Opisthorchis

Opisthorchis species are liver fluke parasites that humans can get by eating raw or undercooked fish, crabs, or crayfish from areas in Asia and Europe where the parasite is found, including Thailand, Laos, Cambodia, Vietnam, Germany, Italy, Belarus, Russia, Kazakhstan, and Ukraine.

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Opisthorchis felineus Korea

Liver flukes infect the liver, gallbladder, and bile duct in humans. While most infected persons do not show any symptoms, infections that last a long time can result in severe symptoms and serious illness. Untreated, infections may persist for up to 25–30 years, the lifespan of the parasite. Typical symptoms include indigestion, abdominal pain, diarrhea, or constipation. In severe cases, abdominal pain, nausea, and diarrhea can occur. O. felineus, in addition to presenting with the typical symptoms also seen in O. viverrini infections, can present with fever, facial swelling, swollen lymph glands, sore joints, and rash—similar to the signs and symptoms of schistosomiasis. Chronic O. felineus infections may also involve the pancreatic ducts.Diagnosis of Opisthorchis infection is based on microscopic identification of parasite eggs in stool specimens. Safe and effective medication is available to treat Opisthorchis infections. Adequately freezing or cooking fish will kill the parasite

Epidemiology & Risk Factors

Opisthorchis species are liver fluke parasites (trematodes or worms). Opisthorchis viverrini is known as the Southeast Asian liver fluke and O. felineus is known as the cat liver fluke.

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Opisthorchis Life Cycle

Liver fluke infections occur mostly in people living in some areas where the parasites are found. O. viverrini is found mainly in northeast Thailand, Laos, Cambodia, and central and southern Vietnam. O. felineus is found mainly in Italy, Germany, Belarus, Russia, Kazakhstan, and Ukraine. Travelers to Asia or Europe who consume raw or undercooked fish are at risk for liver fluke infection.

People become infected by eating raw or undercooked freshwater fish containing the larvae. Lightly salted, smoked, or pickled fish may contain infectious parasites. Drinking river water or other nonpotable water will not lead to infection with Opisthorchis.

Causal Agent

Trematodes (flukes) Opisthorchis viverrini (Southeast Asian liver fluke) and Opisthorchis felineus (cat liver fluke).

Life Cycle

The adult flukes deposit fully developed eggs that are passed in the feces. After ingestion by a suitable snail (first intermediate host) , the eggs release miracidia , which undergo in the snail several developmental stages (sporocysts , rediae , cercariae ). Cercariae are released from the snail and penetrate freshwater fish (second intermediate host), encysting as metacercariae in the muscles or under the scales. The mammalian definitive host (cats, dogs, and various fish-eating mammals including humans) become infected by ingesting undercooked fish containing metacercariae. After ingestion, the metacercariae excyst in the duodenum and ascend through the ampulla of Vater into the biliary ducts, where they attach and develop into adults, which lay eggs after 3 to 4 weeks. The adult flukes (O. viverrini: 5 mm to 10 mm by 1 mm to 2 mm; O. felineus: 7 mm to 12 mm by 2 mm to 3 mm) reside in the biliary and pancreatic ducts of the mammalian host, where they attach to the mucosa.

Opisthorchis viverrini

Disease

Liver flukes infect the liver, gallbladder, and bile duct in humans. While most infected persons have no symptoms, infections that last a long time can result in severe symptoms and serious illness. Infections are not known to last longer than 25–30 years, the life span of the parasite.

People become infected by eating raw or undercooked freshwater fish containing the larvae. Lightly salted, smoked, or pickled fish may contain infectious parasites. Drinking river water or other nonpotable water will not lead to infection with Opisthorchis.

The eggs of Opisthorchis viverrini are ingested by snails in fresh water. After the eggs hatch, infected snails will release microscopic larvae that can enter freshwater fish. People become infected when eating raw or undercooked fish that contains the parasite. After ingestion, the liver flukes grow to adult worms that live inside the human bile duct system. The life cycle takes three months to complete in humans. Infected people will then pass eggs in their stool or may cough them up.

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Incidence of CCA and O. viverrini in Thailand

Diagnosis

Ova and parasite (O&P) stool examinations for liver fluke eggs is the only available way to diagnosis Opisthorchis infection. More than one stool sample may be needed to identify the eggs. The eggs of Opisthorchis are very similar to those of Clonorchis, another liver fluke, but can be distinguished by microscopic features. Stool examination is unlikely to result in a diagnosis in persons whose only exposure to Opisthorchis took place more than 25–30 years ago (the life span of a liver fluke), as the liver fluke must be alive in order to produce eggs. Additionally, cysts containing the parasite can sometimes be detected by ultrasound, CT, or MRI. Testing the blood for Opisthorichis is not useful for patient management and no blood test to detect infection is available in the United States. In the absence of detection of liver flukes, there is no test available that can determine if liver fluke infection is the underlying cause of cholangiocarcinoma or other liver, bile duct, or gallbladder conditions.

Treatment

[[Praziquantel[[ or albendazole are the drugs of choice to treat Opisthorchis infection.

Prevention & Control

Do not eat raw or undercooked freshwater fish. Lightly salted, smoked, or pickled fish can contain infectious parasites. Drinking river water or other nonpotable water will not lead to infection with Opisthorchis.

The FDA recommends the following for fish preparation or storage to kill any parasites.

Cooking

• Cook fish adequately (to an internal temperature of at least 145° F [~63° C]).

Freezing (Fish)

• At -4°F (-20°C) or below for at least 7 days (total time); or
• At -31°F (-35°C) or below until solid, and storing at -31°F (-35°C) or below for at least 15 hours; or
• At -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for at least 24 hours.

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