Clinical Parasitology: Trematodes (Flukes)

• Lecture is on Clinical Parasitology

Trematodes (Flukes) General Characteristics

• Flat-shaped organisms
• Possess oral and ventral hooks or cup-shaped suckers for attachment
• Hermaphroditic, with the exception of Schistosomes
• Require an intermediate host for development
• The reproductive system is well-developed for efficient propagation
• Mollusks serve as the first intermediate host in the life cycle
• Adult trematodes have an oral sucker and a ventral sucker called an acetabulum
• Some species have a genital sucker or gonotyl
• All trematodes require two intermediate hosts to complete their life cycle
• The infective stage is the encysted larva, called the metacercaria
• All trematodes produce operculated eggs
• Adult flukes are hermaphroditic, except for some species
• The body is covered by an integument that may feature spines, papillae, or tubercles
• They lack a body cavity and circulatory/respiratory organs with an incomplete digestive system
• The excretory system consists of flame cells and collecting tubules, leading to a posterior median bladder opening

Stages of Development

• Egg stage initiates the cycle
• Miracidium is the first larval stage, emerging from the egg in fresh water
• Sporocyst emerges from the miracidium as a sac-like structure containing the larva
• Rediae is a larval stage occurring in the sporocyst
• Cercariae is the final development stage in the snail and are motile using a tail
• Metacercariae is the encysted form found in the second intermediate host
• Adult is the mature stage

Fasciolopsis buski (Giant Intestinal Fluke):

• Causes fasciolopsiasis in central & Southeast Asia
• Endemic to areas including China, Korea, and India
• Transmission occurs through ingesting raw aquatic vegetation such as water chestnuts with encysted eggs
• Diagnosis involves detecting characteristic eggs in feces
• Elongated oval fluke (2 to 7 cm long)
• Lives in the small intestine of man

Hosts

• Humans and pigs are the definitive hosts
• Snails such as Segmentina and Hippeutis serve as the first intermediate hosts
• Aquatic vegetation like Trapa bicornis, Eliocharis tuberosa, and Ipomea obscura serve as the second intermediate hosts

Symptoms & Pathology

• Epigastric pain, nausea, and diarrhea are common, particularly in the morning
• Heavy infections can lead to generalized edema and ascites
• The fluke attaches to the intestinal mucosa, causing inflammation, ulceration, and abscesses
• Patients may experience generalized toxic and allergic reactions, leading to edema in various parts of the body

Diagnosis and Treatment

• Diagnosis is based on clinical symptoms in endemic areas
• Eggs are detected in feces (75 to 100 by 130 to 150 micrometers)

Fasciola hepatica and Fasciola gigantica (Sheep Liver Flukes)

• Fasciola hepatica is found in temperate regions
• Fasciola gigantica is found in tropical regions

Hosts and Geographic Location

• Lymnea philippinensis is the first intermediate host
• Watercress and grass are the second intermediate hosts
• Found worldwide, particularly in areas where livestock is raised and raw watercress is consumed
• Infections with Fasciola gigantica have been reported in Asia, Africa, and Hawaii

Infection and Diagnosis

• Transmission occurs through ingesting raw aquatic vegetation with encysted metacercaria
• Diagnosis involves detecting characteristic eggs in feces
• Sheep, cattle, and goats serve as reservoir hosts
• Adults measure 20-50x6-12 mm with a cephalic cone and branched intestinal ceca
• Ova are large, elliptical to oval, operculate, and light yellowish-brown and cannot be distinguished from F. buski

Clinical Features

• The acute phase is caused by the migration of the immature fluke in the hepatic parenchyma
• Abdominal pain, hepatomegaly, fever, vomiting, diarrhea, urticaria, and eosinophilia
• Chronic phase is caused by the adult fluke residing within the bile ducts
• Symptoms are more discrete and reflect intermittent biliary obstruction and inflammation
• Infections can occasionally occur in ectopic locations such as the intestinal wall, lungs, subcutaneous tissue, or pharyngeal mucosa

Diagnosis and Treatment

• Microscopic identification of eggs is useful in the chronic (adult) stage
• Eggs can be recovered in stools or in material obtained by duodenal or biliary drainage
• Antibody detection tests are useful in early invasive stages when eggs are not yet apparent in the stool or in ectopic fascioliasis
• False fascioliasis (pseudofascioliasis) refers to the presence of eggs in the stool
• This results from recent ingestion of infected livers containing eggs
• Unlike infections with other flukes, Fasciola hepatica infections may not respond to praziquantel
• Triclabendazole is the drug of choice, with bithionol as an alternative

Paragonimus westermani (Oriental Lung Fluke)

• Distributed in Japan, Korea, China, Philippines, and Southeast Asia
• Human transmission occurs through ingesting infected crustacea with metacercaria
• Diagnosis involves demonstrating characteristic eggs in feces or sputum
• "Chinese vase egg" describes eggs in feces or sputum

Identification

• Ova are oval, yellowish-brown with a flattened operculum resting on shoulders

Hosts

• Humans, wolves, foxes, tigers, leopards, cats, dogs, and monkeys are definitive hosts
• Freshwater snails, such as Antemelania asperata and Antemelania dactylus, are the first intermediate hosts
• Freshwater crayfish or crab (Sundathelphusa philippina-mountain crab) is the second intermediate host

Clinical Disease

• Light infections may be asymptomatic
• High eosinophilia is common
• Chronic cough and abundant mucus occur in heavy infections
• Hemoptysis is possible

Diagnosis & Treatment

• Ova detection in stool
• Ova detection in sputum (3% NaOH)
• Chest radiography
• The consumption of certain dishes like "Nam prik poo", "Drunken crab", "Kejang", "Ceviche", and "Kinagang, sinugba & kinilaw" is risky