Liver Fluke Life Cycle

What Is A Liver Fluke?

Common liver flukes or Fasciola hepatica are parasites causing the liver fluke disease or Fascioliasis in the liver of human beings. 

Liver fluke: An Overview

The liver fluke parasites belong to the Phylum Platyhelminthes. The main reason behind the liver fluke disease is the entry of the immature liver fluke parasites into the liver and their presence in the bile ducts. All the grazing animals such as sheep, cattle and mammals like human beings are infected by liver flukes. Generally, liver flukes are found near the water bodies such as river banks, slow streaming river, irrigation channels, etc because these areas are favourable for hatching eggs of the liver fluke. 

Various Stages of the life Cycle of Liver Fluke

The life cycle of liver flukes is categorized into four stages namely The Egg (stage 1), The Intermediate Host (stage 2), The Young Fluke (stage 3) and The Adult (stage 4). All the four stages are described vividly in the following:

Life Cycle Chart


1. The Egg (stage 1): 

The immature eggs are laid by the adult female liver fluke after fertilization. The eggs are laid in the bile duct and come out into the environment through the faeces. The eggs become embryonated if and when comes into contact with the water and larvae called miracidia is formed.

2. The Intermediate Host (stage 2)

A snail is infected by a miracidia larvae and it transforms the miracidia larvae into the cercaria larvae. Hence, the snail is the intermediate host in the above-mentioned scenario and cercaria larvae can swim in the water with the help of the long tail. After that, the snail is left behind by the cercaria larvae and it develops itself independently looking for the vegetation. Cercaria larvae form cysts named metacercariae. Metacercariae set the stage for an infection in animals such as sheep and cattle and in human beings. A rigid hard outer layer helps the metacercariae survive for a long period of time. The cysts produce immature eggs into the small intestine of the human host when and if human beings intake the raw freshwater plant or fish contaminated with the cysts. 

3. The Young Fluke (stage 3): 

After stage 2 the small intestine wall is penetrated by the fluke parasite and it enters into the peritoneal cavity. Next, it directly comes in contact with the liver and it begins feeding on liver cells. The above phenomenon happens a few days after the host comes in contact with the parasite. The young flukes enter into the bile duct and transform into adult liver flukes after eating numerous liver cells.

4. The Adult (stage 4): 

It takes approximately three months for the transformation of the metacercariae into the adult liver fluke. The approximate length of an adult liver fluke is around 3 cm. An adult female liver fluke can lay 20,000 to 25,000 eggs per day in her last stage of pregnancy. 


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What Are The Symptoms of Liver Fluke Infection?

There are various symptoms of liver fluke disease which are:

  • Acute abdominal pain

  • Fever

  • Vomiting

  • Nausea

  • Diarrhoea

  • Hives

  • Malaise


Apart from the above-mentioned symptoms, there may be some other rare complications associated with heavy liver fluke infections which include the formation of stone, recurrent infections of the biliary system and cholangiocarcinoma (bile duct cancer).


What are The Treatment Options for Liver Fluke Infection?

Medication or Surgery:

Liver flukes can be cured completely with the help of the medication. The most common medication to treat the liver fluke is triclabendazole. Generally, the drug is given in one or two doses orally and most people soundly respond to this treatment. 

Sometimes doctors prescribe a short course of corticosteroids for severe phases with acute symptoms. 

In very rare cases surgery is required for related long term complications such as cholangitis (infection of the bile duct).


Alternative Treatments:

There are some alternative and unusual therapies for parasite infection. It is recommended to take goldenseal for parasitic infections, parasite cleanses and colonic irrigation. 

How to Get Relief From Liver Fluke Symptoms?

Acetaminophen (Tylenol) can be taken to get relief from the abdominal pain and to reduce fever. Nausea and vomiting can be reduced by anti-nausea medications. But the root of disease cannot be treated by these medications. Hence, diagnosing the liver fluke infection and commencing the treatment as early as possible is always suggested.

What Are The Risk Factors of Liver Fluke Infection?

Liver fluke infection is a very common disease in some particular parts of the world. People from these parts of the world are obviously at a higher risk of infection. The risk factor is also greater for those people who travel to those particular parts of the world. If someone has a recent history of taking raw or undercooked fish or watercress especially while in these areas should undergo routine testing. Liver fluke infection is not contagious. But still, the family members of the affected persons may be at risk of infection simply because of eating the same food. 

How To Diagnose Liver Fluke Infection?

The diagnosis of liver fluke infection may be done by finding yellow-brown eggs in the stool. The eggs cannot be differentiated from the eggs of Fascioloides magna. But these eggs are rarely passed to sheep, goats or cattle. A false positive-result to the test can occur if a patient has taken infected liver and the eggs pass through the body and out via the faeces. The accurate test to detect liver fluke infection is the enzyme-linked immunosorbent assay (ELISA) test. 

Prevention:

For every disease, it is universally true that ‘prevention is better than cure’. Everyone must be aware of the fact that liver fluke infection can easily be cured. The most effective and proper way to prevent a liver fluke infection is to ensure that freshwater fish and watercress are properly cooked before consuming them. People must avoid food and water that could potentially be contaminated with the parasites while travelling to areas with least sanitation. Presently there is no vaccine available to prevent liver fluke infections. 

Liver flukes are initially big, flat parasitic worms that are found in the liver, resulting in a disease known as fascioliasis. The parasites are mostly found in parts of Australia and the regions with several water bodies such as irrigation channels, slow-streaming rivers and so on. It is quite a natural infection and can be cured completely with the help of medications. Generally, complications don’t arise due to liver flukes infection.

FAQ (Frequently Asked Questions)

1. How do snails get infected in summer?

Snail populations multiply in a rapid manner and snails are invaded by hatching miracidia from May to July. The massive numbers of cercariae are shed by the snails onto pasture during July to October if wet weather continues. On the other hand, fewer snails appear and fewer fluke eggs hatch if the climate is dry and cold in May and July. In the autumn, the level of contamination is much lower and at a certain point of time, it may disappear. Clinical fasciolosis caused from summer infection of snails occurs from ingestion of large numbers of metacercariae over a short span of time in July to October.

2. How do snails get infected in winter?

In very rare occasions snails get infected in late summer or early autumn and growth within infected snails become dormant and hibernate. The cercariae will not get infected onto the pasture until the next spring. This can generate a primary and prominent infection in herds or flocks in the spring.

3. What is Fasciolosis?

Liver fluke disease affects the sheep in three different clinical forms – acute, subacute and chronic fasciolosis. The type of clinical forms depends upon the numbers of infective metacercariae ingested and the actual time frame at which they are ingested. According to a recent report, milder winters and wetter summers have experienced changing patterns in parasite epidemiology and reported disease with earlier seasonal reports in severe disease.   

4. What is fluke quarantine?

At the time of buying of sheep, fluke quarantine treatment strategies must be taken into consideration on the basis of risk posed by the sheep and the risk status of the farm. The strategies must be expedited by the consultation with a vet or animal health advisor. The three main reasons behind the fluke quarantine are:


1. There is a possibility of the introduction of sheep onto a farm with no known snail habitat. Hence, there might not be any history of fluke infection. The risk factor behind the introduced fluke on the farm is very minimal and treatment should be done accordingly. 


2. The farm may have regions identified as a favourable habitat for snails but no history of fluke infection. The risk of introduced fluke establishing on the farm is considered to be prominent. Therefore to remove all the treatment is necessary.


3. It is a high possibility that the liver fluke will become endemic. So, introducing small numbers of fluke will not be a serious issue.