Foodborne trematodiases are caused by trematode worms (“flukes”), among them the species affecting humans with potentially severe outcomes, are Clonorchis, Opisthorchis, Fasciola and Paragonimus.

People become infected through the consumption of raw or undercooked 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.

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 in all cases is a freshwater snail, while the second host differs: for Clonorchis and Opisthorchis it is a freshwater fish, for Paragonimus it is a crustacean, while Fasciola does not require a second intermediate host. The final host is always a mammal.

People get the infection 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).

Table 1. Epidemiological characteristics of foodborne trematodiases

 

Disease Infectious agent Acquired through consumption of Natural final hosts of the infection
Clonorchiasis Clonorchis sinensis Fish Dogs and other fish-eating carnivores
Opisthorchiasis Opisthorchis viverrini,
O. felineus
Fish Cats and other fish-eating carnivores
Fascioliasis Fasciola hepatica,
F. gigantica
Aquatic vegetables Sheep, cattle and other herbivores
Paragonimiasis Paragonimus spp. Crustaceans (crabs and crayfish) Cats, dogs and other crustacean-eating carnivores

culled: http://www.who.int/mediacentre/factsheets/fs368/en/

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