Fluke Infections

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Sunday, April 07, 2002 8:28 PM

Fluke Infections

 

 

http://www.ahealthyme.com/topic/topic100586836

 

Fluke Infections.

 

Definition

Fluke infections are diseases of the digestive tract and other organ

systems caused by several different species of parasitic flatworms

(Trematodes) that have complex life cycles involving 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, or animals from fluke-infected waters.

Symptoms vary according to the type of fluke infection.

 

Description

In humans, fluke infections can be classified according to those

diseases caused by liver flukes and those caused by lung flukes.

Diseases caused by liver flukes include fascioliasis,

opisthorchiasis, and clonorchiasis. Cases of liver fluke infection

have been reported in Europe and the United States, as well as the

Middle East, China, Japan, and Africa. Diseases caused by lung flukes

include paragonimiasis. Paragonimiasis is a common infection in the

Far East, Southeast Asia, Africa, Central and South America,

Indonesia, and the Pacific Islands. It is estimated that between 40

million and 100 million people worldwide suffer from either liver or

lung fluke infections.

 

In their adult stage, liver and lung flukes are symmetrical in shape,

ranging between 1/4?1 inch in length, and look somewhat like long,

plump leaves or blades of grass. They enter through the mouth and can

infect any person at any age.

 

Causes and symptoms

The symptoms of fluke infection differ somewhat according to the type

of fluke involved. All forms of liver and lung fluke infection,

however, have the following characteristics:

.. Most persons who get infected do not develop symptoms

(asymptomatic).

 

.. The early symptoms of an acute fluke infection are not unique to

these diseases alone (nonspecific symptoms).

 

.. Infection does not confer immunity against re-infection by the

same species or infection by other species of flukes.

 

.. Infection is usually associated with eating uncooked fish, plants,

or animals that live in fresh water.

 

 

Fascioliasis

Fascioliasis is caused by Fasciola hepatica, the sheep liver fluke.

The fluke has a three-part life cycle that begins when eggs from a

host's feces are deposited in water. The eggs release free-swimming

larvae (miracidia) that infect snails. The snails then release free-

swimming larvae with tails (cercariae) that form cysts containing

larvae in the infective stage (metacercariae) on vegetation growing

in fresh water. Humans become infected when they eat watercress,

water chestnuts, or other plants covered with the encysted

metacercariae.

 

When a person eats contaminated plants, the cysts are broken open in

the digestive system, and the metacercariae leave their cysts, pass

through the wall of the intestine, and enter the liver, where they

cause inflammation and destroy tissue. After a period of 10?15 weeks

in the liver, the adult 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 the skin and whites of the eyes

(jaundice ). Chronic forms of the disease may produce complications,

including blockage of the bile ducts or the migration of adult flukes

to other parts of the body.

 

Opisthorchiasis and clonorchiasis

These infections are caused by Clonorchis sinensis, the Chinese liver

fluke, and Opisthorchis viverrini or O. felineus. The diseases are

widespread, affecting more than 20 million people in Japan, China,

Southeast Asia, and India. The life cycle of these liver flukes is

similar to that of F. hepatica except that the etacercariae are

encysted in freshwater fish rather than on plants. Dogs, cats, and

other mammals that eat raw fish can be infected with opisthorchiasis

and clonorchiasis.

 

The symptoms of opisthorchiasis and clonorchiasis are similar to

those of fascioliasis and include both 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 to diagnose because the

fluke eggs do not appear in the patient's stool for three to four

weeks after infection. Patients with the chronic form of the disease

experience a loss of appetite, fatigue, low-grade fever, diarrhea ,

and an enlarged liver that feels sore when the abdomen is pressed.

 

Paragonimiasis

Paragonimiasis is caused by a lung fluke, either Paragonimus

westermani or P. skrjabini. These flukes are larger than liver flukes

and infect meat- or fish-eating animals as well as humans. Their life

cycle is similar to that of liver flukes except that their encysted

larvae infect crabs and crayfish rather than plants or fish. Humans

can ingest the encysted metacercariae from drinking contaminated

water or eating raw or undercooked crabs and crayfish.

 

In humans, the metacercariae are released from their cysts in the

small intestine and migrate to the 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

of infection may eventually rupture, causing the patient to cough up

fluke eggs, blood, and inflamed tissue. The period between the

beginning of the infection and the appearance of the eggs during

coughing is about six weeks. Patients with lung infections may have

chest pain and fever as well as rust-colored or bloody sputum. Lung

infections can lead to lung abscess , pneumonia , or bronchitis .

Patients with fluke infections of the brain may experience seizures

or a fatal inflammation of brain tissue called encephalitis . Some

patients also develop diarrhea and abdominal pain or lumps under the

skin that contain adult flukes.

 

Diagnosis

Diagnosis of fluke infections is based on a combination of the

patient's history, particularly travel or residence in areas known to

have flukes, and identification of the fluke's eggs or adult forms.

In some patients, the eggs are found in fluid from the lungs, bile

duct, or small intestine. Samples of these fluids can be obtained

with a suction instrument (aspirator). Because most types of fluke

infections are rare in the United States, stool specimens or body

fluid samples may need to be sent to a laboratory with experts in

unusual diseases or conditions to identify the specific parasite. In

some cases, adult flukes may be found in the patient's stools, vomit,

sputum, or skin lumps (for lung flukes). In the case of lung flukes,

it is important for the doctor to rule out tuberculosis as a possible

diagnosis. A tuberculosis skin test and chest x ray will usually be

sufficient to do this.

