Trematodes: Flukes Overview

Trematodes Overview

• Trematodes belong to the Class Trematoda and Phylum Platyhelminthes
• They are commonly known as flukes
• Most flukes are hermaphroditic (monoecious) and capable of self-fertilization, except for Schistosoma species.

Types of Flukes

• Intestinal flukes: Flat and leaf-shaped.
• Liver flukes: Flat and leaf-shaped.
• Lung flukes: Flat and leaf-shaped.
• Blood flukes: Cylindrical body shape (Schistosoma sp.).

Trematode Body

• Covered by a cuticle that can be spiny or smooth
• Possess 2 suckers for attachment: an anterior oral sucker and a ventral sucker (acetabulum).
• They have excretory, neuromuscular, digestive, and reproductive systems.
• They lack circulatory and respiratory systems.
• They possess a single ovary and 2 testes.
• The uterus, housing eggs, is the largest organ.

General Life Cycle of Trematodes

• Complex life cycle involving multiple hosts
• Humans serve as the definitive host.
• Eggs exit the host via feces, urine, or sputum.
• The intermediate host is typically a freshwater snail.
• Larval stage: Ciliated miracidium, which undergoes asexual multiplication in the snail.
• Cercaria is the final larval stage, motile and capable of skin penetration in humans.
• Metacercariae encyst on aquatic vegetation or within a second intermediate host (freshwater fish or crustacean).

Fasciolopsis buski

• Common name: Large intestinal fluke
• Intermediate host: Snail
• Infective stage: Metacercariae
• Transmission: Ingestion of infected aquatic plants
• Definitive hosts: Humans and pigs
• Habitat in humans: Small intestines, reaching up to 7.0 x 1.5 cm in size.
• Diagnostic stage: Unembryonated eggs in feces.

Fasciolopsis buski Characteristics

• Adult worms appear fleshy, dark red, and elongate-ovoid without a cephalic cone.
• Eggs are yellowish-brown with a clear, thin shell, featuring a small operculum but lacking opercular shoulders.
• Immature eggs have less defined operculum "breaks" in the shell outline making the visualization difficult.

Clinical Disease: Fasciolopsiasis

• Light infections: Adults reside in the duodenum and jejunum.
• Heavy infections: Adults populate the stomach and most of the intestinal tract, inducing traumatic, obstructive, and toxic effects.
• Attachment of worms leads to local inflammation, mucus hypersecretion, hemorrhage, ulceration, and potential abscess formation.
• Heavy infections can cause bowel obstruction, edema, ascites, impaired vitamin B12 absorption, marked eosinophilia, and leukocytosis.
• Profuse and yellow-green stool, malabsorption and severe cachexia, prostration
• Symptoms may resemble giardiasis, peptic ulcer, or other causes of bowel obstruction.
• Depending on the worm burden, severe conditions may arise, including cachexia, prostration and potentially death.

Fasciolopsiasis Diagnosis

• Eggs are found in the stool, with adult worms rarely detected during heavy infections.
• Passed eggs do not contain mature larvae but undifferentiated embryos.
• Formalin-ethyl acetate sedimentation concentration is advised for egg retrieval.
• Less mature eggs pose challenges in visualizing the operculum, and eggs lack opercular shoulders.

Fasciolopsiasis Treatment and Prevention

• Praziquantel is the drug of choice.
• Niclosamide is an alternative drug.
• Thoroughly cook all aquatic plants before consumption.
• In endemic areas, prevent fecal contamination from humans or pigs where aquatic plants grow and avoid feeding raw aquatic plants to pigs.

Fasciola hepatica

• Common name: Common liver fluke or sheep liver fluke
• Intermediate host: Snail
• Infective stage: Metacercariae
• Transmission: Ingestion of infected aquatic plants
• Definitive hosts: Humans and sheep
• Habitat in humans: Small intestines
• Diagnostic stage: Unembryonated eggs

Fasciola hepatica Characteristics

• Eggs are identical to those of F. buski.
• Both eggs have an oblong undeveloped miracidium with a distinct operculum, referred to as "popping operculum".
• Adults are comparable in size to F. buski.
• Unlike F. buski, F. hepatica has distinct "shoulders"

Laboratory Diagnosis

• The preferred specimen is stool
• Take into account patient symptoms and travel history.
• Speciation involves the recovery of the adult worm.
• Other methodologies include Enterotest, ELISA, and gel diffusion.

