Bizarre, Unwanted HouseGuests

"In the initial months, we wondered if this was a weird human cancer or some unusual, bizarre emerging protozoa-amoeba-like infection."
"This is the first time we've seen parasite-derived cancer cells, spreading within an individual. This is a very unusual, very unique illness."
Atis Mueholenbachs, specialist pathologist, U.S. Centers for Disease Control & Prevention

Unusual because the patient, a 42-year-old Colombian man, was struggling with HIV-AIDS. That condition famously depresses the human immune system. He had picked up somewhere a common form of tapeworm, and it grew unchecked in his body since his immune system was compromised and wasn't able to react. Possibly because it had free reign and was well established it began to mutate, and the tapeworm's cells turned cancerous. As a hypothesis, it's as good as any.

E1KHFK Artwork of an intestinal tapeworm.

In one field of medical science tapeworms are being increasingly used to treat people for various maladies, just as live maggots or leaches are sometimes prescribed to clean up infections; it helps considerably not to be squeamish, one supposes, about such little helpers. But the recent discovery of a tiny tapeworm leading to a situation where cancer crossed species rings a loud, clanging note of caution. It may not be such a terrific idea to use tapeworms for migraines or bowel problems, after all.

Not that the Colombian man deliberately permitted tapeworms entry to his body through one of the popularized new medical treatments. The tapeworm in question is a subspecies known to infect some 75-million people worldwide, and it is called Hymenolpis Nana. The scientists at CDC thought the man could have swallowed microscopic tapeworm eggs in contaminated food. Once introduced into his gastrointestinal tract the swiftly multiplying tapeworms also invaded other parts of his body.

Up to the present time, scientists felt confident that parasites known to invade the human body would not be carriers of cancer cells, much less have the ability to somehow transfer those cancerous cells to the people in whom they dwell. But this man developed numerous large tumours in different parts of his body. When the tumours were biopsied it was discovered their cells behaved just as cancer cells do in their destructive effect.

But they did stand out in other respects as being different. They were much smaller than normal human cancer cells. So the doctors looked to the U.S. Centers for Disease Control and Prevention for possible assistance. And Atis Muehlenbachs, a pathologist working in the unit investigating unexplained mystery illnesses and deaths applied himself to working out the puzzle.

And it was a puzzle that he and his colleagues lent their attention to when the cell samples arrived two years ago. The growth pattern of the cells replicated just like cancer, demonstrating overcrowding and a huge multiplication rate. Yet unlike human cancer cells, those cells fused together. Early on it was thought these cells could represent a new form of infectious organism.

Until the scientists made the discovery that the cells contained DNA identification of a dwarf tapeworm, Hymenolepis nana. A research and tapeworm expert at the Natural History Museum in London was tasked to add his knowledge in identifying the DNA samples, and verified that the analysis linking to the tiny tapeworms was accurate.

This discovery, published this week in the New England Journal of Medicine, has served to raise other concerns as well. Now that it is known that cancerous cells can be present in tapeworms, what about mutant cells living within or on people invaded by other organisms; might they too not be a vector for the transmission of cancer cells? The human body is rife with symbiotic organisms, our guts rely on them to process energy.