Introduction
Fascioliasis is also known as the common liver fluke or the sheep liver fluke. Fasciola hepatica and a related parasite, Fasciola gigantica, are the main causative agent. Fascioliasis is found all around the world in sheep or cattle. Generally, people become infected by consuming raw water plants like watercress infected with immature parasite larvae. The infection mostly affects the liver and bile ducts. Fasciola infection can be prevented by taking proper precautions.
What Is the Causative Agent of Fascioliasis?
Fascioliasis is caused by Fasciola parasites or flatworms referred to as liver flukes. These young worms enter the intestinal wall and the abdominal cavity to reach the liver tissue and the bile ducts. These flukes mature in the bile duct and liver tissues of infected people or animals like sheep and cattle. Fascioliasis occurs more commonly in animals or livestock than in humans.
The infection is caused by two species:
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Fasciola hepatica, measures up to 30 mm by 15 mm (main species).
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Fasciola gigantica, measures up to 75 mm by 15 mm (related species).
These parasites are found in domestic and wild ruminants that act as the main host. In Africa and Asia, both these species are endemic. Usually, they occur in the intermediate morphologic form that shows genetic traits of both species and portrays unusual prodigy levels, and does not produce sperm. Various studies are being conducted on the origin and nature of these forms.
How Is Fascioliasis Transmitted to Humans?
The infection is transmitted to humans by accidental exposure to the parasite. Usually, humans get infected by eating freshwater plants like watercress. This infection can also spread by consuming infected water or by eating vegetables that were washed with contaminated water. The infection by Fasciola is not transmitted directly from one person to another. The eggs of the parasite released in the stool of infected individuals or animals are required to first mature in certain freshwater snails under optimal environmental conditions. After maturation, these parasites can cause infection in humans and animals. Mostly, the infection occurs by consuming undercooked goat liver or sheep contaminated with immature parasites.
What Are the Clinical Manifestations of Fascioliasis?
The main clinical features of fascioliasis include:
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Malaise.
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Nausea and vomiting.
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Eosinophilia (increased white blood cell count).
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Hepatomegaly (an enlarged liver).
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Abnormal liver tests.
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Rash.
Sometimes the infection does not produce any symptoms of illness. Some individuals develop symptoms early when immature flukes migrate from the intestine and reach the abdominal cavity and liver. The symptoms migratory acute phase develop after 4 to 7 days of exposure and can be present for several weeks or months. Sometimes the illness is noticed in patients during the chronic phase of this infection. In this phase, the adult flukes are present in the bile ducts, and the symptoms of this phase may take months to years to develop after the exposure. Chronic infection can lead to inflammation and blockage of bile ducts, along with swelling in the gall bladder and pancreas.
What Is the Epidemiology Of Fascioliasis?
In some regions of the world, human cases of fascioliasis are uncommon. However, in other regions, human fascioliasis is hyperendemic, like the Andean highlands of Bolivia and Peru (the areas with the highest cases of human infections). The infection has affected around two million people around the globe. However, Fascioliasis occurs more commonly in humans than in animals. Fasciola hepatica has been identified in more than 70 countries, except Antarctica. It is present in Latin America, Europe, the Middle East, the Caribbean, Asia, Africa, and Oceania. Fasciola gigantica has a more limited geographic presence. Cases in humans have been documented in tropical regions, Asia, Africa, and also in Hawaii.
How Is Fascioliasis Diagnosed?
The typical method for diagnosis of this infection is by seeing the parasite. This can be achieved by examining Fasciola eggs in stool or fecal samples under a microscope. Usually, more than a single sample is required to be examined to identify the parasite. Eggs may also be found by examining bile or duodenal contents. Eggs cannot be found in the stool of infected patients even after several months of exposure to the parasite. Therefore, the infection cannot be diagnosed through a microscopic examination of the stool initially. Furthermore, sometimes in chronic infections, finding eggs in stool specimens from individuals with light infections can be difficult. In such cases, certain blood tests can be used to detect the Fasciola infection, including routine blood tests that detect antibodies (that show an immune response) to the parasite.
How Is Fascioliasis Treated?
The primary step to ensure the treatment is successful is to make sure the diagnosis is accurate. The drug of choice for the treatment of Fascioliasis is Triclabendazole. The drug is given orally and is usually divided into two doses. The medication is effective in most cases.
How Can Fascioliasis Be Prevented?
Presently, no vaccine is available for protection against Fasciola infection. Special control programs are initiated in certain parts of the world where fascioliasis is endemic. The control measures usually depend on epidemiologic, ecologic, and cultural factors. The sale and growth of watercress and other edible water plants should be under strict control. Individuals can protect themselves by not consuming raw watercress and other water plants, particularly in Fasciola-endemic regions. People traveling to areas with poor sanitation should not consume food and water that might be contaminated to avoid infection. Potentially infected plants and animal parts should be cooked thoroughly before eating.
Conclusion
The Fasciola larvae are usually found in contaminated water like water plants or plants floating in ponds, marshy areas, or flooded pastures. Humans and animals become infected mainly by eating raw watercress or other contaminated water plants. For instance, when these plants are eaten in salads or sandwiches. The chances of being infected in the United States should be evaluated since cases have been recorded in some local areas. The requirements for the survival of this parasite are present in some parts of the United States. In addition, the infection can spread through imported contaminated products, as reported in Europe.
