FASCIOLA

Fascioliasis is a parasitic infection typically caused by Fasciola hepatica, which is also known as "the common liver fluke" or "the sheep liver fluke." A related parasite, Fasciola gigantica, also can infect people. Fascioliasis is found in all 5 continents, in over 50 countries, especially where sheep or cattle are reared. People usually become infected by eating raw watercress or other water plants contaminated with immature parasite larvae. The immature larval flukes migrate through the intestinal wall, the abdominal cavity, and the liver tissue, into the bile ducts, where they develop into mature adult flukes, which produce eggs. The pathology typically is most pronounced in the bile ducts and liver. Fasciola infection is both treatable and preventable.

FAQS

What is fascioliasis?

Fascioliasis is an infectious  disease caused by Fasciola parasites,  which are flat worms referred to as liver flukes. The adult (mature) flukes are  found in the bile ducts and liver of infected people and animals, such as sheep  and cattle. In general, fascioliasis is more common in livestock and other  animals than in people.

Two Fasciola species (types) infect people. The main species is Fasciola hepatica, which is also known  as "the common liver fluke" and "the sheep liver fluke." A related species, Fasciola gigantica, also can infect people.

In what parts of the world is fascioliasis found?

Fascioliasis is found in more  than 50 countries, especially where sheep or cattle are reared. Fasciola hepatica is found in all continents  except Antarctica. Fasciola gigantica has been found in some tropical areas. Except for parts of Western Europe,  human fascioliasis has mainly been documented in developing countries.

How do people get infected with Fasciola?

People get infected by accidentally  ingesting (swallowing) the parasite. The main way this happens is by eating raw  watercress or other contaminated freshwater plants. People also can get  infected by ingesting contaminated water, such as by drinking it or by eating  vegetables that were washed or irrigated with contaminated water.

Can Fasciola be spread directly from one person (or animal) to another?

No. Fasciola cannot be passed directly from one person to another. The eggs passed in the  stool of infected people (and animals) need to develop (mature) in certain types  of freshwater snails, under favorable environmental conditions, to be able to  infect someone else.

Under unusual circumstances, people have gotten infected by eating undercooked sheep or goat liver that contained immature forms of the  parasite.

Can people get infected with Fasciola in the United States?

Yes. It is possible, but few  cases have been reported in published articles.

Approximately 20 cases in Hawaii  over a several-decade period were described in articles in the 1950s. One case  in Florida and at least one case in California linked to watercress have been reported.

However, most reported cases  in the United States have been in people, such as immigrants, who were infected  in countries where fascioliasis is well known to occur.

What are the signs and symptoms of Fasciola infection, and when do they begin?

Some infected people don't  ever feel sick.

Some people feel sick early  on in the infection, while immature flukes are passing (migrating) from the  intestine through the abdominal cavity and liver. Symptoms from the acute  (migratory) phase can start 4 to 7 days after the exposure and can last several  weeks or months.

Some people feel sick during  the chronic phase of the infection, when adult flukes are in the bile ducts (the  duct system of the liver). The symptoms, if any, associated with this phase can  start months to years after the exposure. For example, symptoms can result from  inflammation and blockage of bile ducts.

During  both phases of infection, clinical features can include fever, malaise, abdominal  pain, eosinophilia, hepatomegaly (an enlarged liver), and abnormal liver tests.

What should people do if they think they might be infected with Fasciola?

See their health care provider.

How is Fasciola infection diagnosed?

The infection typically is diagnosed by examining stool  (fecal) specimens under a microscope. The diagnosis is confirmed if Fasciola eggs are seen. More than one  specimen may need to be examined to find the parasite. Certain types of blood  tests also may be helpful for diagnosing Fasciola infection.

Can fascioliasis be treated?

Yes.  Fascioliasis is a treatable disease. Triclabendazole is the drug of choice. It is  given by mouth, usually in one or two doses. Most people respond well to the  treatment.

How can Fasciola infection be prevented?

People can protect  themselves by not eating raw watercress and other water plants, especially from  endemic grazing areas. As always, travelers to areas with poor sanitation  should avoid food and water that might be contaminated. No vaccine is  available to protect people against Fasciola.

EPIDEMIOLOGY & RISK FACTORS

Fascioliasis occurs in many areas of the world and usually  is caused by F. hepatica, which is a  common liver fluke of sheep and cattle. In general, animal fascioliasis is more  common and widespread than human fascioliasis. Even so, the estimated number of  infected people is at least 2.4 million and might be as high as 17 million.

Fasciola  hepatica is  found in more than 50 countries, in all continents except Antarctica. It is  found in parts of Latin America, the Caribbean, Europe, the Middle East,  Africa, Asia, and Oceania. Fasciola  gigantica is less widespread. Human cases have been reported in the  tropics, in parts of Africa and Asia and also in Hawaii.

In some areas where fascioliasis is found, human cases are  uncommon (sporadic). In other areas, human fascioliasis is very common (hyperendemic).  For example, the areas with the highest known rates of human infection are in  the Andean highlands of Bolivia and Peru.

