Your Guide to
Neglected Tropical Diseases

Foodborne trematodiases are a group of parasitic worm infections caused by several types of flatworms called flukes. These parasites have complex life cycles involving multiple hosts and infect humans through contaminated food. Early infections often go unnoticed as they cause few or no symptoms. However, chronic infections lead to severe liver or lung disease. Some flukes lodge in the bile ducts of the liver, causing inflammation, scarring, and, in some cases, bile duct cancer. Other types cause blockages, severe abdominal pain, jaundice, and liver cirrhosis. Lung flukes settle in lung tissue, causing chronic cough, bloody sputum, and chest pain that can persist for years.

People become infected by eating raw or undercooked freshwater fish, crustaceans, and vegetables that contain parasite larvae. The infection cannot spread directly from person to person or directly from animals to people. Instead, the parasites must complete a complex life cycle through intermediate hosts in freshwater environments. All flukes first develop in freshwater snails, then move to a second host where they wait to infect humans. Different types of flukes use different second hosts: some use freshwater fish, others use crustaceans like crabs and crayfish, and still others contaminate freshwater plants. Transmission patterns vary by parasite species and reflect the natural settings of intermediate hosts, local eating habits, food preparation methods, and the local culture. The rapid expansion of fish farming has increased risk in many areas.

Foodborne Trematodes Infections (Lung fluke life cycle)

This visual shows how Paragonimus (lung fluke) spreads. Other foodborne trematodes follow a similar cycle. The key difference is what people eat to become infected: freshwater fish for liver flukes, and aquatic plants for Fasciola.

Geographic scope:

• Cases have been reported in over 70 countries worldwide.
• East and Southeast Asia and South America are the most severely affected regions.
• In some highly endemic villages in Laos, infection with the liver fluke has been found in up to roughly 80-90% of people tested.

Population affected:

• An estimated 44 million people were infected globally as of 2021, though the true burden is likely higher due to significant underreporting.

Safe and effective medications are available. Two main drugs are used depending on the type of fluke: praziquantel and triclabendazole. Both are generally safe with mild side effects. WHO helps provide these medications free of charge to endemic countries. In areas with many infected people, entire communities may receive mass drug administration (MDA). In other low-prevalence areas, only those confirmed or suspected to be infected receive treatment.

Preventing infection requires multiple complementary approaches. Thorough cooking of freshwater fish, crustaceans, and vegetables kills the parasite larvae and is the most important individual protective measure. Community awareness-raising activities, clean water, improved sanitation, and treating infected livestock address transmission at a broader level. Geography matters, too. People living near freshwater bodies face more than double the infection risk of those living farther away, making targeted interventions in these communities especially important.