Breaking Update: Here’s a clear explanation of the latest developments related to Breaking News:Foodborne trematode infections: Parasitic worms causing liver and lung disease– What Just Happened and why it matters right now.
Somchai loved his grandmother’s traditional Thai dish—koi pla, raw fish salad seasoned with lime, chili, and herbs. It was a specialty in his village in northeastern Thailand, prepared for celebrations and family gatherings. The fish came fresh from local ponds, the recipe passed down through generations.
But at age 35, Somchai began experiencing persistent abdominal pain. His skin turned yellow. He lost weight rapidly. At the provincial hospital, doctors found his liver was severely damaged. An ultrasound revealed something shocking: dozens of parasitic worms—liver flukes—living in his bile ducts.
“The raw fish,” the doctor explained. “You’ve been infected for years, probably since childhood. These parasites have been damaging your liver all this time.” Then came the devastating news: the chronic infection had developed into cholangiocarcinoma—bile duct cancer. Despite treatment, Somchai died six months later, leaving behind a wife and two young children.
Somchai’s tragedy reflects a global health problem. According to WHO’s work on foodborne trematode infections, foodborne trematodes are a group of diseases that include the parasites Clonorchis, Opisthorchis, Fasciola and Paragonimus. These parasitic flukes cause infection in humans via the consumption of contaminated food (raw fish, crustaceans or vegetables). Infection can result in severe liver and lung disease and together these diseases are estimated to cause 2 million life years lost to disability and death worldwide every year.
For more on parasitic infections, see our articles on neglected tropical diseases and foodborne illnesses at ObserverVoice.com.
The Four Main Parasites
Foodborne trematodes have a complex life cycle involving diverse definitive hosts and one or two intermediate hosts. These parasitic flukes infect humans through contaminated food, causing different diseases depending on the species.
Clonorchis and Opisthorchis (liver flukes) species have adult flukes that lodge in the smaller bile ducts of the liver, resulting in inflammation and fibrosis of surrounding tissues. WHO’s Q&A on clonorchiasis and opisthorchiasis provide detailed information. Chronic infection can result in cholangiocarcinoma, a fatal bile duct cancer. Both C. sinensis and O. viverrini are classified as carcinogens.
WHO provides maps showing global distribution of clonorchiasis and global distribution of opisthorchiasis, showing high-risk areas primarily in East and Southeast Asia.
Fasciola (liver flukes) adult worms lodge in larger bile ducts and gall bladder resulting in inflammation, fibrosis, blockage, colic pain and jaundice. WHO’s Q&A on fascioliasis explains transmission and symptoms. Chronic infection can result in liver cirrhosis. WHO published Fasciola: background document for WHO guidelines for drinking-water quality in March 2025. The global distribution of fascioliasis shows infections occur worldwide, particularly in areas with livestock farming.
Paragonimus (lung flukes) species have their final location in the lung tissue, resulting in a chronic cough, blood-stained sputum, chest pain, dyspnoea (shortness of breath) and fever. WHO’s Q&A on paragonimiasis provides comprehensive information. These symptoms can be confounded with tuberculosis. Adult worms may also infect extra-pulmonary locations such as the brain and can result in symptoms of headaches, mental confusion, convulsions and cerebral haemorrhage. The global distribution of paragonimiasis shows the disease occurs across Asia, Africa, and Latin America.
WHO’s fact sheet on foodborne trematode infections provides detailed information on all four diseases. WHO also published operational guidelines for the elimination of human fascioliasis as a public health problem in the Americas in July 2024.
For more on related parasitic diseases, see our articles on neglected tropical diseases at ObserverVoice.com.
Silent Disease with Devastating Consequences
The public health burden due to foodborne trematodiases is predominantly due to morbidity rather than mortality with early and light infections often going unnoticed. Chronic infections are associated with severe morbidity with symptoms reflecting the organ in which the adult worms are located.
Acute or early infection with Clonorchis or Opisthorchis may result in non-specific gastrointestinal symptoms that people often ignore. Years or decades later, chronic infection causes serious liver damage and can result in cholangiocarcinoma, a fatal bile duct cancer. WHO created an infographic on Opisthorchiasis or Liver Fluke illustrating the disease cycle.
