For the first time, cancer that developed in a tapeworm has been found to cause a tumor in its human host. The discovery has been met with wonder and concern in equal measure.
Researchers at the Centers for Disease Control and Prevention (CDC) have solved an incredible mystery that began in Colombia and took almost 3 years of research to unfurl.
Investigator’s at the CDC’s Infectious Diseases Pathology Branch (IDPB) discovered that a patient’s strange cancer-like tumors had initially developed as cancer cells within a tapeworm (Hymenolepis nana).
Dr. Atis Muehlenbachs, lead author of the study, published this month in the New England Journal of Medicine, explains his surprise:
“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.”
The story began in Colombia in 2013. Doctors found unusual tumor cells in the lungs and lymph nodes of a 41-year-old HIV-positive patient.
The medical team was unable to make sense of the biopsies. The cells looked like cancer cells – but none that they had ever encountered before.
The cells multiplied quickly and were crammed into a small space, as cancer cells normally are. But, the individual cells were around 10 times smaller than standard human cancer cells, and some were fused together, which is rare behavior for human cells.
The Colombian medical team sent samples of the peculiar tumor to the CDC for further investigation.
The IDPB dedicated large tracts of time to hunting down the origin of these cellular oddities. Eventually, they tracked the DNA down to H. nana. This was their eureka moment. Sadly, however, the patient died 72 hours later.
Also known as the dwarf tapeworm, H. nana is a transparent platyhelminth measuring up to 40 mm long and 1 mm wide. It is particularly common in temperate regions and where sanitation and clean water are not readily available.
Of the 3,000 types of tapeworm known to utilize animal hosts, H. nana is the most common tapeworm found infecting humans globally.
The worm moves into human hosts through food infected by rodent droppings or insects, or more commonly, by accidentally ingesting the feces of another infected person.
H. nana is the only known tapeworm that can complete its entire lifecycle within the small intestine of a human.
This single host approach is one of the prime reasons why H. nana is such a successful parasite; it does not have to concern itself with releasing itself or its eggs from the safety of the human’s interior. The adaptation is thought to be relatively recent, as H. nana are still capable of developing normally in larval fleas and beetles should the need arise.
The parasite’s ability to replicate, grow and breed inside a human is particularly important in people with a compromised immune system. Without the faculties to fight the parasite, a huge number can grow and survive in the guts of an infected patient.
As we speak, there are around 75 million people infected by H. nana.
Another reason for the dwarf tapeworm’s global success is the effect it has on its human host: very little. In general, the carrier will not be aware of the infection at all.
Although this could be an isolated case, it does raise concerning questions. Researchers believe that this type of tumor transfer is only likely to occur in people with compromised immune systems, but due to the prevalence of H. nana in countries where there are also a large number of people with HIV, it certainly deserves further research.
On a more positive note, it could open up new avenues of investigation into the ways in which cells can become cancerous.
In other news about how parasites are aiding research into cancer, Medical News Today recently reported on a study about a malarial protein’s potential use in the treatment of cancer.