NTDs: Foodborne trematodiases – the pitfalls of accidentally eating parasitic worms

This post is the 7th in a series highlighting the WHO’s list of 17 Neglected Tropical Diseases (now technically 18 as mycetoma was added to the list at the 69th World Health Assembly in May 2016). To read the previous posts in this series click here.

An adult fasciola worm measuring 4.5cm. They can reach 7cm. Courtesy Dr. Albis Gabrielli/WHO.

The term “foodborne trematodiases” encompasses a group of parasitic infections caused by trematodes (flatworms or “flukes”), which humans accidentally ingest through consumption of food contaminated by the larval stage of the parasites. On the bright side, because there is always a bright side if you look hard enough, foodborne trematode infections are all zoonotic infections, meaning humans are accidental hosts and the parasites normally live in animals.

While foodborne trematodiases encompass many different infections, there are four main parasite genera that cause the most problems in humans. These genera are Clonorchis spp., Opisthorchis spp., Fasciola spp., and Paragonimus spp..  These trematodes infect around 56 million people in 70 countries around the world, especially in east and south-east Asia, and in central and South America. Infections result in severe liver and lung damage.

Not all food gets contaminated with the trematodes, however, it’s mainly raw fish, crustaceans, and leafy vegetables. This is why the areas in East Asia and South America are hit so hard; fishing is a substantial part of their economy and subsequently their diet.

Foodborne trematodiases

Courtesy WHO.

But have no fear, there are drugs that exist to help prevent and cure each of the four main diseases. Prevention drugs are offered to folks on the population-level when the burden of disease is high, regardless of whether a person is infected or not. Individual case management is offered to folks on the individual level, for folks who have a suspected or confirmed case, and is used when cases are less widespread and when health facilities exist to help manage the case. The WHO has negotiated a deal with Novartis Pharma AG whereby the company donates the medication for fascioliasis and paragonimiasis, which are shipped free of charge to ministries of health that request them. This deal has resulted in 2.1 million doses provided since 2007. In 2015, about 600,000 people were treated for all of the various foodborne trematodiases worldwide.

Moral of the story, try not to eat raw fish so you don’t end up with a trematode hitching a ride in your body. But if you do end up with such a troublesome guest, treatment is possible.

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