An MRI scan revealed a foreign growth at her brain stem that looked just like a brain tumor to Dr. Peter Nakaji, a neurosurgeon at the Barrow Neurological Institute.
"Ones like this that are down in the brain stem are hard to pick out," said Nakaji. "And she was deteriorating rather quickly, so she needed it out."
Yet at a key moment during the operation to remove the fingernail-sized tumor, Nakaji, 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."
When Alvarez awoke, she heard the good news that she was tumor-free and she would make a full recovery. But she also heard the disturbing news of how the worm got there in the first place.
Nakaji said someone, somewhere, had served her food that was tainted with the feces of a person infected with the pork tapeworm parasite.
"It wasn't that she had poor hygiene, she was just a victim," said Nakaji.
"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."
The pork tapeworm has plagued people for thousands of years. The parasite, known as cysticercosis, lives in pork tissue, and is likely the reason why Jewish and Muslim dietary laws ban pork.
Kuhn said whether you get a tapeworm in the intestine, or a worm burrowing into your brain can depend on how you consumed the parasite.
Eat the parasite in tainted meat and you'll end up eating the larvae, called cysts. Kuhn said in that case, a person can only end up with a tapeworm.
"You can eat cysts all day long and it won't get into your brain," said Kuhn. Instead, the larvae go through the stomach and mature in the intestine.
"When it gets down into their small intestine, it latches on, and then it starts growing like an alien," said Kuhn.
Once there, the tapeworm starts feeding and gets to work. A single tapeworm will release 50,000 eggs a day, most of which usually end up in the toilet.
"They can see these little packets pass in their feces," said Kuhn. "And ... sometimes people eat the eggs from feces by accident."
Kuhn said it is then feces-tainted food, and not undercooked pork, that leads to worms burrowing into the brain.
Unlike the cysts, the eggs are able to pass from the stomach into the bloodstream. From there, the eggs may travel and lodge in various parts of the body -- including the muscle, the brain or under the skin -- before maturing into cysts themselves.
According to Kuhn, who has traveled to study this parasite, cysticercosis is a big problem in some parts of Latin America and Mexico where health codes are hard to enforce and people may frequently eat undercooked pork.