Dr. Paiboon Sithithaworn, a parasitologist who has studied liver flukes in Thailand for decades, explained the tragedy: “People eat raw fish for years, enjoying their cultural traditions. They don’t know they’re infected. By the time symptoms appear—jaundice, abdominal swelling, weight loss—the cancer has often already developed. We see patients in their 30s and 40s dying from this preventable disease.”
In July 2020, WHO reported that children are the key to behaviour change to reduce infection, highlighting the importance of educating young people about safe food practices.
WHO’s map of global distribution of foodborne trematodiases, 2010-2019 shows the extensive geographic spread of these infections.
Treatment and Prevention
Treatment of foodborne trematodiases is important to prevent progression of clinical disease and reduce associated morbidity. Treatment can be offered through preventive chemotherapy or individual case management.
Preventive chemotherapy involves a population-based approach where everyone in a given region or area is given medicines, irrespective of their infection status. This is recommended in areas where large numbers of people are infected. Praziquantel is recommended for treatment of clonorchiasis and opisthorchiasis while triclabendazole is recommended for fascioliasis. Both praziquantel and triclabendazole can be used for treatment of paragonimiasis.
WHO provides forms to request donated praziquantel for the treatment and control of clonorchiasis and opisthorchiasis. WHO also provides application for donated triclabendazole for fascioliasis treatment.
Individual case-management involves the treatment of people with confirmed or suspected infection. This approach is more appropriate where cases are less clustered and where health facilities are available.
Treatment should be complemented by interventions that reduce transmission such as education on safe food practices, improved sanitation and veterinary public health measures.
In July 2018, WHO announced renewed medicine donation to sustain global fight against liver infection, ensuring continued access to essential medicines.
For more on treatment strategies, see our articles on tropical disease control at ObserverVoice.com.
WHO’s Comprehensive Approach
WHO coordinates multiple activities to combat foodborne trematode infections through its Neglected Tropical Diseases program.
WHO’s activities include promoting prevention and control using a One Health approach, promoting joint implementation with other NTD interventions, supporting countries in their control efforts, and improving data and identifying endemic and high-risk areas.
In December 2017, WHO featured how Thailand uses integrated ecosystems health approach to beat cancer-causing disease, demonstrating successful control strategies.
In July 2018, WHO reported that a review provides fresh perspectives on infection and control of human fascioliasis.
WHO published Taenia solium: use of existing diagnostic tools in public health programmes in November 2022, addressing related parasitic infections including taeniasis and cysticercosis.
The World Health Assembly adopted Resolution WHA31.48 on Prevention and control of zoonoses and foodborne diseases due to animal products in 1978, establishing foundational commitments.
Somchai’s village has changed since his death. His widow works with health officials, teaching villagers about the risks of raw fish. “My husband loved that dish,” she said. “But it killed him. Now I tell everyone—cook your fish. It still tastes good, and you won’t get cancer.” The village temple displays posters showing how liver flukes infect humans, and schoolchildren learn about safe food preparation.
With WHO’s comprehensive approach to foodborne trematode infections, the 2 million life years lost annually can be dramatically reduced—proving that simple changes in food preparation can save lives and prevent cancer.
For more information, visit WHO’s foodborne trematode infections health topic page or explore related content at ObserverVoice.com.
Frequently Asked Questions (FAQs)
1. What are foodborne trematode infections and how common are they?
According to WHO’s work on foodborne trematode infections, foodborne trematodes are a group of diseases that include the parasites Clonorchis, Opisthorchis, Fasciola and Paragonimus. These parasitic flukes have a complex life cycle involving diverse definitive hosts and one or two intermediate hosts. Foodborne trematodes cause infection in humans via the consumption of contaminated food (raw fish, crustaceans or vegetables). Infection can result in severe liver and lung disease and together these diseases are estimated to cause 2 million life years lost to disability and death worldwide every year. The public health burden is predominantly due to morbidity rather than mortality with early and light infections often going unnoticed. Chronic infections are associated with severe morbidity with symptoms reflecting the organ in which the adult worms are located. WHO’s fact sheet on foodborne trematode infections provides comprehensive information. WHO’s map of global distribution of foodborne trematodiases, 2010-2019 shows extensive geographic spread. WHO’s Neglected Tropical Diseases program coordinates control efforts. See our articles on parasitic infections.