Fascioliasis: Sheep Liver Rot Symptoms

• Symptoms arise from the physical presence and attachment of the adult worm within the biliary tract.
• Symptoms: headache, fever, chills, liver area pains, eosinophilia, jaundice, liver tenderness, anemia, diarrhea, and digestive discomfort.
• Biliary obstruction may occur

Halzoun Syndrome

• An acute hypersensitivity syndrome affecting the buccopharyngeal mucosa and upper respiratory tract.
• This syndrome results from ingestion of raw or undercooked sheep/goat liver.
• Temporary pharyngeal attachment of larvae occurs.

Fasciola hepatica Treatment and Prevention

• Dichlorophenol (bithionol) is the recommended treatment
• Promote proper human fecal disposal and sanitation, particularly in areas with animal reservoir hosts.
• Manage the snail population.
• Avoid consuming raw water plants or contaminated water.

Clonorchis sinensis

• Common name: Chinese or oriental liver fluke
• The first intermediate host: Snail
• The second intermediate host: Freshwater fish
• Infective stage: Metacercariae
• Mode of transmission: the ingestion of infected raw or undercooked fish
• The definitive host: Man
• Habitat of adults in man: biliary ducts
• Diagnostic stage: embryonated eggs (intermittent passage)

Clonorchis sinensis Morphology

• Egg size is 30 by 15 µm
• Developed miracidium
• Distinct operculum opposite to a small knob
• Thick rim is seen around the operculum, also known as "shoulders"

Clonorchis sinensis Adult Morphology

• Size is 2 by 0.5 cm
• Each end is narrower than the midportion of the body

Clonorchis sinensis Diagnosis

• They can inhabit bile ducts for 20-25 years
• At the early stage of the infection, therw are no obvious clinical symptoms
• misdiagnosed due to its nonspecific symptoms - fatigue, inappetence, nausea, bellyache, jaundice, and hepatosplenomegaly
• By stool examination (Sequential Fecalysis); a direct fecal smear, a Kato-Katz method, formalin-ether concentration technique (FECT)
• Also serological methods and DNA-based methods
• Diagnosis with Imaging methods - ultrasound, computer tomography (CT), magnetic resonance imaging (MRI) and tissue harmonic imaging (THI)

Clonorchiasis

• Most prevalent in middle to low income countries.
• Infections can be mild, where no obvious symptoms present.
• Heavily effected can result in fever, abdominal pain, eosinophilia, diarrhea, anorexia, epigastric discomfort, and occasional jaundice
• Enlargement and tenderness of the liver and leukocytosis

Clonorchiasis Treatment and Prevention

• Treatment done with praziquantel or albendazole
• prevention: Avoiding eating raw or undercooked freshwater fish, cooking the fish adequately (internal temperature >63 °C), freezing (≤
• 20 °C for 7 days; ≤ -35 °C for 15 h)
• Food safety practices

Heterophyes heterophyes and Metagonimus yokogawai

• Metacercariae excyst in the small intestine.
• Fish-eating mammals and birds can be infected as well.
• The adult resides in the small intestine
• Embryonated eggs with a fully-developed miracidium are passed in feces

Heterophyes heterophyes and Metagonimus yokogawai: Eggs

• Indistinguishable and may be easily confused with those of Clonorchis.
• Measuring 30 by 15 μm.
• Have shoulders but less distinct than those of Clonorchis
• May lack the small terminal knob and exhibit an operculum
• Heterophyes eggs typically have a much thicker shell than those of Metagonimus.

