Foodborne trematodiases are caused by trematode worms (“flukes”), of which the most common species affecting humans are Clonorchis, Opisthorchis, Fasciola and Paragonimus. People become infected through the consumption of raw or poorly cooked freshwater fish (clonorchiasis and opisthorchiasis), crustaceans (fascioliasis) and vegetables (paragonimiasis) that harbour the minute larval stages of the parasites.
In people with clonorchiasis and opisthorchiasis, the adult worms lodge in the smaller bile ducts of the liver, causing inflammation and fibrosis of the adjacent tissues and eventually cholangiocarcinoma, a severe and fatal form of bile duct cancer. In people with fascioliasis, the adult worms lodge in the larger bile ducts and the gall bladder, where they cause inflammation, fibrosis, blockage, colic pain and jaundice. Liver fibrosis and anaemia are also frequent. In people with paragonimiasis, the final location of the worms is the lung tissue, causing symptoms that can be confounded with tuberculosis such as chronic cough with bloodstained sputum, chest pain, dyspnoea (shortness of breath) and fever. Migration of the worms is possible: cerebral locations are the most severe.
Several countries in the Western Pacific Region have reported cases of foodborne trematodisasis:
- Clonorchiasis – China, Japan, Republic of Korea and Philippines
- Opisthorchiasis – Cambodia, Lao People’s Democratic Republic, Philippines and Viet Nam
- Fascioliasis – Australia, China, Japan, Republic of Korea, Malaysia and Philippines
- Paragonimiasis – Australia, China, Japan, Republic of Korea, Malaysia, Papua New Guinea and Philippines