KALASIN (Thailand) • It was not until he got to medical school that Dr Narong Khuntikeo finally discovered what caused the liver cancer that took both of his parents' lives: their lunch.

Like millions of Thais across the rural north-east, his family regularly ate koi pla - a dish made of raw fish ground with spices and lime.

The pungent meal is quick, cheap and tasty, but the fish is also a favourite feast for parasites that can cause a lethal liver cancer, killing up to 20,000 Thais annually.

Most hail from the north-east, a large, poor region known as Isaan where people have dined on koi pla for generations and now has the highest reported incidence of cholangiocarcinoma (CCA) - bile duct cancer - in the world.

One of the major causes of CCA is a parasitic flatworm - or fluke - which is native to the Mekong region and found in many freshwater fish.

Once eaten, the worms can embed undetected in the bile ducts for years causing inflammation that can, over time, trigger the aggressive cancer, according to the World Health Organisation.

"It's a very big health burden around here... it affects families, education and socio-economic development," said Dr Narong, who went on to become a liver surgeon to battle the scourge.

"But nobody knows about this because they die quietly, like leaves falling from a tree."

After seeing hundreds of hopeless late-stage cases on the operating table, Dr Narong is now marshalling scientists, doctors and anthropologists to attack the "silent killer" at the source.

They are fanning out across Isaan provinces to screen villagers for the liver fluke, and warn them of the perils of koi pla and other risky fermented fish dishes.

But changing eating habits is no easy task in a region where the love for Isaan's famously chilli-laden cuisine runs deep.

Health officials are pinning their hopes on the next generation, targeting children with a new school curriculum that uses cartoons to teach them the risks of eating raw fish.

For the elderly, the target is to catch infections through screening before it is too late.

Dr Narong and his team have developed urine tests to detect the presence of the parasite, which has infected up to 80 per cent of some Isaan communities.

They have also spent the past four years trucking ultrasound machines around the region to examine the livers of villagers who live far from public hospitals.

AGENCE FRANCE-PRESSE