Scientists have identified the first known case of a man infected with tumors by a common parasitic tapeworm. This case has raised new concerns about more such infections that may go undetected.
Atis Muehlenbachs, lead author of the study and staff pathologist in the US Centers for Disease Control and Prevention's Infectious Diseases Pathology Branch, said, "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. 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."
‘H. nana is the only tapeworm that can complete its entire life cycle in a person's small intestine. Scientists have identified the first known case of a man infected with tumors by this common parasitic tapeworm.’
The case involved a 41-year-old man in Colombia, who was HIV-positive and had not been taking medications. In 2013, he went to his doctors with a cough, fever and complaints of weakness and weight loss. When doctors took biopsies from his lymph nodes and lung tumors, they found some bizarre-looking lesions which looked like human cancer. But initial lab tests showed they were not human. Puzzled, the scientists kept searching for the cause of the man's disease.
The CDC said, "The growth pattern was decidedly cancer like, with too many cells crowded into small spaces and quickly multiplying. 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, the researchers found DNA from Hymenolepis nana, the dwarf tapeworm, in the man's tumor in mid-2013. H. nana is the only one of some 3,000 known tapeworms that can complete its entire life cycle from egg to adult tapeworm in a person's small intestine.
Rarely such tapeworm infections are found outside the small intestine, but in the case of the Colombian man, his weakened immune state may have enabled the parasite's cancer to spread through his body. The study said, "Malignant transformation of H. nana may be misdiagnosed as human cancer, particularly in underdeveloped countries in which HIV and H. nana infections are widespread. The host-parasite interaction that we report should stimulate deeper exploration of the relationships between infection and cancer."
The CDC said, "It is unclear whether human cancer treatments would help in such cases, but urged physicians in developing nations to be aware of the possibility of similar illnesses, especially if they have patients with weakened immune systems who have tumors."
The study is published in the New England Journal of Medicine.