Stunned scientists described on Wednesday the first known case of a man infected with tumors by a common parasitic tapeworm, raising concern about more such infections that may go undetected.
"We were amazed when we found this new type of disease -– tapeworms growing inside a person essentially getting cancer that spreads to the person, causing tumors," said Atis Muehlenbachs, staff pathologist in the US Centers for Disease Control and Prevention's Infectious Diseases Pathology Branch.
"We think this type of event is rare. 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," added Muehlenbachs, lead author of the study in the New England Journal of Medicine.
The case involved a 41-year-old man in Colombia. He was HIV-positive and not been taking medications when in 2013, he went to his doctors with a cough, fever and complaints of weakness and weight loss.
His doctors took biopsies from his lymph nodes and lung tumors, and appealed to the CDC for help in diagnosing some bizarre-looking lesions which looked like human cancer, but initial lab tests showed they were not human.
Puzzled, scientists kept searching for the cause of the man's disease.
"The growth pattern was decidedly cancer like, with too many cells crowded into small spaces and quickly multiplying," the CDC said in a statement.
"But the cells were tiny -- about 10 times smaller than a normal human cancer cell. The researchers also noticed cells fusing together, which is rare for human cells."
After dozens of tests, they found DNA from Hymenolepis nana, the dwarf tapeworm, in the man's tumor in mid-2013.
The man died soon after.