Neglected tropical diseases: Clonorchiasis

Poverty, the tradition to eat raw or undercooked freshwater fish, and inadequate sanitation in rural areas drive high infection rates. Limited healthcare access delays diagnosis, perpetuating cycles of contamination through untreated human waste in water systems.

Warmer temperatures and flooding can expand habitats for snails and fish that carry the parasite, increasing the chances of infection. Climate change may also affect food availability, leading some communities to fish in contaminated areas where infected fish are more common. This raises the risk of people catching and eating fish that carry the parasite.

Migrants or travellers from endemic regions may carry asymptomatic infections. Doctors in non-endemic areas often lack awareness, and stool tests for parasite eggs are not routine unless specifically requested.

Yes. Dogs, cats, and pigs can act as reservoir hosts, shedding parasite eggs in their feces, which might contaminate water. This sustains the lifecycle, emphasizing the need for veterinary action in endemic regions.

No. The parasite requires specific snail and fish hosts to complete its lifecycle. However, cross-contamination of utensils may pose risks for other foodborne illnesses, highlighting the need for kitchen hygiene.

Traditional dishes like koi pla (Thailand) or sashimi (Japan) are an important part of local culture and identity, making change difficult. However, eating raw fish can lead to infections like clonorchiasis. To reduce the risk without disrespecting traditions, education campaigns can promote cooking fish thoroughly as a safer alternative. Cooking is a practical solution in many communities where freezing fish may not be possible.

Yes. Long-term clonorchiasis infection causes chronic inflammation and damage to the bile ducts, which can lead to serious liver problems. One of the most severe outcomes is cholangiocarcinoma, a deadly bile duct cancer. The parasite's presence in the bile ducts triggers continuous irritation and scarring, which over time increases the risk of cancer developing. People with chronic clonorchiasis are also more vulnerable to other liver diseases, such as hepatitis B or C, especially when combined with other factors like alcohol use.

Children often experience malnutrition and stunted growth due to chronic infection. Early exposure increases lifetime bile duct cancer risk, as damage accumulates over decades.

Clonorchiasis is usually treated with a medicine called praziquantel, which kills the adult worms living in the bile ducts. Treatment can help stop the infection and reduce symptoms. However, it cannot undo the long-term damage to the liver and bile ducts caused by chronic infection. This is why preventing infection—by not eating raw or undercooked freshwater fish—is very important.

The best way to prevent clonorchiasis is to avoid eating raw or undercooked freshwater fish. Cooking fish thoroughly until it is fully cooked kills the parasites. Improved sanitation is essential to prevent contamination with human feces of water sources where fish live. Where possible, community-based approaches like fish farming in clean water and public education campaigns about the risks of eating raw fish also help reduce infection rates.