Heterophyes heterophyes and Metagonimus yokogawai: Adult Forms

• Heterophyes adult is small, over 1.0 by 0.5 mm in size
• Pyriform, grayish, outer layer of fine spines scaly in appearance

Metagonimus

• 1.5 by 0.5 mm
• Pyriform, a tiny layer of scaly spines heavily distributed over the anterior end

Heterophyiasis/Metagonimiasis

• Light infections are asymptomatic, heavy infections: abdominal pain and discomfort chronic mucous diarrhea & eosinophilia
• The eggs escape into the lymphatics or venules via intestinal wall penetration and migrate to other areas of the body leading to granulomas

Heterophyiasis/Metagonimiasis: Treatment, prevention, and control

• Treatment: praziquantel
• Prevention: avoiding consuming undercooked fish, practicing proper fecal disposal & control of snails

Paragonimus westermani

• Common name: Oriental lung fluke
• 1st intermediate host snail
• 2nd intermediate host crustaceans
• Infective stage: metacercariae
• Mode of transmission: ingestion of infected crustaceans
• Definitive host: man
• Habitat of adults in man: cystic cavities in lungs
• Diagnostic stage: unembryonated eggs

Paragonimus westermani: Eggs

• Size is 80-120 µm long by 45-70 µm wide
• Yellow-brown, ovoid or elongate, with a thick shell
• Often asymmetrical with one end slightly flattened
• At the large end is a clearly visible operculum that's opposite (abopercular) end

Paragonimus westermani: Adult

• Large, robust, ovoid flukes
• Hermaphroditic
• Cuticle possesses spines, similar to the other adult trematodes

Paragonimus westermani: Laboratory diagnosis

• Stool examination - demonstration of eggs; but not present until 2 to 3 months after infection
• Effusion fluid or biopsy material - eggs may also be encountered
• Radiographic Examination: Patchy infiltrates with cystic shadow/calcification May mimic Tb, chronic bronchitis, fibrosis
• Antibody detection

Paragonimiasis Prevalence

• Prevalent in Asia, Africa, and Central and South America.

Paragonimiasis: Acute Stage

• Acute stage corresponds to invasion and migration of young flukes

Paragonimiasis: Chronic Stage

• Corresponds to the adult flukes residing in a cyst in the lung parenchyma
• Chronic cough with gelatinous, tenacious rusty-brown sputum
• Most important form of extrapulmonary paragonimiasis

Paragonimiasis: Treatment

• Praziquantel is the medication of choice alternative drug - bithionol

Paragonimiasis: Prevention and Control

• Avoiding human ingestion of undercooked crayfish and crabs
• Exercising proper disposal of human waste products

Schistosoma sp.

• Intermediate host: snail
• Infective stage: cercariae
• Mode of transmission: skin penetration
• Definitive host: man
• Diagnostic stage: eggs

Schistosoma sp. Characteristics

• Female: 2 cm long; male: 1.5 cm long
• Male surrounds the female almost completely, facilitating copulation

Schistosoma: Laboratory diagnosis

• Detection of eggs stool/urine specimens
• Rectal Biopsy
• Serologic tests - detect antibodies and/or antigens in blood/urine

Schistomiasis

• Schistosome eggs induce the morbidity caused by schistosome infections
• Eggs become permanently lodged in intestines/livers/bladder/urogenital system & granuloma formation can occur

Katayama syndrome: Acute schistosomiasis

• A sudden onset that involves fever, malaise, myalgia, headache, eosinophilia, fatigue, and abdominal pain lasting 2-10 weeks

Intestinal schistosomiasis (chronic)

• Consists of non-specific intermittent abdominal pain, diarrhea, and rectal bleeding
• Upper abdominal discomfort with palpable nodular
• Hard hepatomegaly, often with splenomegaly Pulmonary hypertension

Urogenital schistosomiasis

• Hematuria
• Squamous-cell carcinoma of the bladder

Treatment

• Praziquantel: main drug
• Artemisinin derivatives: kill immature larval forms

Schistomiasis Prevention

• Preventive chemotherapy
• Snail control
• Behavioral modification
• Water and sanitation improvements