What are the other Names for this Condition? (Also known as/Synonyms)

• Cat Liver Fluke Disease
• Opisthorchis Felineus Infection
• Southeast Asian Liver Fluke Disease

What is Opisthorchiasis? (Definition/Background Information)

• Opisthorchiasis is an infection caused by either of the two parasite worms, the cat liver fluke, or scientifically called Opisthorchis felineus  (also known as Opisthorchis tenuicollis), or the Southeast Asian liver fluke (called as Opisthorchis viverrini). The term “fluke” means flatfish, since these parasites are flat
• The parasite has various stages (life cycle), before it develops into a fully-grown worm
  • At the very early stage, it moves from water (environment) into the body of a mollusk, such as a snail. Following this, it leaves the mollusk body and enters into a freshwater fish, such as a smelt
  • Humans ingest the parasite when they eat the raw, partially-cooked, salted, or under-processed fish. More commonly, dogs, cats, pigs, and rats eat the freshwater fish and easily ingest the parasite
  • Once in the body of humans, it resides and grows into an adult worm, measuring up to 1.5 cm in size in the liver bile ducts
  • The adult worm lays and hatches its eggs, which gets passed into the intestine from the bile duct and come out through stool, into the environment. In this manner, the life-cycle of the parasite continues
  • The parasitic worm can live in the bile duct or the liver for 20-30 years         
• Opisthorchis felineus (cat liver fluke) is commonly found in Eastern Europe and Russia; whereas, Opisthorchis viverrini (Southeast Asian liver fluke) is commonly found in Thailand and Laos. Opisthorchiasis is generally known as Cat Liver Fluke Disease, if it is caused by O. felineus, and it is known as Southeast Asian Liver Fluke Disease, if it is caused by O. viverrini
• In humans, the acute infectious stage is usually asymptomatic. In chronic infections, bile duct and liver abnormalities, such as abdominal pain (especially on the right side near the rib cage), are common. It may also cause inflammation of the liver
• If chronic infection is left untreated, it may lead to bile duct cancer (cholangiocarcinoma)

Who gets Opisthorchiasis? (Age and Sex Distribution)

• Any individual consuming raw, uncooked, or unprocessed freshwater fish in the endemic regions, where the parasite is prevalent, is at risk for Opisthorchiasis. Very rarely do children get infected with Opisthorchiasis
• Individuals of any race or ethnicity may be affected. People, who consume imported, undercooked, or pickled freshwater fish, containing the parasitic cysts of Opisthorchis species, are likely to be infected
• The Cat Liver Fluke Disease is generally observed in people living in Eastern Europe and Russia, while the Southeast Asian Liver Fluke Disease infects the people of Thailand, Cambodia, Vietnam and Laos. It is believed that half the population of Thailand has Opisthorchiasis. In non-endemic areas such as the US, it is more common among Asian immigrants

What are the Risk Factors for Opisthorchiasis? (Predisposing Factors)

The risk factors of Opisthorchiasis include:

• People who eat freshwater fish that is raw, undercooked, pickled, or unprocessed (even if imported), containing the parasitic worms are at a high risk of contracting Opisthorchiasis.
• Living near freshwater water bodies, such as rivers, ponds, or lakes, in the endemic regions of Eastern Europe, Russia, Thailand or Laos where these parasites are highly prevalent and consuming raw fish

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Opisthorchiasis? (Etiology)

The causes of Opisthorchiasis include:

• Opisthorchiasis is a foodborne infection caused by the cat liver fluke or the Southeast Asian liver fluke, a parasitic worm which grows and resides in the bile ducts of the liver in humans and fish-eating mammals. It is acquired by eating freshwater fish containing the fluke larvae
• The eggs of Opisthorchis are taken in by snails that live in the freshwaters. These eggs hatch and the infected snails release microscopic larvae that enter freshwater fish (which serves as an intermediate host). Humans (or mammals), who are the final hosts, are infected when they eat raw or undercooked fish containing the cysts
• On entering the human body, the cyst travels to the intestine and then moves to the liver and resides in the bile ducts, where they grow into adult worms. The adult worm lays and hatches eggs that is passed on to the intestine and then into the feces
• Opisthorchis felineus is usually a parasite of cats, dogs, pigs, and whales, while Opisthorchis viverrini is commonly found in dogs and cats

What are the Signs and Symptoms of Opisthorchiasis?

Most individuals infected with Opisthorchiasis do not present any symptoms. Individuals infected for a long time (chronic) may get serious illness. A long-standing inflammation or re-infection of the bile ducts could lead to scarring of the bile duct, and inflammation of the liver.

