Opisthorchiasis is a parasitic infection caused by liver flukes of the genus *Opisthorchis*, primarily *Opisthorchis viverrini* and *Opisthorchis felineus*. These parasites inhabit the bile ducts of the liver after humans consume raw or undercooked freshwater fish containing the infective larvae. The symptoms of opisthorchiasis can vary widely depending on the stage of infection, the parasite load, and the duration of the disease.
In the early or acute phase, which occurs weeks to months after infection, many people may experience mild or nonspecific symptoms, or even remain asymptomatic if the parasite burden is low. When symptoms do appear, they often include fever and abdominal discomfort, particularly pain in the right upper quadrant of the abdomen where the liver is located. This pain can be dull or sharp and may be accompanied by a feeling of fullness or discomfort after eating. The liver itself may become enlarged (hepatomegaly), which can be detected by physical examination. Alongside these symptoms, there is often an increase in eosinophils, a type of white blood cell that responds to parasitic infections, leading to marked eosinophilia in blood tests. Liver function tests may show abnormalities, reflecting inflammation or damage to the liver and bile ducts.
As the infection progresses into the chronic phase, symptoms can become more pronounced and complicated. Chronic opisthorchiasis often leads to persistent inflammation and fibrosis of the bile ducts. Patients may experience recurrent episodes of abdominal pain, jaundice (yellowing of the skin and eyes), and digestive disturbances such as nausea, vomiting, and diarrhea. The bile ducts may become obstructed, causing cholangitis, an infection of the bile ducts, which presents with fever, chills, and worsening abdominal pain. Over time, chronic inflammation can lead to serious complications including the development of gallstones and an increased risk of cholangiocarcinoma, a type of bile duct cancer.
Other symptoms that may be observed include fatigue and weight loss, which are common in chronic parasitic infections due to ongoing inflammation and impaired liver function. Some patients might also develop signs of liver cirrhosis if the infection is longstanding and severe. In rare cases, the parasites can cause pancreatitis if they migrate to or block the pancreatic ducts, leading to upper abdominal pain radiating to the back, nausea, and vomiting.
Because the symptoms of opisthorchiasis overlap with many other liver and gastrointestinal diseases, diagnosis often requires a combination of clinical suspicion, laboratory tests showing eosinophilia and liver enzyme abnormalities, and confirmation by detecting parasite eggs in stool samples or using imaging techniques to visualize bile duct changes.
In summary, the symptoms of opisthorchiasis range from mild or absent in early infection to severe liver and bile duct disease in chronic cases. Key symptoms include right upper abdominal pain, fever, hepatomegaly, jaundice, digestive upset, and signs of bile duct obstruction or inflammation. The disease can silently progress to serious complications if untreated.
