Intestinal Parasite Infections From Flukes -- Description, Diagnosis, Treatment

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Intestinal Parasite Infections From Flukes -- Description, Diagnosis,

Treatment

 

Trematodes (or flukes) are flat worms that cause significant morbidity

in human hosts. These parasites have complex life cycles involving

multiple generations and hosts. Trematodes causing significant human

disease include Fasciolopsis buski, the heterophyids (Metagonimus

yokogawai and Heterophyes heterophyes) and the amphistomes

(Gastrodiscoides hominis).

 

Many flukes are microscopically small, but some species grow to 2 " -

3 " in length. The following pictures portray a few of the larger

intestinal and liver flukes. The left picture is an intestinal fluke,

the middle and right pictures are liver flukes. The right picture is a

sheep liver fluke encysted in a liver bile duct -- uncoiled it would

be about 1 inch long.

 

 

FASCIOLOPSIS BUSKI

 

F. buski is the largest trematode to infect man and is commonly found

throughout central and southeast Asia.

 

Life cycle. F. buski commonly infects both humans and pigs. Eggs are

passed in the host feces and hatch in freshwater into miracidia. The

miracidia are ingested by snails and develop into cercariae. The

cercariae are passed by the host snail and encyst upon a variety of

water plants including red caltrop, water chestnut, water bamboo, and

water lotus. Humans ingest the shoots of these plants that contain as

many as 200 metacercariae. The metacercariae migrate into the human

duodenum and jejunum and attach to the intestinal mucosa. The adult

worm develops within approximately 3 months.

 

Clinical manifestations. The majority of infections caused by F. buski

are asymptomatic. When present, initial symptoms are usually abdominal

pain and diarrhea. Severe infection, characterized by a heavy worm

load, may be associated with severe non-bloody diarrhea, anemia,

facial edema, peripheral edema, ascites, and intestinal obstruction.

Erosion into the intestinal wall can lead to mucosal ulceration, GI

hemorrhage, and/or abscess formation. Absorption of toxic metabolites

may lead to the development of systemic symptoms.

 

Diagnosis, treatment, and prevention. The diagnosis is made by

identification of typical eggs in the host feces, where occasionally,

adult worms are passed. The treatment of choice is 75 mg/kg of

praziquantel given in three divided doses over a single day. Infection

with F. buski can be prevented with the boiling of freshwater

vegetables and nuts prior to ingestion.

HETEROPHYIDS

 

Humans are infected by the small flukes Metagonimus yokogawai and

Heterophyes heterophyes by eating raw fish.(35) Both M. yokogawai and

H. heterophyes are primarily intestinal flukes of dogs and cats. Human

infection with M. yokogawai occurs in Asia, the Middle East, and

Siberia. H. heterophyes infection occurs in southeast Asia and

northwest Africa.

 

Life cycle. The life cycles of M. yokogawai and H. heterophyes are

identical. Eggs are ingested by snails that are the first intermediate

hosts. The eggs mature into cercariae and are passed by the host

snail. The cercariae penetrate the skin of freshwater fish and migrate

to the muscle where they mature into metacercariae. Infected raw fish

are ingested by humans. The metacercariae mature into adult worms in

the duodenum and jejunum.

 

Clinical manifestations. The majority of M. yokogawai and H.

heterophyes infections are asymptomatic. Abdominal pain and diarrhea

may accompany severe infection. Occasionally, eggs may penetrate the

intestinal mucosa and reach the intestinal lymphatics where migration

into the heart or central nervous system can occur. Granulomatous

reaction may result from this migration; however, symptoms are

distinctly uncommon.

 

Diagnosis, treatment, and prevention. The diagnosis is made through

the identification of typical eggs of M. yokogawai or H. heterophyes

in the host feces. Treatment of these flukes is the same as that for

F. buski. Infection with these worms can be prevented with proper

cooking of fish prior to ingestion.

AMPHISTOMES

 

Gastrodiscoides hominis is a common parasite in humans in India and

the former Soviet Union, where it is prevalent in pigs. Humans become

infected through ingestion of infected plants.

 

Life cycle. The life cycle of G. hominis is not completely known but

is believed to be similar to that of F. buski, with snails and aquatic

plants acting as intermediate hosts.

 

Clinical manifestations. Most infections are asymptomatic. Severe

infection is associated with abdominal pain and diarrhea.

 

Diagnosis, treatment, and prevention. The diagnosis is made through

the identification of typical eggs in the host feces. Treatment is the

same as that for M. yokogawai or H. heterophyes. Soapsuds enemas have

been reported to be as effective as chemotherapy in removing the worms.

 

Source: Dr. David Bernstein, M.D.