Parasitic Flukes: Distribution and Hosts

• Heterophyes heterophyes is a parasitic fluke.
• Metagonimus yokogawi is another parasitic fluke
• Fasciolopsis buski is a giant intestinal fluke.

Distribution

• H. heterophyes is found in Egypt (Nile Delta), the Middle East, and the Far East.
• M. yokogawi is found in the Far East, Russia, and Spain.
• F. buski is found in the Far East.

Habitat

• All three flukes (H. heterophyes, M. yokogawi, and F. buski) reside in the small intestine.
• H. heterophyes and M. yokogawi embed between villi.
• F. buski attaches to the intestinal mucosa.

Definitive Hosts (DH)

• The definitive hosts for H. heterophyes and M. yokogawi are humans and fish-eating animals like dogs and cats. M. yokogawi can also infect pigs.
• The definitive host for F. buski is humans.

Intermediate Hosts (IH)

• Both H. heterophyes and M. yokogawi require two intermediate hosts.
• The first intermediate host for H. heterophyes is the brackish water snail Pirenella conica (amplifier host).
• The second intermediate host for H. heterophyes is Tilapia (Bolty) and Mugil (Boury) fish (transport hosts).
• The first intermediate host for M. yokogawi is the fresh water snail Semisulcospira libertine.
• The second intermediate host for M. yokogawi is Cyprinoid and Salmon fish.
• F. buski utilizes a fresh water snail (Segmentina) as its intermediate host.

Reservoir Hosts (RH)

• The reservoir hosts for H. heterophyes and M. yokogawi are dogs and cats.
• The reservoir host for F. buski is pigs.

Morphology of H. heterophyes

• The shape of H. heterophyes is pear-shaped and unsegmented.
• It measures 1-1.7 mm and has three suckers: oral, ventral, and genital.
• H. heterophyes has a simple intestinal caeca
• It also has one spherical ovary and two oval tests beside each other in the posterior part
• Vitelline glands are on both sides of the posterior half.

Morphology of M. yokogawi

• The shape of M. yokogawi is pear-shaped and unsegmented and measures 1-1.2 mm
• It has two suckers: oral and ventral, with the latter displaced to one side.
• M. yokogawi has simple intestinal caeca
• It also has one sperical ovary and two oval testes obliquely situated in the posterior part
• M. yokogawi has no genital sucker.

Morphology of F. buski

• F. buski is the largest intestinal trematode, measuring 4-7 cm by 1.5 cm.
• It contains an ovale body
• The ventral sucker is larger than the oral sucker.
• F. buski has simple, wavy intestinal caeca, one branched ovary in the middle of the body, and two branched testes in the posterior half with a long cirrus sac

Mode of Infection

• H. heterophyes infection occurs by ingesting encysted metacercaria in insufficiently cooked or inadequately salted fish (Feseekh).
• F. buski infection occurs by ingesting the encysted metacercaria on raw or undercooked water plants.
• M. yokogawi life cycle, infective stage, diagnostic stage, clinical manifestations, diagnosis and treatment are similar to H. heterophyes.

Infective Stage

• The infective stage for both H. heterophyes and F. buski is the encysted metacercaria.

Diagnostic Stage

• For both H. heterophyes and F. buski, diagnosis is determined from eggs in the stool.
• H. heterophyes eggs are oval-shaped, thick-shelled, yellow, mature, and operculated, measuring 30 x 15 μm.

Pathogenesis and Clinical Manifestations of Heterophyiasis

• Light infection: asymptomatic.
• Heavy infection: inflammation of the intestinal mucosa, resulting in chronic intermittent mucous diarrhea and abdominal pain.
• Occasionally, egg emboli may pass through the mesenteric lymphatics and blood vessels to the heart and brain, causing serious complications due to the presence of the genital sucker and the small size of the eggs.

Pathogenesis and Clinical Manifestations of Fasciolopsiasis

• Light infection: asymptomatic or mild abdominal pain and diarrhea due to inflammation and ulceration of the intestinal mucosa.
• Heavy infection: severe inflammation and ulceration of the mucosa with toxic metabolites absorption leading to diarrhea, nausea, vomiting, and protein-losing enteropathy.
• Complications may including hypoalbuminemia, fascial and generalized edema, ascites, vitamin B12 deficiency, anemia, malnutrition, and allergic manifestations, as well as intestinal obstruction.

Diagnosis of Heterophyiasis

• Clinical: abdominal pain and diarrhea with a history of eating insufficiently cooked or salted fish, particularly after Eastern holidays, in a patient from an endemic area.
• Laboratory: finding the characteristic egg in repeated stool examination by direct smear or after stool concentration.

Diagnosis of Fasciolopsiasis

• Clinical: abdominal pain and diarrhea with a history of eating raw aquatic plants in a patient coming from an endemic area.
• Parasitological: finding the characteristic egg in repeated stool examination by direct smear or after stool concentration.
• Complete blood count: eosinophilia and megaloblastic anemia.

Treatment

• Treatment for H. heterophyes: Praziquantel.
• Treatment for F. buski: Praziquantel + treatment of hypoalbuminemia and anemia.

Prevention and Control

• Proper diagnosis and treatment of patients
• Avoid eating insufficiently cooked fish or aquatic plants
• Avoid feeding raw fish to dogs and cats, especially in endemic areas
• Snail control by molluscicides
• For Fasciolopsiasis, avoid using human and pig feces for fertilization of water plants.

Case Study

• A 33-year-old fisherman from the Borolls area presented to the hospital complaining of abdominal pain and diarrhea of 2 weeks' duration.
• The patient reported eating semi-grilled fish during fishing trips.
• Stool examination revealed small operculated 30 x 15 μm eggs.