2. What symptoms do the different types of foodborne trematode infections cause?
Clonorchis and Opisthorchis species have adult flukes that lodge in the smaller bile ducts of the liver, resulting in inflammation and fibrosis. Acute or early infection may result in non-specific gastrointestinal symptoms. Chronic infection can result in cholangiocarcinoma, a fatal bile duct cancer. Both C. sinensis and O. viverrini are classified as carcinogens. WHO’s Q&As on clonorchiasis and opisthorchiasis provide details. Fasciola adult worms lodge in larger bile ducts and gall bladder resulting in inflammation, fibrosis, blockage, colic pain and jaundice. Chronic infection can result in liver cirrhosis. WHO’s Q&A on fascioliasis explains symptoms. The final location of Paragonimus species is in the lung tissue, resulting in chronic cough, blood-stained sputum, chest pain, dyspnoea and fever. These symptoms can be confounded with tuberculosis. Adult worms may infect the brain causing headaches, mental confusion, convulsions and cerebral haemorrhage. WHO’s Q&A on paragonimiasis provides information. WHO created an infographic on Opisthorchiasis or Liver Fluke. See our articles on liver diseases.
3. Where do these infections occur and how are they transmitted?
Foodborne trematodes cause infection via consumption of contaminated food (raw fish, crustaceans or vegetables). WHO provides distribution maps: global distribution of clonorchiasis showing high-risk areas in East and Southeast Asia; global distribution of opisthorchiasis also concentrated in Asia; global distribution of fascioliasis showing worldwide distribution particularly in livestock farming areas; and global distribution of paragonimiasis across Asia, Africa, and Latin America. These parasitic flukes have complex life cycles involving diverse hosts and one or two intermediate hosts. WHO published Fasciola: background document for WHO guidelines for drinking-water quality March 2025. WHO published operational guidelines for elimination of fascioliasis in the Americas July 2024. WHO reported children are key to behaviour change July 2020. See our articles on food safety.
4. How are foodborne trematode infections treated?
Treatment of foodborne trematodiases is important to prevent progression of clinical disease and reduce associated morbidity. Treatment can be offered through preventive chemotherapy or individual case management. Preventive chemotherapy involves a population-based approach where everyone in a region is given medicines, irrespective of infection status. This is recommended in areas where large numbers are infected. Praziquantel is recommended for treatment of clonorchiasis and opisthorchiasis while triclabendazole is recommended for fascioliasis. Both praziquantel and triclabendazole can be used for paragonimiasis. Individual case-management involves treating people with confirmed or suspected infection, more appropriate where cases are less clustered and health facilities are available. Treatment should be complemented by interventions reducing transmission such as education on safe food practices, improved sanitation and veterinary public health measures. WHO provides forms to request donated praziquantel and application for donated triclabendazole. In July 2018, WHO announced renewed medicine donation to sustain fight against liver infection. See our articles on tropical disease treatment.
5. What is WHO doing to control and prevent foodborne trematode infections?
WHO coordinates multiple activities through its Neglected Tropical Diseases program including promoting prevention and control using a One Health approach, promoting joint implementation with other NTD interventions, supporting countries in their control efforts, and improving data and identifying endemic and high-risk areas. In December 2017, WHO featured how Thailand uses integrated ecosystems health approach to beat cancer-causing disease. In July 2018, WHO reported a review provides fresh perspectives on infection and control. WHO published Taenia solium diagnostic tools report November 2022. The World Health Assembly adopted Resolution WHA31.48 on Prevention and control of zoonoses and foodborne diseases in 1978. For related parasitic diseases, see WHO’s work on taeniasis and cysticercosis, echinococcosis, and rabies. See our articles on global disease control.
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