Tapeworm Infects Man, Gives Him Cancer


Let us never assume that we know anything about anything—especially cancer. Medical understanding of the disease was challenged again this week by a case study published in the New England Journal of Medicine that describes the story of an HIV-positive man who died of cancer he contracted from a tapeworm.

The tapeworm in question, Hymenolepis nana, was uniquely qualified for the job. H. nana is the world’s most common human tapeworm, infecting as many as 75 million people. The parasite’s presence usually doesn’t produce any symptoms; most people don’t even realize they’ve got one.

In addition to its stealth, H. nana has a special talent: sticking around. Every other tapeworm hatches in one host, and then needs to move into another to grow and reproduce. Not H. nana. It can stay put for generations, especially in people with fragile immune systems.

A fragile immune system was what brought the 41-year-old Colombian man to the doctor in the first place. The man had been diagnosed with HIV seven years earlier, but for one reason or another, he had not kept up with his medication. As a result, his immune system was weakened and he was especially susceptible to infection. By the time he came to the clinic, the man was feverish, fatigued, and coughing, and had steadily been losing weight for months.

Doctors found H. nana eggs in the man’s stool, confirming an infection. Tests of his lungs, liver, lymph nodes, and adrenal glands revealed a constellation of tumors ranging in size from 0.16 to 1.7 inches, and biopsies of the tumors revealed something very strange. The tumor cells were malignant and growing, but they were way, way too small to be human. DNA tests confirmed it: The man definitely had cancer … but it wasn’t his. It was his tapeworm’s. The patient passed away just three days later.

To say that this case is unusual would be an understatement. Contagious cancers do exist in dogs and Tasmanian devils, and this year scientists discovered a form of contagious clam leukemia. But as far as we know, cancer doesn’t pass from one species into another. Humans don’t get other animals’ cancer. 

This case was special, says Tommy Leung, a parasitologist at the University of New England. “I don’t think anyone has seen anything like it before,” he said in an email to mental_floss. Leung believes the cancer transmission was possible due to a confluence of three factors: the tapeworm’s endurance; the patient’s compromised immune system; and a mutation in the H. nana larva that transformed run-of-the-mill cancer into an infectious disease.

So should we start freaking out about tapeworm cancer? Absolutely not. It’s possible that this has happened before and been overlooked, paper co-author Peter Olson told IFL Science. "But the report is not that there is a new health risk that people should be worried about," he said.

The Surprising Reason Why Pen Caps Have Tiny Holes at the Top

If you’re an avid pen chewer, or even just a diehard fan of writing by hand, you’re probably well acquainted with the small hole that tops off most ballpoint pen caps, particularly those classic Bic Cristal pens. The reason it’s there has nothing to do with pen function, it turns out. As Science Alert recently reported, it’s actually designed to counter human carelessness.

Though it’s arguably unwise—not to mention unhygienic—to chomp or suck on a plastic pen cap all day, plenty of people do it, especially kids. And inevitably, that means some people end up swallowing their pen caps. Companies like Bic know this well—so they make pen caps that won’t impede breathing if they’re accidentally swallowed.

This isn’t only a Bic requirement, though the company’s Cristal pens do have particularly obvious holes. The International Organization for Standardization, a federation that sets industrial standards for 161 countries, requires it. ISO 11540 specifies that if pens must have caps, they should be designed to reduce the risk of asphyxiation if they’re swallowed.

It applies to writing instruments “which in normal or foreseeable circumstances are likely to be used by children up to the age of 14 years.” Fancy fountain pens and other writing instruments that are clearly designed for adult use don’t need to have holes in them, nor do caps that are large enough that you can’t swallow them. Any pen that could conceivably make its way into the hands of a child needs to have an air hole in the cap that provides a minimum flow of 8 liters (about 2 gallons) of air per minute, according to the standard [PDF].

Pen cap inhalation is a real danger, albeit a rare one, especially for primary school kids. A 2012 study [PDF] reported that pen caps account for somewhere between 3 and 8 percent of “foreign body aspiration,” the official term for inhaling something you’re not supposed to. Another study found that of 1280 kids (ages 6 to 14) treated between 1997 and 2007 for foreign body inhalation in Beijing, 34 had inhaled pen caps.

But the standards help keep kids alive. In that Beijing study, none of the 34 kids died, and the caps were successfully removed by doctors. That wasn’t always the case. In the UK, nine children asphyxiated due to swallowing pen caps between 1970 and 1984. After the UK adopted the international standard for air holes in pen caps, the number of deaths dropped precipitously [PDF]. Unfortunately, it’s not foolproof; in 2007, a 13-year-old in the UK died after accidentally swallowing his pen cap.

Even if you can still breathe through that little air hole, getting a smooth plastic pen cap out of your throat is no easy task for doctors. The graspers they normally use to take foreign bodies out of airways don’t always work, as that 2012 case report found, and hospitals sometimes have to employ different tools to get the stubbornly slippery caps out (in that study, they used a catheter that could work through the hole in the cap, then inflated a small balloon at the end of the catheter to pull the cap out). The procedure doesn’t exactly sound pleasant. So maybe resist the urge to put your pen cap in your mouth.

[h/t Science Alert]

Carnivorous Hammerhead Flatworms Are Invading France

It’s no hammerhead shark, but the hammerhead flatworm has become a real menace in France. Or at least a menace to earthworms, as Earther reports.

Believed to be an invasive species from Asia, the hammerhead flatworm was only recently recorded in France, as is documented in a new study (titled "Giant worms chez moi!") published in the journal PeerJ. However, based on reports, photographs, and videos sent in by citizens across the country, scientists determined the pests have gone undetected for nearly 20 years. This came as a shock, especially because the worms can measure more than a foot in length.

In recent years, three species of the carnivorous worm have quietly taken over French gardens and have even been spotted in metropolitan areas. Some species immobolize their prey with tetrodotoxin, the same powerful neurotoxin that makes pufferfish so poisonous. The worms secrete digestive enzymes, allowing them to dissolve earthworms and slugs their size.

Jean-Lou Justine, co-author of the study, says their eating habits are a concern. "Earthworms are a major component of the soil biomass and a very important element in the ecology of soils," Justine tells Earther. "Any predator which can diminish the populations of earthworms is thus a threat to soil ecology."

Archie Murchie, an entomologist who was not involved in the study, told The Washington Post that the worms will continue to spread in step with global trade. The worms were also seen in overseas French territories, including one worm with a blue-green hue that is probably a newly detected species, Murchie tells the newspaper.

[h/t Earther]


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