Foodborne trematodiases

Key facts

At least 56 million people globally suffer from one or more foodborne trematodiases.

People become infected through the consumption of raw fish, crustaceans or vegetables that harbour the parasite larvae.

Foodborne trematodiases are most prevalent in South-East Asia and South America.

Foodborne trematodiases result in severe liver and lung disease.

Safe and effective medicines are available to prevent and treat foodborne trematodiases.

Foodborne trematodiases affect more than 56 million people throughout the world.

They 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 food: fish, crustaceans and vegetables that harbour the minute larval stages of the parasites (see Table 1).

Transmission

Foodborne trematodiases are zoonoses, i.e. they are naturally transmissible from vertebrate animals to people and vice versa. Direct transmission is however not possible, as the relevant causative parasites become infective only after having completed complex life-cycles that usually involve stages in intermediate, non-human hosts. The first intermediate host is in all cases a freshwater snail, while the second host differs: in clonorchiasis and opisthorchiasis it is a freshwater fish, in paragonimiasis it is a crustacean, while fascioliasis does not require a second intermediate host. The final host is always a mammal.

People become infected when they ingest the second intermediate host that is infected with larval forms of the parasite. In the case of fascioliasis, people become infected when the larvae are ingested together with the aquatic vegetables to which they are attached (see Table 1 for details).