Clinical Overview of Fasciola

Overview

Fasciola is a liver fluke that can infect the liver and bile duct of exposed people and animals, such as sheep, cattle, goats, and other plant-eating domestic and wild animals.

• Fasciola parasites can cause an infectious disease called fascioliasis. Generally, fascioliasis is more common in people who live or work around livestock (e.g., sheep, cattle, goats) in areas where animal infections are common.

Two Fasciola species can infect people:

• Fasciola hepatica: the main species that infects people. Other names are "the common liver fluke" and "the sheep liver fluke."
• Fasciola gigantica: a related species that primarily affects domestic and wild animals but can also infect people.

Fascioliasis occurs in all continents except Antarctica, in over 70 countries, especially where there are sheep, cattle, or goats.

• In most cases, people can get Fasciola infection by eating raw watercress or other freshwater plants contaminated by larvae.
• People can get infected by consuming contaminated water that they drink. People can also get infected by eating vegetables that they washed or irrigated with contaminated water.
• People cannot get Fasciola from another person.

Cause

Most of the clinical knowledge about fascioliasis is from cases caused by Fasciola hepatica. However, the same principles and clinical features seem to apply to F. gigantica. A person can get Fasciola infection when they consume raw watercress or other freshwater plants contaminated by larvae. A person can also get infected by consuming contaminated water when drinking it or eating vegetables that people washed or irrigated with contaminated water. Under unusual circumstances, people became infected after eating undercooked sheep or goat liver that contained not fully developed forms of the parasite. A person cannot get Fasciola from another person.

At-risk populations

Fascioliasis occurs in more than 70 countries, especially where there are sheep, cattle, or goats.

Fasciola hepatica occurs in all continents except Antarctica. In contrast, Fasciola gigantica only occurs in parts of Africa and Asia.

Although rare, people can become locally infected with Fasciola in the United States. There have been a few reported cases in Hawaii, California, and Florida. Most cases in the U.S. occurred in immigrants that became infected in countries where fascioliasis occurs.

Clinical features

Not all people with Fasciola infection have symptoms.

Both the acute and chronic phases of infection can be symptomatic or symptom free. Nonspecific clinical features of both phases can include the following:

• Fever
• Malaise
• Abdominal pain, in the right upper quadrant, epigastrium, or more diffuse/generalized
• Hepatomegaly
• Abnormal liver tests
• Other abdominal symptoms (such as anorexia, nausea, vomiting, diarrhea, change in bowel habits, and weight loss) and signs (such as hepatomegaly and jaundice)
• Eosinophilia, which is more prominent and less variable during the acute phase than in the chronic phase
• Anemia, especially in children
• Transaminitis (during the chronic phase, laboratory testing also can indicate hepatobiliary obstruction)

Fasciola parasites do not multiply in people. Therefore, the parasite burden, potential for reinfection, and risk for symptomatic disease depends on the inoculum. The large size of the parasite also can be problematic—for example, larval flukes can compound the tissue damage and increase the abdominal pain as they migrate through the liver and can predispose to biliary obstruction during the chronic phase.

The Acute Phase (Acute Fascioliasis)

Other names for the acute phase include the migratory, invasive, hepatic, parenchymal, or larval phase. Immature larval flukes migrate through the intestinal wall, the peritoneal cavity, the liver capsule, and hepatic tissue and, ultimately, to the bile ducts. The acute phase lasts up to approximately 3 - 4 months and ends when the larvae reach and mature in the bile ducts. Larval migration, especially through the liver, can result in tissue destruction, inflammation, local or systemic toxic/allergic reactions, and internal bleeding. Symptoms, in addition to those listed above, can include urticaria, cough, and shortness of breath. This phase can be life threatening in sheep infected with large inocula of parasites. However, severe illness is uncommon in people, although some young children have intense abdominal pain.

The Chronic Phase (Chronic Fascioliasis)

Other names for the chronic phase include the biliary or adult phase. The chronic phase begins when immature larvae reach the bile ducts, mature into adult flukes, and start producing eggs. The eggs pass from the bile ducts into the intestines and then into the feces. During this phase, the patient may be asymptomatic for months, years, or indefinitely. The only finding on routine blood testing might be peripheral eosinophilia, which typically is less prominent than during the acute phase.Some experts differentiate between an asymptomatic latent phase and a symptomatic obstructive phase, which only some patients experience. The symptoms, if any, can be similar to those during the acute phase or can be more focal/discrete, such as clinical manifestations associated with cholangitis and biliary obstruction, which can be intermittent; cholecystitis and gallstones; or pancreatitis (also see below regarding ectopic infection). Fibrosis of the liver may occur.

On the basis of limited data, the life span of adult flukes in people might be five to ten years or even longer (some reports show up to 13.5 years).