• The signs and symptoms of Opisthorchiasis may include:
• Abdominal pain, nausea, and diarrhea
• Any pathology (infection) of the bile duct and adjacent organs can cause abdominal pain (particularly under the rib cage to the right), jaundice, fever, or chills
• Biliary stone formation (cholelithiasis): Inflammation and scarring of the bile ducts leads to stasis (decreased flow) of bile, which may to lead to the formation of stones
• Due to bile stones and narrowing changes, the affected individuals may get the following:
  • Jaundice
  • Intermittent biliary duct obstruction can cause abdominal pain (biliary colic)
  • Cholangitis - infection and inflammation of the bile duct
  • Cholecystitis - infection and inflammation of the gall bladder        
• Pancreatitis (inflammation of the pancreas) due to obstruction of the tube (duct) that is common to the liver bile duct and pancreas

How is Opisthorchiasis Diagnosed?

The following tests and procedures may be used to diagnose Opisthorchiasis:

• Thorough evaluation of the individual’s medical history and a complete physical examination, especially of the abdomen
• During history taking the physician may want to know the following:
  • When the symptoms began and whether they are becoming worse

  • Information on dietary habits (especially raw fish consumption), travel history, and places of residence             

• The diagnosis of Opisthorchiasis or clonorchiasis (a similar condition) is suspected when the individual is accustomed to consuming raw fish and has signs and symptoms pertaining to the right side of the abdomen
• Consultation with a gastroenterologist and or infectious disease specialist may be necessary
• Blood tests:
  • Complete blood count may show eosinophilia - increased levels of white blood cell eosinophils in the peripheral blood. It is usually seen with parasitic infections
  • Tests for checking antibody levels for the parasite             
• Examination of a stool sample may be undertaken to detect the presence of the eggs of Opisthorchis to confirm diagnosis
• Imaging tests may be performed to look for disease activity in the bile duct, liver, gallbladder, or pancreatic duct
  • Ultrasound, CT, or MRI scans of the liver, gallbladder, biliary and pancreatic ducts  may be taken
  • Endoscopic retrograde cholangiopancreatography (ERCP) may be done to check for abnormalities in the biliary and pancreatic ducts

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Opisthorchiasis?

The complications of Opisthorchiasis could include:

• Scarring of the bile duct or gallstone formation that could lead to diseases such as
  • Cholecystitis (infection of the gallbladder)
  • Cholangitis (infection of the biliary duct)         
• Hepatitis (inflammation of the liver)
• Cholangiocarcinoma - cancerous growth in one of the duct that carries bile from the liver to the small intestines

Researchers believe that O. viverrini (Southeast Asian liver fluke) can cause cholangiocarcinoma, especially in the presence of dietary nitrosamines (which is used as a preservative).

How is Opisthorchiasis Treated?

The treatment options of Opisthorchiasis include:

• The World Health Organization (WHO) recommends anti-worm medication praziquantel for infected individuals. Praziquantel may be given to individuals as a preventative measure; to individuals who have no signs of the disease, but live in the endemic regions
• Surgery may be required, if obstruction of the bile duct persists, despite treatment with praziquantel to remove the worms and/or stones
• Treatment of complications as required with intravenous antibiotics and through surgical intervention

How can Opisthorchiasis be Prevented?

The preventative measures of Opisthorchiasis include:

• Educating the community is the most important and effective tool in preventing Opisthorchiasis
• Avoidance of raw or undercooked freshwater fish consumption. However, it has been observed that some individuals do not stop the habit, despite understanding the consequences
• Clonorchiasis can be prevented by freezing fish (Centers for Disease Control and Prevention recommendation) using one of the strategies:
  • At -4⁰F or below for 7 days
  • At -31⁰F or below until solid and then storing at -31⁰F or below for 15 hours
  • At -31⁰F or below until solid and then storing at -4⁰F or below for 24 hours       
• Cooking fish adequately to an internal temperature of at least 145⁰ F
• Reducing the use of night soil, a fertilizer contaminated with human feces, which is used in some places to fertilize fish ponds to increase fish production. This practice must be strictly eliminated to prevent Opisthorchiasis

What is the Prognosis of Opisthorchiasis? (Outcomes/Resolutions)

A proper and timely diagnosis and treatment can lead to a good prognosis. Early diagnosis may prevent long-term complications of Opisthorchiasis such as cholangiocarcinoma.

Additional and Relevant Useful Information for Opisthorchiasis:

• Opisthorchiasis has been reported in the US among some immigrant population. Suspicion for Opisthorchiasis should be high in immigrants from Asia, who present with bile duct disorders
• Clonorchiasis is another disease, in which the parasite has a similar life-cycle and clinical presentation. Clonorchiasis infection is common in Korea, China, Taiwan, Vietnam, Japan, and eastern Russia