Tapeworm Gives Man the Cancer That Kills Him
Scientists have discovered the first case in which the common parasite transmitted cancer to a human host.
Photo Credit: Shutterstock / Jubal Harshaw
Humans and tapeworms have had a fairly acrimonious relationship for about two million years, which is how long ago researchers suspect we’ve unhappily coexisted. Over the millennia, humans have come to learn how tapeworms enter our systems, develop in our bodies, and can and can’t harm us. At least, that’s what we thought. Until recently, when for the very first time, scientists identified a case in which a tapeworm transmitted cancer to its human host. The odd story has researchers scratching their heads, wondering what we may now need to learn about both tapeworms and cancer.
In a report from the Centers for Disease Control, researchers describe the unusual circumstances involved in the case and how they arrived at a diagnosis. It began in 2013, when doctors in MedellĂn, Colombia, began treating an HIV positive man who had been getting progressively sicker for months. The doctors noted that he was infected with Hymenolepis nana, or the dwarf tapeworm. They also observed tumors throughout his lungs, liver and adrenal glands, which they suspected were cancerous. But a biopsy revealed oddities that suggested, in the words of researchers, “a nonhuman origin.” So they got the CDC involved.
Atis Muehlenbachs, a CDC pathologist, confirmed that the samples received seemed odd. "They were way too small to be human," Muehlenbachs told CBS News. "They were actually about 10 times smaller than a human cancer cell."
Initially, researchers were at a loss, and assumed they might be dealing with an all-new, never before seen disease. Muehlenbachs says he thought perhaps they had encountered “a weird human cancer or some unusual, bizarre emerging protozoa-amoeba-like infection.” But then, tests revealed dwarf tapeworm DNA in the tumors.
“And that was the aha moment,” Muehlenbachs tells STAT News. “It was like, holy moly, this is a tapeworm."
The patient died soon after, but scientists continued to investigate the case. According to the CDC, the dwarfm tapeworm is the most prevalent type of human tapeworm. The parasite infects an estimated 75 million people around the world and up to 25 percent of the children in some populations. Infection is generally asymptomatic. Though there’s little need for public panic, those stats show there is a pressing need to seek out more information. Researchers emphasize that the patient in this case had an extremely compromised immune system, which may have contributed to the transmission of cancerous cells.
"We think this type of event is rare," Muehlenbachs tells NBC News. "However, this tapeworm is found worldwide and millions of people globally suffer from conditions like HIV that weaken their immune system. So there may be more cases that are unrecognized. It's definitely an area that deserves more study."
Bobbi Pritt, director of clinical parasitology at the Mayo Clinic, added this bit, which promises to keep some of us up at night: “H. nana is a very common tapeworm infection in humans, and therefore I would expect there to be other cases like the one described…that were misdiagnosed or went undetected.”
Speaking with the Washington Post, London Natural History Museum researcher Peter D. Olson, who also contributed to understanding the findings, says the discovery represents “an enormous advance in our knowledge and raises questions about the conditions under which cells may become cancerous."
Interestingly, STAT News notes that this is not the first time scientists have identified cancer cases involving non-human cells. However, two previous cases occurred before technology could accurately identify what researchers were looking at. The CDC study is available online.