Involvement of Ectopic Sites

Fasciola parasites usually go to the liver and bile ducts. However, larval flukes also can migrate to ectopic (aberrant) sites, such as the pancreas, lungs, subcutaneous tissue, genitourinary tract, eyes, or brain. Fasciola parasites at ectopic sites may or may not mature into adult flukes. For example, subadult worms might emerge through the skin.

In addition, in the past, some cases of a syndrome known as Halzoun (a local, Middle Eastern term) (i.e., an acute hypersensitivity reaction involving the buccopharyngeal mucosa and upper respiratory tract in persons who consumed raw or undercooked sheep or goat liver—were attributed to temporary pharyngeal attachment of larval Fasciola flukes. However, it is unclear whether Fasciola spp. versus other parasites or agents can cause this pharyngeal syndrome.

Prevention

People can avoid Fasciola infection by not eating raw watercress and other freshwater plants, especially from areas where livestock feed on land covered by grass (grazing areas) in places where Fasciola infection occurs. It is important to avoid areas with poor sanitation that can have contaminated food and water.

There is no vaccine available to protect people against Fasciola.

Diagnosis

A high index of suspicion is important, especially because the clinical manifestations are nonspecific and the parasitologic tools are suboptimal.

The most widely used diagnostic approach is direct detection of Fasciola eggs, by light-microscopic examination of stool or of duodenal or biliary aspirates. However, egg production typically does not start until approximately 3 - 4 months after the exposure, whereas antibodies to the parasite may become detectable 2 - 4 weeks postexposure. Even during the chronic phase of infection, healthcare providers may need to examine more than one stool specimen to find the parasite, especially in people with light infections.

A cautionary note is that Fasciola eggs can be difficult to distinguish based on morphologic criteria from the eggs of Fasciolopsis buski, which is an intestinal fluke. This distinction has treatment implications. Praziquantel treats infection with Fasciolopsis buski, which typically is not effective therapy for fascioliasis.

False fascioliasis (pseudofascioliasis) refers to the presence of Fasciola eggs in the stool because of recent ingestion of contaminated liver (containing noninfective eggs). Patients can follow a liver-free diet for several days before repeating stool examinations to avoid the potential for misdiagnosis. In addition, serologic testing may be useful to exclude infection.

There are various types of immunodiagnostic tests for Fasciola. CDC provides serologic testing using an immunoblot assay that detects IgG antibody to FhSAP2, a recombinant antigen derived from Fasciola hepatica. As always, healthcare providers should interpret test results in context, with expert consultation. In general, serologic testing can be useful:

• During the acute phase of infection, before the onset of egg production
• During the chronic phase, in cases with low-level or sporadic production of eggs
• In cases of ectopic infection, in which eggs are not in stool.

Other types of testing can provide supportive evidence (such as eosinophilia) or parasitologic confirmation (for example, if imaging or histopathology identify flukes). The following are examples of additional types of testing:

• Routine blood work, including a complete blood count (with a differential white blood cell count) and blood chemistries
• Abdominal imaging, such as ultrasonography, computerized axial tomography (CAT scan), magnetic resonance imaging (MRI scan), and endoscopic retrograde cholangiopancreatography (ERCP)
• Histopathologic examination of a biopsy specimen of liver or other pertinent tissue.

Treatment and recovery

Triclabendazole

Triclabendazole, a benzimidazole compound active against immature and adult Fasciola parasites, is the drug of choice for treatment of fascioliasis. In February 2019, the U.S. Food and Drug Administration (FDA) approved triclabendazole for treatment of fascioliasis in patients at least 6 years of age.

• As with all medications, use of triclabendazole should be individualized.
• There have been documentations of Triclabendazole resistance, particularly in infected animals but also in some infected humans.

Additional Perspective About Therapy

Based on limited data, nitazoxanide might be effective therapy in some patients. Patients take the drug orally, with food. The dosage regimen for adults is 500 mg po bid (twice a day) for seven days. Praziquantel, which is active against most trematodes (flukes), typically is not active against Fasciola parasites and therefore not recommended. In some patients who have biliary tract obstruction, manual extraction of adult flukes (e.g., via endoscopic retrograde cholangiopancreatography [ERCP]) may be indicated.

Care Precautions

Triclabendazole

Treatment in Pregnancy

There are no available data on the use of triclabendazole in pregnant women to inform a drug-associated risk for major birth defects, miscarriage, or adverse maternal or fetal outcomes. See additional perspective in the product label.

Treatment during lactation

According to the product label, there are no data on the presence of triclabendazole in human milk, the effects on the breastfed infant, or the effects on milk production. Published animal data indicate that triclabendazole is detected in goat milk when administered as a single dose to one lactating animal. When a drug is present in animal milk, it is likely that the drug will be present in human milk. The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for triclabendazole and any potential adverse effects on the breastfed infant from the medication or from the underlying maternal condition.

Treatment in pediatric patients

According to the product label, which addresses treatment of fascioliasis, triclabendazole is safe and effective for pediatric patients ages 6 years and older (The FDA has approved the treatment for this age group, but not for younger patients).