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It’s a medical development that seems like something out of a sci-fi movie — even to the people reporting it.

Scientists from the Centers for Disease Control and Prevention have revealed they found tapeworm tumors in an HIV-infected man with a severely weakened immune system.

The growths, which looked like cancer and behaved like cancer, initially confounded the scientists because the cells that made up the masses were far too small to be human.


The 41-year-old patient, who had not been taking medication to control his HIV, lived in Medellin, Colombia. Doctors there knew they were looking at something unusual, but they weren’t sure what. He had growths in his liver, lungs, and some lymph nodes.

“The cells were something like a mix between cancer cells and some kind of parasitic cells,” Dr. Carlos Agudelo, from the Universidad Pontificia Bolivariana, explained in an interview with STAT.


So Agudelo and his colleagues did what doctors the world over do roughly 1,200 to 1,600 times a year. They asked for help from the CDC’s Infectious Diseases Pathology Branch.

This was back in early 2013. From the first medical images sent by the Colombian physicians, Dr. Atis Muehlenbachs knew this was a puzzler.

“It didn’t make sense to what we knew about human cells,” said Muehlenbachs, a CDC pathologist who is lead author of a report on the case published Wednesday in the New England Journal of Medicine.

Hymenolepis nana is the most common tapeworm in humans. Peter Olson/Natural History Museum, London


His team wasn’t clear if the growths were cancer, the work of an infectious agent, or some new and unrecognized pathogen. The leading hunch was that it was some form of protozoa — single-cell life forms, some of which are parasitic.

Testing to explore that theory led to an unexpected answer. Unexpectedly, the test found evidence of DNA from the dwarf tapeworm, Hymenolepis nana.

“And that was the ‘aha’ moment,” Muehlenbachs said. “It was like ‘Holy moly, this is a tapeworm.’”

H. nana is actually the most common tapeworm known to infect people. It is estimated 75 million people around the world carry these worms in their bowels.

People become infested when they eat something contaminated with the tapeworms eggs, which infected humans pass in their stool.

Tapeworms were not thought to develop tumors, which makes the finding more unusual. Muehlenbachs said it may be that when H. nana infects healthy people, the host’s immune system keeps the tapeworm’s tumor-making capacity in check. That was not the case in the man from Medellin, whose immune system had tanked.

Tapeworm Cancer ChestXRay
Chest scans from the 41-year-old patient infected with the dwarf tapeworm revealed lung tumors. Clinica Universitaria Bolivariana

He died in May of 2013, four months after first seeking care. There was no autopsy — a lost opportunity Agudelo rues to this day.

There have been a few similar cases previously reported in the medical literature, but these were all before genetic sequencing technology evolved to the point where scientists could generate the proof the CDC team has in Wednesday’s report.

Dr. David Relman, chief of infectious diseases at the VA Palo Alto Health Care System in California, worked on two earlier cases. One was published in the Lancet in 1996 and the other in the Journal of Infectious Diseases in 2003.

With the first of the two, doctors thought the patient, who also had HIV, was dying of lymphoma, a type of blood cancer. Relman said an astute pathologist at the hospital signaled that the tumor was not made up of human cells.

Relman, who is also a professor of medicine and microbiology at Stanford University, wondered how often this is happening and how often it is missed.

Agudelo and Muehlenbachs do as well, saying they hope the publication will alert clinicians to be on the lookout for this unexpected turn of medical events.