Fluke infections

Fluke infections are diseases of the digestive tract and other organ systemscaused by parasitic flatworms (Trematodes) that involve hosts other than human beings. Trematode comes from a Greek word that means having holes and refers to the external suckers that adult flukes use to draw nourishment from their hosts. Fluke infections are contracted by eating uncooked fish, plants, oranimals from fluke-infected waters. In humans, there are liver and lung flukes. Diseases caused by liver flukes include fascioliasis, opisthorchiasis, andclonorchiasis. Cases of liver fluke infection have been reported in Europe,the United States, the Middle East, China, Japan, and Africa. Diseases causedby lung flukes include paragonimiasis, a common infection in the Far East, Southeast Asia, Africa, Central and South America, Indonesia, and the PacificIslands. It is estimated that between 40 million and 100 million people worldwide suffer from either liver or lung fluke infections. Liver and lung flukesenter through the mouth and can infect anyone. The symptoms differ accordingto the type of fluke involved but always include: Most people don't developsymptoms; the early symptoms are not unique to these diseases alone; infection does not confer immunity against re-infection by the same or other speciesof flukes; and infection is usually associated with eating uncooked fish, plants, or animals that live in fresh water.

Fascioliasis is caused by Fasciola hepatica, the sheep liver fluke. Humans become infected when they eat watercress, water chestnuts, or other plants covered with the encysted metacercariae. The metacercariae enter the liver, where they inflame and destroy tissue. After 10-15 weeks in the liver, theadult flukes move to the bile ducts and produce eggs. Acute fascioliasis is marked by abdominal pain with headache, loss of appetite, anemia, and vomiting. Some patients develop hives, muscle pains, or a yellow color to theskin and whites of the eyes (jaundice). Chronic disease may produce complications, including blockage of the bile ducts or the migration of adult flukes to other body parts.

Opisthorchiasis and clonorchiasis are caused by Clonorchis sinensis, the Chinese liver fluke, Opisthorchis viverrini or O. felineus and affect more than 20 million people in Japan, China, Southeast Asia, and India. The symptoms of opisthorchiasis and clonorchiasis are similar to those of fascioliasis and include acute and chronic forms. In acute infection, the patient may be tired, have a low-grade fever, pains in the joints, a swollen liver, abdominal pain, and a skin rash. The acute syndrome may be difficult todiagnose because the fluke eggs don't appear in the patient's stool for three to four weeks. Patients with chronic disease experience a loss of appetite,fatigue, low-grade fever, diarrhea, and an enlarged liver that feels sore when the abdomen is pressed.

Paragonimiasis is caused by a lung fluke, either Paragonimus westermani or P. skrjabini. These flukes are larger than liver flukes and alsoinfect meat- or fish-eating animals. In humans, the metacercariae migrate tothe lungs or the brain in 1% of cases. In the lungs, the flukes lay their eggs and form areas of inflammation covered with a thin layer of fibrous tissue.These areas may eventually rupture, causing the patient to cough up fluke eggs, blood, and inflamed tissue. It takes about six weeks for the eggs to appear. Patients with lung infections may have chest pain, fever, and rust-colored or bloody sputum. Lung infections can lead to lung abscess, pneumonia, or bronchitis. Patients with fluke infections of the brain may experienceseizures or a fatal inflammation of brain tissue called encephalitis.Some patients also develop diarrhea and abdominal pain or lumps under the skin.

Diagnosis of fluke infections is based on the patient's history and identification of the fluke's eggs or adult forms. In the United States, stool specimens or body fluid samples may be sent to a laboratory with experts in unusualdiseases to identify the parasite. In some cases, adult flukes are found in the patient's stools, vomit, sputum, or skin lumps (for lung flukes). In lungflukes, it's important to rule out tuberculosis through a tuberculosis skin test and a chest x ray. Blood tests may be somewhat useful in diagnosing flukeinfections. In some cases, computed tomography scans (CT scans) or ultrasound scans of the patient's chest or brain (for lung flukes) or abdomen (for liver flukes), are useful. Fluke infections are treated with medicationssuch as triclabendazole, praziquantel, bithionol, albendazole, and mebendazole. Treatment varies from several days to several weeks. Cure rates range from50-95%. Most patients experience mild side effects from these drugs. The prognosis for recovery from liver fluke infections is good, although patients with serious infections may be more vulnerable to other diseases. Most patientswith lung fluke infections also recover, however, severe infections of the brain can cause death. There are no vaccines against fluke infections. Prevention includes: Boiling or purifying drinking water, avoiding raw or undercooked fish or salads made from fresh aquatic plants, thoroughly cooking all foodeaten in areas with fluke infestations, and controlling or killing the snailsthat are the flukes' intermediate hosts.

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