Foodborne trematodiases

Foodborne trematode (FBT) infections, taeniasis and cysticercosis are noteworthy neglected tropical diseases caused by trematodes (flatworms or “flukes”) or pork tapeworms. People become infected through the consumption of raw or poorly cooked freshwater fish, crustaceans and vegetables hat harbour the parasite larvae. Early and light infections often pass unnoticed, as they are asymptomatic or only scarcely symptomatic. Conversely, if the worm load is high, general malaise is common and severe pain can occur, especially in the abdominal region. Chronic infections are invariably associated with severe morbidity. Foodborne trematodiases result in severe liver and lung disease.

Two species of FBTs (liver flukes) are confined to Asia. In some hyperendemic villages in Lao PDR, a record 80% prevalence of one species (O. viverrine) have been recorded. Eating raw fish and contaminated freshwater plants is a possible behavioural cause. WHO supports endemic countries in the WPR in conducting disease mapping, donation of Praziquantel for treatment and MDAs, and building capacity to diagnose, treat, and prevent cases of these Zoonotic diseases.

Transmission of these trematodes is closely linked with food habits and hygiene in endemic areas. Therefore, food safety risk communications play a key role for the prevention of reinfection. As they are also zoonotic, veterinary public health and environmental measures, including treating domestic or livestock animals, enforcing separation between husbandry and humans, and draining grazing lands, might also be adopted.

The public health burden due to foodborne trematodiases is predominantly due to morbidity rather than mortality with early and light infections often going unnoticed. Chronic infections are associated with severe morbidity with symptoms reflecting the organ in which the adult worms are located in.

Clonorchis and Opisthorchis species have adult flukes that lodge in the smaller bile ducts of the liver, resulting in inflammation and fibrosis of surrounding tissues. Acute or early infection may result in non-specific gastrointestinal symptoms. Chronic infection can result in cholangiocarcinoma, a fatal bile duct cancer. Both C. sinensis and O. viverrini are classified as carcinogens.

Fasciola adult worms lodge in larger bile ducts and gall bladder resulting in inflammation, fibrosis, blockage, colic pain, and jaundice. Chronic infection can result in liver cirrhosis.

The final location of Paragonimus species is in the lung tissue, resulting in a chronic cough, blood-stained sputum, chest pain, dyspnoea (shortness of breath), and fever. These symptoms can be confounded with tuberculosis. Adult worms may also infect extra-pulmonary locations such as the brain and can result in symptoms of headaches, mental confusion, convulsions, and cerebral hemorrhage.

Treatment of foodborne trematodiases is important to prevent progression of clinical disease and reduce associated morbidity. Treatment can be offered through preventive chemotherapy or individual case management.

Preventive chemotherapy involves a population-based approach where everyone in a given region or area is given medicines, irrespective of their infection status. This is recommended in areas where large numbers of people are infected. Praziquantel is recommended for the treatment of clonorchiasis and opisthorchiasis while triclabendazole is recommended for fascioliasis. Both praziquantel and triclabendazole can be used for the treatment of paragonimiasis.

Individual case-management involves the treatment of people with confirmed or suspected infection. This approach is more appropriate where cases are less clustered and where health facilities are available.

Treatment should be complemented by interventions that reduce transmission such as education on safe food practices, improved sanitation, and veterinary public health measures.