Summer is the time of year when public health messaging reminds us of foodborne infections from bacteria like Salmonella, E.coli and Listeria. While these are some of the most widespread foodborne infections, particularly in the United States, it is critical to remember there are many more species beyond the bacteria that cause illness in our food and water supply. Amongst them is a class of neglected tropical diseases known as foodborne trematode infections. Foodborne trematodiasis is group of NTDs that includes four infections: clonorchiasis, opisthorchiasis, fascioliasis and paragonimiasis—all of which are parasitic flatworms, or flukes, which cause severe disease globally.
The first two in the group, clonorchiasis, caused by the parasitic worm Clonorchis sinensis, and opisthorchiasis, caused by two different flukes, Opisthorchis viverrini or O. felineus, cause disease through the consumption of fish (1). The natural final hosts of infection for clonorchiasis and opisthorchiasis are dogs and cats, respectively, as well as other fish-eating carnivores (1). Fascioliasis, caused by Fasciola hepatica and F. gigantica, is acquired through the consumption of aquatic vegetables, making sheep, cattle and other herbivores the natural final hosts of infection (1). Finally, paragonimiasis, caused by Paragonimus fluke, is contracted through the consumption of crustaceans, including crabs and crayfish (1). Cats, dogs and crustacean-eating carnivores are the natural final hosts of infection (1). It is important to note that while humans are not the natural final hosts of the four flukes, there are approximately 200,000 human infections and 7,000 human deaths per year worldwide due to the trematodes, resulting in more than two million healthy years of life lost (1).
The global impact of each disease varies. Clonorchiasis and opisthorchiasis are only found Asia, while paragonimiasis is found in Africa; fascioliasis, however, is found globally (1). While the presence of the infections is widespread, with most cases are reported in Asia and South America (1). If contracted, the prescription medications Praziquantel and Triclabendazole are available to treat foodborne trematode infections (1,2).
The lifecycle of the trematodes relies on the interrelationship of humans, animals and the environment. Larvae in freshwater enter aquatic snails as an intermediate host, where they grow and subsequently are released when they are developed enough to be free-swimming (3). As they further develop, they invade fish, crustaceans and aquatic vegetables, where they are able to be transmitted to humans or animals who eat raw or undercooked freshwater species (3). Poor waste practices, leading to infected feces entering the water as waste or fertilizers, propels the cycle of trematode infections through the interaction of humans and animals with the environment (3).
Beyond the burden of disease on humans, the economic loss in endemic regions from livestock deaths is significant. Furthering the cycle of poverty, when people’s livelihood depends on being able to raise and sell livestock, losing their commodities to parasitic disease threatens their financial survival and pushes them further into poverty. Therefore, control and prevention methods utilize an approach focusing on the relationship between humans, animals and the environment. Education on proper food preparation is a critical piece for preventing transmission to humans because raw and undercooked meats are a main mechanism of transmission of the parasites. Identifying clean water sources and making hygienic food storage practices accessible help address the human and animal components of foodborne trematode infections. Current practices focus on the treatment and prevention of disease in animals and humans, with the hope that in the future, once hygienic practices are established, the control and prevention of trematodes in the environment can be addressed.