In January 2013, a 41-year old man went to a hospital in Colombia complaining of fatigue, fever, cough and weight loss. The doctors discovered his body was riddled with tumors.
But that was where the case grew strange: Though the cells grew like cancer (quickly and out-of-control) their small size (about 10 times too small) and tendency to fuse together was unlike any human tumor, reports Ariana Eunjung Cha for The Washington Post.
It took months of tests before the Centers for Disease Control and Prevention was able to find the culprit, reports Loren Grush for The Verge. Eventually DNA analysis revealed that the man had been infected with cells from a dwarf tapeworm, or Hymenolepis nana. But the patient died from kidney failure just three days after the diagnosis.
Although this particular case is odd and horrifying, tapeworms don’t usually cause cancer. Typically, when playing host to a tapeworm "[m]ost of the time you wouldn’t even know it was there," Peter Olson, a tapeworm expert at the Natural History Museum in London, tells The Verge.
So how did this happen?
People pick up tapeworms by eating food that contains the worms' eggs. Once inside their host, tapeworm larvae burrow into the lining of the intestine and then grow into the adult form.
Usually, a healthy immune system keeps the tapeworm from invading the rest of the body (except in very rare cases). But this particular patient was also infected with HIV and had not been taking medications, so his immune system was weakened.
The suppressed immune system allowed cells from the tapeworm to travel through the man’s body. But how the tapeworm eggs went from parasite to cancer is less clear, Cha reports. Did the eggs start as cancerous masses or did something spark this development as they brewed?
Though the case is unusual, it does worry some experts.
With a few exceptions, cancer isn’t usually consider a transmittable disease. So although a frightening concept, people probably can't get cancer from another person infected with tapeworms, Cha reports. Yet tapeworm infections are common throughout the world and could pose more of a danger to people with weakened immune systems than previously thought.
Scientists have much more to learn about the biology of parasites and cancer—could other parasites develop cancer and transfer the malignant cells to humans? Since the man died before any treatment for the tapeworm could be attempted, another remaining unknown is how to treat such a case of cancer.
For this first patient, the lack of information proved deadly. "It was heartbreaking," CDC pathologist Atis Muehlenbachs tells Rae Ellen Bichell for NPR.