Intestinal Flukes Causal Agent: The trematode Heterophyes heterophyes, a minute intestinal fluke . Adults (measuring 1.0 to 1.7 mm by 0.3 to 0.4 mm) .   In addition to humans, various fish-eating mammals (e.g., cats and dogs) and birds can be infected by Heterophyes heterophyes .

Adult of Heterophyes heterophyes Metacercaria

Life Cycle

Geographic Distribution: Egypt, the Middle East, and Far East. Clinical Features: The main symptoms are diarrhea and colicky abdominal pain. colicky pain – which comes and goes   Migration of the eggs to the heart, resulting in potentially fatal myocardial and valvular damage, has been reported from the Philippines.  Migration to other organs (e.g., brain) has also been reported.

Laboratory Diagnosis The diagnosis is based on the microscopic identification of eggs in the stool.  However, the eggs are indistinguishable from those of Metagonimus yokogawai and resemble those of Clonorchis and Opisthorchis. Treatment: Praziquantel* is the drug of choice. 

Metagonimus yokogawai Causal Agent: a minute intestinal fluke (and the smallest human fluke). Adults (measuring 1.0 mm to 2.5 mm by 0.4 mm to 0.75 mm) . Snails of the genus Semisulcospira are the most frequent intermediate host for Metagonimus yokogawai.   In addition to humans, fish-eating mammals (e.g., cats and dogs) and birds can also be infected by M. yokogawai .

Metagonimus yokogawai Adult Egg

Life Cycle

Geographic Distribution: Mostly the Far East, as well as Siberia, Manchuria, the Balkan states, Israel, and Spain. Clinical Features: The main symptoms are diarrhea and colicky abdominal pain.  Migration of the eggs to extra intestinal sites (heart, brain) can occur, with resulting symptoms.

Laboratory Diagnosis The diagnosis is based on the microscopic identification of eggs in the stool.  However, the eggs are indistinguishable from those of Heterophyes heterophyes and resemble those of Clonorchis and Opisthorchis.  Specific diagnosis is based on identification of the adult fluke evacuated after antihelminthic therapy, or found at autopsy.

Laboratory Diagnosis Metagonimus yokogawai, adult fluke resemble Heterophyes heterophyes.  An important distinctive feature is the position of the ventral sucker, which is to the side of the midline with its axis in a diagonal line Treatment: Praziquantel* is the drug of choice

Fasciolopsis buski Causal Agent: The trematode Fasciolopsis buski, the largest intestinal fluke of humans. Adult flukes (20 to 75 mm by 8 to 20 mm) in approximately 3 months, attached to the intestinal wall of the mammalian hosts (humans and pigs) .  The  adults have a life span of about one year.

Adult worm Egg

Life Cycle

Geographic Distribution Asia and the Indian subcontinent, especially in areas where humans raise pigs and consume freshwater plants. Clinical Features Most infections are light and asymptomatic.   In heavier infections, symptoms include diarrhea, abdominal pain, fever, ascites, edema and intestinal obstruction.

Laboratory Diagnosis Microscopic identification of eggs, or more rarely of the adult flukes, in the stool or vomitus is the basis of specific diagnosis. The eggs are indistinguishable from those of Fasciola hepatica

Paragonimus westermani Causal Agent: More than 30 species of trematodes (flukes) of the genus Paragonimus have been reported which infect animals and humans.  Among the more than 10 species reported to infect humans, the most common is P. westermani, the oriental lung fluke Adults (7.5 to 12 mm by 4 to 6 mm).  The worms can also reach other organs and tissues, such as the brain and striated muscles, respectively.

Adult worm

Intermediate host & Metacercaria

Geographic Distribution While P. westermani occurs in the Far East, other species of Paragonimus are encountered in Asia, the Americas, and Africa.

Life Cycle: Life Cycle:                                                                              

Clinical Features The acute phase (invasion and migration) may be marked by diarrhea, abdominal pain, fever, cough, urticaria, hepatosplenomegaly, pulmonary abnormalities, and eosinophilia. During the chronic phase, pulmonary manifestations include cough, expectoration of discolored sputum, hemoptysis, and chest radiographic abnormalities.   Extrapulmonary locations of the adult worms result in more severe manifestations, especially when the brain is involved.

Laboratory Diagnosis Diagnosis is based on microscopic demonstration of eggs in stool or sputum, but these are not present until 2 to 3 months after infection.   (Eggs are also occasionally encountered in effusion fluid or biopsy material.)   Concentration techniques may be necessary in patients with light infections. Biopsy may allow diagnostic confirmation and species identification when an adult or developing fluke is recovered.

Microscopy A Egg of Paragonimus westermani. They are yellow-brown, ovoidal or elongate, with a thick shell, and often asymmetrical with one end slightly flattened.  At the large end, the operculum is clearly visible.  The opposite (abopercular) end is thickened.  The eggs of P. westermani are excreted unembryonated. A                                                          A Treatment: Praziquantel* is the drug of choice to treat paragonimiasis