Koi pla is a popular dish in northeastern Thailand. It’s made from finely chopped raw fish, mixed with herbs, a dash of lime juice, and a sprinkling of live red ants. Although devoured regularly by many in the Isaan region of the country, the dish actually harbors a deadly secret: it causes liver cancer.

For a long time now, it’s been observed that people in the region have bizarrely high levels of the disease. It’s thought to account for more than half of all male cancer cases in the region, compared to a worldwide average of around just ten percent. And it’s the little freshwater fishies used in the dish that are the culprit, or more specifically, the fluke worms they’re home to. Doctors in the area are trying to educate people as to the risk koi pla poses, reports BBC News Worldwide, and it seems to be working.

“We have been studying this link in our labs for over 30 years,” Dr. Banchob Sripa from the Tropical Disease Research Laboratory in Khon Kaen University told the BBC. “We found that the liver fluke can make a chemical that stimulates a host immune response—inflammation—and after many years, this becomes chronic inflammation, which then becomes cancer.”

Fishing nets set in the Isaan region of Thailand. Credit: Dan Weber/Flickr CC BY-NC-ND 2.0

One of the defining features of cancer is uncontrolled cell division. This can be caused by many different things, such as a simple genetic mutation in the region that regulates the mechanism that keeps cell division in check. Or it could be some sort of chemical or physical irritant that increases the chance that a dividing cell will mutate. When the body is healing, cells in the affected area experience increased rates of division, so if such irritants are present, this creates the opportunity for cell division to get out of control.

When eaten, the flukes found in the tiny fish work their way into the liver. Here they proliferate, growing and laying eggs. These eggs get excreted—often back into the water in which the fish are living—and then eaten by a snail, which is in turn eaten by fish, and thus the cycle starts again.

Once they reach the liver, the flukes release a particular protein that increases cell growth, providing the parasites with a food source. And it is this protein that is the key to the parasite's cancer-causing ability. A few years ago, researchers found that the protein, known as a type of granulin, is almost identical to a human growth hormone. The scientists already knew that different types of granulin can cause uncontrolled cell growth, and after experimentation, they found that the liver fluke protein did exactly the same.

But after over a decade of teaching the locals about the dangers of koi pla, the tide seems to be turning. From infection rates of over 80% in some communities, it seems to be dropping. It is led by the younger people, who now almost always cook the dish before eating it, though there are some older people who appear slightly more stubborn.

“I think 60% do understand the causes of the liver cancer,” Dr. Banchob said to BBC News, “they are aware of the liver fluke. But 10% are still eating raw fish. I believe that 10% probably cannot change. So we should change the environment, make the fish cleaner, to get fewer infections.”

Main image credit: Candice and Jarrett/Flickr CC BY-NC 2.0

This article was amended on 16.06.2015: Liver cancer does not affect half of all men in the region, as oringially stated, but rather accounts for more than half of all cancer cases in men in the region.