 

Blood tests may be useful in diagnosing fluke infections, but their

usefulness is limited because of cross-reactions. A cross-reaction

occurs in blood testing when a particular disease agent reacts with

antibodies specific to another disease agent. This result means that

the doctor may know that the person is infected by flukes but cannot

tell from the blood test alone which specific type of fluke is

causing the disease. In addition, blood tests for fluke infections

cannot distinguish between past and current infections. In some

cases, sophisticated imaging techniques, such as 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 in

confirming a diagnosis of fluke infection.

 

Treatment

Liver and lung fluke infections are treated with medications. These

include triclabendazole, praziquantel, bithionol, albendazole, and

mebendazole. Praziquantel works by paralyzing the flukes' suckers,

forcing them to drop away from the walls of the host's blood vessels.

In the United States, bithionol is available only from the Centers

for Disease Control (CDC). Depending on the species of fluke and the

severity of infection, the course of treatment can vary from several

days to several weeks. Cure rates vary from 50?95%. Most patients

experience mild temporary side effects from these drugs, including

diarrhea, dizziness , or headache.

 

Prognosis

The prognosis for recovery from liver fluke infections is good,

although patients with serious infections may be more vulnerable to

other diseases, particularly if significant liver damage has

occurred. Most patients with lung fluke infections also recover,

however, severe infections of the brain can cause death from the

destruction of central nervous system or brain tissue.

 

Prevention

No vaccines have been developed that are effective against lung or

liver fluke infections. Prevention of these infections includes the

following measures:

.. Boiling or purifying drinking water.

 

.. Avoiding raw or undercooked fish or salads made from fresh aquatic

plants. All food eaten in areas with fluke infestations should be

cooked thoroughly. Pickling or smoking will not kill fluke cysts in

fish or shellfish.

 

.. Control or eradication of the snails that serve as the flukes'

intermediate hosts.

 

 

Key Terms

 

.. Aspirator

A medical instrument that uses suction to withdraw fluids from the

lungs, digestive tract, or other parts of the body for laboratory

testing.

 

.. Asymptomatic

Persons who carry a disease and are usually capable of transmitting

the disease but, who do not exhibit symptoms of the disease are said

to be asymptomatic.

 

.. Cercaria (plural, cercariae)

An intermediate-stage of the fluke larva, released into water by

infected snails.

 

.. Cross-reaction

A reaction that occurs in blood testing when a disease agent reacts

to the specific antibody for another disease agent. Cross-reactions

are common in blood tests for fluke infections because the different

species are closely related.

 

.. Encysted

Enclosed in a cyst or capsule. Flukes spend part of their life cycle

as encysted larvae.

 

.. Fluke

A parasitic flatworm that has external suckers. Flukes are sometimes

called trematodes.

 

.. Host

The living animal that supplies nutrition to a parasite.

 

.. Jaundice

Yellowing of the skin and the whites of the eyes as a result of

excess bile in the blood due to an improperly functioning liver.

 

.. Metacercaria (plural, metacercariae)

The encysted stage of a fluke larva that produces infection in human

beings.

 

.. Miracidium (plural, miracidia)

The free-swimming larval form in the life cycle of the liver fluke.

 

.. Parasite

An organism that lives on or inside an animal of a different species

and feeds on it or draws nutrients from it.

 

.. Trematode

Parasitic flatworms or another name for fluke, taken from a Greek

word that means having holes.

 

 

Further Reading

 

Books

 

Goldsmith, Robert S. " Infectious Diseases: Protozoal & Helminthic. "

In Current Medical Diagnosis & Treatment 1998, edited by Lawrence M.

Tierney Jr., et al. Stamford, CT: Appleton & Lange, 1998.

Houston, Stan, and Kinga Kowalewska-Grochowska. " Other Trematodes. "

In Current Diagnosis 9, edited by Rex B. Conn, et al. Philadelphia:

W. B. Saunders Company, 1997.

 

Howell, M. J. " Fascioliasis. " In Encyclopedia of Immunology, Vol. II,

edited by Ivan M. Roitt and Peter J. Delves. London: Academic Press,

1992.

 

Phillips, Elizabeth, and Jay S. Keystone. " Intestinal Parasites. " In

Conn's Current Therapy, edited by Robert E. Rakel. Philadelphia: W.

B. Saunders Company, 1997.

 

" Praziquantel. " In Nurses Drug Guide 1995, edited by Billie Ann

Wilson, et al. Norwalk, CT: Appleton & Lange, 1995.

 

Sirisinha, Stitaya. " Opisthorchiasis-Clonorchiasis. " In Encyclopedia

of Immunology, Vol. III, edited by Ivan M. Roitt and Peter J. Delves.

London: Academic Press, 1992.

 

Weinberg, Adriana, and Myron J. Levin. " Infections: Parasitic &

Mycotic. " In Current Pediatric Diagnosis & Treatment, edited by

William W. Hay Jr., et al. Stamford, CT: Appleton & Lange, 1997.

 

Copyright 1999-2001. The Thomson Corporation. All rights reserved.

The PDR® Encyclopedia of Medicine is a trademark of Medical

Economics, Inc.

 

First published July 14, 1999

 

 

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