What is fascioliasis?
Fascioliasis is a kind of parasitic infection of the liver. Humans are hosts to many different kinds of parasites (called worms in common parlance). Human parasites can infest and live in different cavities and tissues of the body. Most of us are aware of parasites living in the human gut, where they feed on the food we consume. However, some kinds of worms or parasites may also live within the bloodstream or different organs of the body.
One such group of parasitic worms is referred to as trematodes (commonly known as flatworms or flukes). There are many different types of flatworms (or flukes) that can infest and live in different parts of the body. One type of parasitic worm (technically referred to as helminth) prefers to live in the liver. These parasitic worms are known as liver flukes. There are many different types of liver flukes.
Types of Liver Worm
Humans are most commonly infected with a species of liver fluke known as Fasciola hepatica. This species of liver fluke can also infect cattle. Therefore, it is also sometimes referred to as sheep liver fluke. Fasciola gigantica is another species of liver fluke that infects humans. Infection with liver flukes is technically referred to as fascioliasis.
Fasciola hepatica can grow to a length of about one inch (or 30mm). It is one of the largest species of flatworms.
Infection with Fasciola hepatica can occur in both meat eaters and vegetarians. Infections in vegetarians may occur due to consumption of herbs and freshwater vegetables that harbor the larvae of Fasciola hepatica. This is especially the case when these vegetables are consumed in their raw form. Infection with Fasciola hepatica occurs only through diet. This infection cannot spread through personal contact.
In most cases, infection with Fasciola hepatica causes nonspecific and mild symptoms. In some people, infection with Fasciola hepatica may produce a serious disease. This is more likely to be the case when Fasciola hepatica migrates from the liver to other tissues and organs such as the gallbladder, lungs, heart, brain, and skin. However, extrahepatic infection with Fasciola hepatica is not a common occurrence.
Read more on human intestinal worms.
How common is fascioliasis?
The two species of liver flukes responsible for human fascioliasis have different geographic distributions. Fasciola hepatica exists throughout the world (except in Antarctica). However, Fasciola gigantica has a more limited geographic distribution, and is found only in some tropical regions. The majority of cases of fascioliasis are seen in developing nations and in some regions of Western Europe.
In developed countries like the United States, the incidence of liver fluke infection is comparatively less. Most of the cases of fascioliasis in the United States occur in people who have migrated from other endemic regions of the world. Fascioliasis can occur in people of all ages and races. However, adults are most commonly affected. Also, there is a slightly higher risk of infection in males compared to females.
Signs and Symptoms of Fascioliasis
Chronic fascioliasis does not produce any symptoms. The symptoms that may occur in some cases are mild and non-specific. The following are some of the signs and symptoms that may occur in fascioliasis:
- Pain in the upper right abdominal region
- Hepatomegaly (enlargement of the liver)
- Intermittent fever
- Pale skin
- Weight loss
- A general feeling of being unwell (technically referred to as malaise)
The non-specific signs and symptoms mentioned above are not diagnostic of fascioliasis. Blood tests are also not very helpful in diagnosing the presence of liver fluke. A diagnosis of fascioliasis is reached when eggs of the liver fluke are found in the stool of the patient. Imaging studies such as CT scan and abdominal ultrasound may also show the presence of burrowing tracks made by liver flukes in the liver.
In approximately 20% of the cases of fascioliasis, patients may also have urticaria or hives. Children with fascioliasis may exhibit sweating and dizziness. When the liver fluke colonizes organs other than the liver, wheezing and subcutaneous nodules may also occur.
In rare cases, the following severe symptoms may occur due to infection of organs other than the liver:
- Consumption of raw liver of infected animals may lead to a swollen larynx and severe sore throat.
- Infection of the bile ducts (technically referred to as cholangitis) due to liver fluke may lead to jaundice, persistent fever, and severe abdominal pain.
- Infection of the pancreas (especially in children) may lead to nausea, vomiting, fever, and severe abdominal pain.
Spread of Liver Fluke
Both cattle and sheep can carry infections due to Fasciola hepatica and Fasciola gigantica. Consumption of raw livers of cattle, sheep and goat can lead to fascioliasis. Since consumption of raw livers of these animals is not a widespread practice, most human infections are not caused through these animals. Instead, consumption of raw freshwater plants (such as water lettuce, parsley, mint, and watercress) causes most fascioliasis infections in humans.
Adult fluke worms can exist in human liver and bile ducts for many years. During this time, they survive on a diet of human hepatocytes and epithelial cells of the bile ducts. They also produce thousands of eggs, which exit the body through the stool.
Hatching of fluke worm larvae occurs when the eggs of the fluke worm in animal and human stool come in contact with warm water. These larvae (known as miracidia) enter freshwater snails, and mature into another type of free-swimming larvae known as cercaria. The cercaria then attach to the freshwater plants that might be growing in the vicinity, and form cysts.
When humans consume these freshwater plants, the larvae emerge from the cysts and penetrate the walls of the intestine. The larvae eventually reach the liver and mature there, thus establishing infection within the liver and the bile ducts. The mature fluke worm adults then produce more eggs, which again pass out through the intestine.
Prevention of Fascioliasis
The following steps can help in preventing the spread of fascioliasis:
- Avoiding consumption of raw animal livers.
- Using clean water for drinking and cooking food.
- Avoiding consumption of raw vegetables and fruits that grow near pastures where cattle graze.
- Cooking freshwater plants before consumption.
- Soaking raw freshwater plants in 6% vinegar for 5 to 10 minutes before consumption.
Treatment of Fascioliasis
Liver flukes can be effectively eradicated through medications. The drug of choice for the treatment of fascioliasis is triclabendazole. In case of severe symptoms, a short course of corticosteroids may be prescribed by the doctor. Surgical treatment is an option in case of complications such as cholangitis.