Foodborne trematode infections
Foodborne trematode infections, or foodborne trematodiases, are a group of parasitic infections caused by trematodes (flatworms or “flukes”) that are acquired through ingestion of food contaminated with the larval stages of the parasite.
Transmission is linked to human behaviour patterns related to methods of producing, processing and preparing foods. In particular, dishes containing raw fish, crustaceans and plants are an established dietary tradition of many populations living in countries where these diseases are endemic. Foodborne trematodiases are thus sustained and perpetuated by entrenched cultural practices.
Foodborne trematode infections are all zoonotic infections; that is, diseases primarily affecting domestic or wild animals that may be transmitted to humans. Transmission occurs when humans enter the parasite’s biological cycle to replace its natural reservoir final animal host. Transmission cycles differ for each type of parasite, but they share some common characteristics: they are complex and involve one or two intermediate hosts, usually a mollusc and an animal species such as fish or crustaceans.
A significant number of trematode infections are transmitted by consuming contaminated food. Although most of these infections are only mildly pathogenic, severe pathology in humans is caused by four main genera: Clonorchis spp. (that cause clonorchiasis); Opisthorchis spp. (that cause opisthorchiasis); Fasciola spp. (that cause fascioliasis); and Paragonimus spp. (that cause paragonimiasis).
Foodborne trematode infections are particularly prevalent in east and south-east Asia, and in central and south America. The number of individuals affected is difficult to calculate; WHO estimates that at least 40 million people are infected.