Villagers in this poverty-stricken farming communities are passionate about their food, especially the traditional varieties of fermented fish that one aficionado describes as tasting like heaven but smelling like hell.
It can be a fatal attraction, medical researchers say. The raw fish that is so avidly consumed in the stilt houses that sit among rice paddies and wetlands of the country’s northern provinces contain parasites that can accumulate in the liver and lead to a deadly cancer. Known as bile duct cancer, it is relatively uncommon in most parts of the world but represents the majority of the 70 liver cancer deaths a day in Thailand, according to Dr. Banchob Sripa, the head of the tropical disease research laboratory at nearby Khon Kaen University.
“It’s the most deadly and persistent cancer in the region,” Dr. Banchob said.
For the past three decades, he has led an unsuccessful campaign against the parasite, known as a liver fluke and which is also endemic in Cambodia, Laos, Vietnam, parts of China, the Korean Peninsula and Siberia.
Dr. Peter Hotez, the president of the Sabin Vaccine Institute, a nonprofit organization in the United States that researches neglected tropical diseases, describes liver flukes as one of “the most important infectious causes of cancer that no one has ever heard of.”
Cooking the fish would eliminate the risk of infection. But the battle against liver flukes is being undermined in Thailand by a deeply ingrained love of the sour and smoky-tasting fermented dishes that generations of villagers have relished.
Some villagers just cannot break the habit, said Nutcharin Yanarangsri, a volunteer at a government health clinic in the village here who spends her days walking from house to house with a singular message: “Say no to raw fish!”
“We tell them, ‘If you really want to eat it, you’d better boil it or cook it,”’ Ms. Nutcharin said during one of her rounds through the village. “But they tell me, ‘Eating it raw is so delicious. I can’t stop. I love it!”’
Whether it is a green papaya salad with just the right mix of sweet and sour or a duck curry swimming in spices, the cuisine of Thailand is a national passion. The country’s 65 million people seem to spend their waking hours either talking about food or consuming it.
But the Thai love of food has a masochistic side. It is not uncommon for office workers to lunch on searingly hot chili-laced dishes only to rush to the bathroom a few hours later with a bad case of Bangkok belly.
The love of fermented foods, especially in northeastern Thailand, is the extreme version of this gourmand obsession — and that love is often heedless of the consequences.
One popular dish in northeast Thailand is called pla som, or sour fish, which is made by mixing raw fish, garlic, salt, steamed rice and a pinch of seasoning powder. The mixture is shaped into egg-size portions, put into plastic bags and left to sit in the tropical heat for three days. That is not nearly long enough to kill the parasites, which die only after at least six months of fermentation.
Liver flukes are present only in fresh water, but they are not found everywhere. The rate of infection in Bangkok, a five-hour drive away, is close to zero.
Transmitted through feces, the parasites thrive in rural areas without proper sanitation, and they rely on snails, fish, cats and humans as hosts. Yet villagers do not see fermented fish as a dangerous thrill.
This is not analogous to the tradition in Japan of eating fugu, the puffer fish that is potentially toxic when prepared the wrong way.
The deadly effects of eating parasite-infected raw fish accumulate over decades, in the same way that drinking large amounts of alcohol over a lifetime can damage one’s liver. (Heavy drinking increases the chance of bile duct cancer for those infected with the parasite, Dr. Banchob said.
Somewhere between 1 percent and 5 percent of people infected with the parasites contract liver cancer.
Laos, Vietnam and Cambodia also have high rates of liver cancer, according to statistics from the United Nations. Dr. Banchob estimates that about 10 percent of the population in Laos is infected with liver flukes.
Dr. Hotez of the Sabin Institute said that the parasite is similar to other worms and ailments that get less attention because they rarely afflict wealthy urban populations. “Even though Thailand is a middle-class country, there are still pockets of intense poverty — and with that poverty come high rates of neglected tropical diseases,” Dr. Hotez said. “We’ve got the technology to make vaccines. But we don’t have the funding.”
Dr. Cherdchai Tontisirin, a surgeon in Khon Kaen who has operated on liver cancer patients, blames the Thai government for the persistence of the disease. More could be done to make sure villagers stop eating raw fish, he said.
“The government has never taken this seriously,” Dr. Cherdchai said. “This is a disease that affects only the north and the northeast, and these are regions that have been forgotten for a long time.”