The Researcher Who Let a Sand Flea Live in Her Foot

Now is the time to check out the crawling sensation near your toe.

A sand flea pupa. (Wikimedia commons)

There’s a proud tradition of scientists conducting experiments on themselves: Jonas Salk injected his entire family with the first polio vaccine. Sir Humphry Davy inhaled the fumes he concocted in his chemistry lab. The German physician Werner Forssmann stuck a catheter in his own heart.

But the fact that these gonzo studies sometimes end tragically (Jean-François Pilâtre de Rozier pioneered flight in hot air balloons and later died in one) tends to dissuade most researchers from trying.

But, there are still people like Marlene Thielecke, a PhD student in tropical medicine at Charite University Medicine in Berlin. Thielecke is interested in the sand flea, or Tunga penetrans, a parasite that plagues people living in the Caribbean, South America, and parts of Africa. Female sand fleas burrow into the skin, leaving just a tiny opening to the outside world through which it poops, breathes, and pushes out a creamy white fluid filled with eggs. In places with little available medical care, the condition it causes—called tungiasis—leads to not only unbearable itching, but also secondary infections that make it hard to walk. Sufferers sometimes try to dig out the fleas using unsterilized instruments, leading to even more severe infections and sometimes death.

It’s been a problem for centuries without much in the way of a cure, making tungiasis what’s known as a neglected disease. In his book Three Years in Savage Africa, published in 1900, Lionel Decle wrote, "I found the people starving, as they were so rotten with ulcers from jiggers that they had been unable to work in their fields, and could not even go to cut the few bananas that had been growing.”

Thielecke was living in central Madagascar, prime sand-flea country, for an eight-month stretch in 2011. While working with people who were suffering from tungiasis, Thielecke herself fell prey to a sand flea that tunneled deep into the sole of her right foot.

A person with advanced tungiasis.
(Wikimedia Commons.)

And then, she left it in there.

“But why would you just ... leave it in?” I asked, remembering all the times I’ve walked an extra two city blocks to avoid a grasshopper who may or may not have had thoughts of jumping on me.

“I saw that it wasn't harming me at all, so I decided to leave it to observe the stages of the flea,” Thielecke told me by phone.

She had a tetanus vaccine, so more serious infections weren’t a worry, and she knew she could easily extract it if she needed to. Besides, many of the people in her village had hundreds of sand fleas, scarring and sometimes nearly crippling them.

“To the people who really have it, one is a joke,” she said. “One is nothing.”

Thielecke's foot, with the sand flea on the day she
discovered it, and then after 18, 34, 46, 60, and 61 days.
(Travel Medicine)

Thielecke knew that the sand fleas tend to attract each other, though, so she made sure to wear shoes and socks every day to avoid getting another flea. And she didn’t really mention it to anyone in the village.

“For me, it was not a big issue,” she said, taking the record for the statement I can least relate to from any interview ever. “I knew it couldn’t harm me.”

Over the next few months, Thielecke observed her flea as it grew to a rather hefty 1 cm in size. But she noticed something strange: It wasn’t dying, as the fleas typically do after about four to six weeks, and it also wasn’t expelling any eggs.

This fact helped Thielecke understand that it hadn’t reproduced—most likely because she kept the flea separated from its male suitors and in a permanent, single-girl-in-the-foot-city “waiting period,” as she called it. It also taught her something about the sand flea reproductive style: The males find the clusters of females, hidden alluringly just beyond a thin layer of skin, and make their move.

“The single embedded sand flea remained a virgin,” Thielecke wrote. The results of her self-made sand flea experiment were published last month in Travel Medicine.

This won’t necessarily help prevent sand flea scourges in countries like Madagascar, Thielecke and her supervisor, Hermann Feldmeier, told Science magazine, but it might help people who are already host to one flea avoid getting more.

After six weeks with her flea, Thielecke was in pain and found it hard to walk, so she had it surgically removed. The virgin flea left her just as it had entered, without much of a thought. Thielecke said the important thing was that her experiment doesn’t distract from an ailment that afflicts up to half the population in some countries.

“There are very many people really suffering from this,” she said. “My experiment is a very small spot in this big disease.”