Special conditions are needed for fascioliasis to be present  in an area, and its geographic distribution is very patchy (focal). The  eggs passed in the stool of infected mammals have to develop (mature) in a suitable  aquatic snail host to be able to infect another mammalian host. Requirements  include sufficient moisture and favorable temperatures (above 50°F) that allow  the development of miracidia, reproduction of snails, and larval development  within the snails. These factors also contribute to both the prevalence and level (intensity) of infection.  Prevalence is highest in areas where climatic conditions promote development of  cercariae.

Infective Fasciola larvae (metacercariae) are  found in contaminated water, either stuck to (encysted on) water plants or  floating in the water, often in marshy areas, ponds, or flooded pastures. People  (and animals) typically become infected by eating raw watercress or other  contaminated water plants. The plants may be eaten as a snack or in salads or  sandwiches. People also can get infected by ingesting contaminated water, such  as by drinking it or by eating vegetables that were washed or irrigated with contaminated water. Infection also can result from eating undercooked sheep or goat livers  that contain immature forms of the parasite.

The possibility of becoming  infected in the United States should be considered, despite the fact that few  locally acquired cases have been documented. The prerequisites for the Fasciola life cycle exist in some parts  of the United States. In addition, transmission because of imported  contaminated produce could occur, as has been documented in Europe.

BIOLOGY

Casual Agent:

Fascioliasis is caused by Fasciola hepatica and less often by F. gigantica, which are flat worms classified  as liver flukes (trematodes). Some human cases have been caused by hybrid  species. Additional Fasciola species  have been found in animals.

Life Cycle:

As shown below, Fasciola parasites develop into adult  flukes in the bile ducts of infected mammals, which pass immature Fasciola eggs in their feces. The next  part of the life cycle occurs in freshwater. After several weeks, the eggs  hatch, producing a parasite form known as the miracidium, which then infects a snail  host. Under optimal conditions, the development process in the snail may be  completed in 5 to 7 weeks; cercariae are then shed in the water around the  snail. The cercariae lose their tails when they encyst as metacercariae  (infective larvae) on water plants. In contrast to cercariae, metacercariae have  a hard outer cyst wall and can survive for prolonged periods in wet environments.

Immature Fasciola eggs are discharged in the biliary ducts and in the stool. Eggs become embryonated in water, eggs release miracidiawhich invade a suitable snail intermediate host, including the genera Galba, Fossaria and Pseudosuccinea. In the snail the parasites undergo several developmental stages (sporocysts). The cercariae are released from the snail and encyst as metacercariae on aquatic vegetation or other surfaces. Mammals acquire the infection by eating vegetation containing metacercariae. Humans can become infected by ingesting metacercariae-containing freshwater plants, especially watercress. After ingestion, the metacercariae excyst in the duodenum and migrate through the intestinal wall, the peritoneal cavity, and the liver parenchyma into the biliary ducts, where they develop into adult flukes.

In humans, maturation from metacercariae into adult flukes takes approximately 3 to 4 months. The adult flukes (Fasciola hepatica: up to 30 mm by 13 mm; F. gigantica: up to 75 mm) reside in the large biliary ducts of the mammalian host. Fasciola hepatica infect various animal species, mostly herbivores (plant-eating animals).

Life cycle image and information courtesy of DPDx.

DISEASE

Human fascioliasis is usually recognized as an infection of  the bile ducts and liver, but infection in other parts of the body can occur.

In the early (acute) phase, symptoms can occur as a result  of the parasite's migration from the intestine to and through the liver.  Symptoms can include gastrointestinal problems such as nausea, vomiting, and  abdominal pain/tenderness. Fever, rash, and difficulty breathing may occur.

During the chronic phase (after the parasite settles in the  bile ducts), the clinical manifestations may be similar or more discrete, reflecting inflammation and blockage of bile  ducts, which can be intermittent. Inflammation of the liver, gallbladder, and  pancreas also can occur.

DIAGNOSIS

The standard  way to be sure a person is infected with Fasciola is by seeing the parasite. This is usually done by finding Fasciola eggs in stool (fecal) specimens  examined under a microscope. More than one specimen may need to be examined to  find the parasite. Sometimes eggs are found by examining duodenal contents or  bile.

Infected people don't start  passing eggs until they have been infected for several months; people don't pass  eggs during the acute phase of the infection. Therefore, early on, the  infection has to be diagnosed in other ways than by examining stool. Even  during the chronic phase of infection, it can be difficult to find eggs in  stool specimens from people who have light infections.

Certain types of blood tests can  be helpful for diagnosing Fasciola infection,  including routine blood work and tests that detect antibodies (an immune  response) to the parasite.

PREVENTION AND CONTROL

No vaccine is available to protect people against Fasciola infection.

In some areas of the world where  fascioliasis is found (endemic), special control programs are in place or are planned.  The types of control measures depend on the setting (such as epidemiologic,  ecologic, and cultural factors). Strict control of the growth and sale of  watercress and other edible water plants is important.

Individual people can protect  themselves by not eating raw watercress and other water plants, especially from  endemic grazing areas. As always, travelers to areas with poor sanitation  should avoid food and water that might be contaminated (tainted). Vegetables  grown in fields that might have been irrigated with polluted water should be  thoroughly cooked, as should viscera from potentially infected animals.

For more information view the source:Center for Disease Control

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