Fascioliasis is a rare, infectious, zoonotic (infectious disease that is passed from animals to humans or vice versa), a parasitic disease that is mainly caused by consuming raw freshwater plants such as watercress that are contaminated with infective Fasciola hepatica larvae (metacercariae), these are flatworms found in all continents except Antarctica. It mainly affects the liver and bile ducts in humans as well as in animals like sheep and cattle. Although fascioliasis affects people, it is more common among livestock, especially cattle and sheep. Fascioliasis is both treatable and preventable.
Fasciola hepatica (F. hepatica) is often referred to as ‘’the common liver fluke’’ or ‘’sheep liver fluke’’ because it mainly affects the liver of people who accidentally ingest raw watercress or freshwater plants contaminated by sheep or cattle dung.
Causes of fascioliasis
Fascioliasis is mainly caused by the ingestion of raw watercress or other freshwater plants that are contaminated with immature parasitic larvae (young worms) found within sheep or cattle dung. However, people can also become infected by drinking contaminated water or eating raw vegetables washed with contaminated water.
How is fascioliasis transmitted?
- Final host
- Intermediate host
- Infected livestock, especially cattle and sheep (host) ingest freshwater plants such as watercress that are contaminated with immature parasitic larvae
- The immature parasitic larvae move through the intestinal wall, abdominal cavity and liver tissue before entering the bile ducts, where they develop into mature adult worms
- The adult worms lay eggs that are passed from the bile ducts into the small intestine
- The eggs then become embryonated and hatch into free-swimming larvae (‘’miracidia’’) that swim and bore themselves directly into a freshwater snail (intermediate host)
- Within the snail, the miracidia go through multiple complex developmental stages until they become “cercariae’’.The cercariae are then released into the water, where they swim and attach themselves to the stems and leaves of freshwater plants such as watercress, forming ‘’metacercariae’’ (infective F. hepatica larvae). At this stage, the freshwater plants become carriers of the parasitic infection, and if ingested by humans (definitive or final hosts), lead to fascioliasis
Signs and symptoms of fascioliasis
The signs and symptoms of fascioliasis vary, depending on which phase of the infection the person is experiencing
The phases of fascioliasis infection include:
- Incubation phase: This phase lasts for a couple of days to months and occurs directly after the person ingests larvae with contaminated food or water. It is generally asymptomatic (you will experience no symptoms)
- Acute phase: This phase lasts for 2-4 months and occurs when the immature parasitic larvae eat their way into the liver tissue and migrate into the bile ducts, causing heavy internal bleeding. You will start experience symptoms like nausea, fever, hepatomegaly (swelling and enlargement of the liver), skin rashes and extreme abdominal pain
- Chronic phase: This phase begins months to years after the mature adult worms release their eggs from the bile ducts and small intestine into the stools (faeces). You will start developing symptoms like jaundice (yellowing of the eyes), anaemia (low red blood cells or haemoglobin), liver fibrosis (hardening and scarring of the liver), pancreatitis (inflammation of the pancreas), gallstones (hard pebble-like structures found within the gallbladder), and intermittent pain (stabbing, shotting, stinging pain that comes and goes)
Diagnosis of fascioliasis
To diagnose fascioliasis, your healthcare provider will check the following:
- F. hepatica eggs in the stools: Multiple stool samples are often required to be thoroughly examined under a microscope to identify the parasite
- An anamnestic (immune) response to the parasites: This is usually confirmed by finding a high level of worm-specific antibodies (foreign proteins that activate the immune system of the human host) or worm-specific antigens (foreign substances that human antibodies target and ‘attack’) in immunological blood tests
- Eosinophilia: Eosinophils are a specific type of white blood cells that fight against infections. Therefore, if the patient has a high blood eosinophil count (>500–1000 per μl of blood), it is usually an indicator of a parasitic infection
Depending on the results and the phase of infection the patient is experiencing, your healthcare provider might order further diagnostic tests to confirm the disease, including an ultrasound or CT scan.
Management and treatment for fascioliasis
The treatment of choice for fascioliasis is a drug called triclabendazole. It is the only available drug effective against both immature and adult parasites and can, therefore, be administered in both acute and chronic phases.
The recommended dose for triclabendazole is 10 mg per Kg body weight, which is administered orally (by mouth), usually in a single dose. Most people respond well to this dose. However, in severe cases, the dose may be increased to 20 mg per Kg body weight and administered in two 10 mg per Kg doses, 12-24 hours apart.
According to research studies, the following groups are the most at risk of contracting and transmitting fascioliasis:1
- People who consume a lot of raw freshwater plants, especially watercress
- People living in endemic areas, including Europe and Asia, but also South America, North Africa, and the Middle East
- People living in rural areas that contain a lot of cattle and sheep
- Travellers and immigrants in the United States
Although fascioliasis affects all age groups, school-age children (5-14 year-olds) are believed to have the highest risk when it becomes highly endemic.
Interestingly, contracting fascioliasis by eating (undercooked or raw) sheep or goat liver contaminated with immature parasitic larvae is very rare and has only been reported “under unusual circumstances’’.
Chronic infections caused by F. hepatica lead to several complications including:1
- Ascending cholangitis: This refers to acute inflammation of the bile duct. It usually requires intravenous (IV) antibiotics delivered into a vein, surgery and emergency endoscopic retrograde cholangiopancreatography (ERCP) to directly remove the adult worms from the bile duct, if possible
- Biliary cirrhosis: This refers to a type of chronic liver disease, which, if left untreated, may lead to liver failure
- Sclerosing cholangitis: This refers to scarring and inflammation of the bile ducts, causing liver damage
- Cholangiocarcinoma: This refers to bile duct cancer
How can I prevent fascioliasis?
Although there is no vaccine currently available to prevent fascioliasis, people can protect themselves from the parasitic infection by adhering to the two main tips:
- Avoiding raw watercress consumption, especially in grazing areas prominent with livestock
- Avoiding food and drink consumption if travelling to areas with poor sanitation
How common is fascioliasis?
Fascioliasis is rare, affecting only about 2.4 to 17 million people worldwide.1 Sadly, because of this, fascioliasis is under-reported and underdiagnosed.
When should I see a doctor?
- You suspect you or a family member have/has fascioliasis
- Your symptoms worsen
Fascioliasis is a parasitic infection that is mainly caused by the consumption of raw freshwater plants, including watercress, that are contaminated with infective f. hepatica larvae (‘’metacercariae’’ or ‘’the common liver fluke’’). It is considered to be a type of zoonosis as it is often transmitted from sheep and cattle to humans. Although fascioliasis is spread across Europe, Asia, Central and South America, North Africa and the Middle East, it is a rare infectious disease. For effective transmission to occur, F. hepatica parasites require a carrier (infected plants), an intermediate host (freshwater snail) and a final host (livestock and humans).
The symptoms you might experience vary depending on the phase of infection. There are 3 phases: the incubation phase, the acute phase, and the chronic phase. Please visit your healthcare provider immediately if you suspect you or your loved ones are experiencing any symptoms of fasciolitis. Your healthcare provider will order a few tests to confirm your diagnosis of fascioliasis. After confirming your diagnosis, your healthcare provider will prescribe triclabendazole, the only available drug effective against both immature and adult parasites.
- Good R, Scherbak D. Fascioliasis. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 [cited 2024 Jan 15]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK537032/