Introduction to Trematodes

Lesson 9

Trematodes

Aka Flukes, platyhelminths

Platyhelminths

Dorsoventrally flattened helminths

Hermaphroditic forms

Intestinal, liver, and lung flukes

Blood flukes or schistosome

Separate sexes

Oral sucker

Through which the digestive system tract opens

Ventral sucker

Used for attachment

1 mm

Adult length (Metagonimus)

70 mm

Adult length Fasciola gigantic

Feces, Sputum, Urine

Eggs reach the environment by being passed in the?

Operculated eggs

Produced by hermaphroditic fluke;

Not embryonated

Non-operculated eggs

Produced by schistosomes;

contains a mature larva when passed

Larva

Aka Miracidia, Ciliated; capable of penetrating tissues of molluscan hosts; uses a particular species of snail as the first intermediate host

Cercariae

Free-swimming larvae, Results from a complex asexual multiplication process inside the snail, capable of penetrating human skin directly

Hermaphroditic flukes

Encyst on aquatic vegetation; Invade the tissues of second intermediate hosts (fish & crabs)

Metacercariae

Encysted larval stages, Results in human infection when ingested

tropical and subtropical regions

Where do human trematode infections commonly occur?

sporadic

how frequent are intestinal infections?How

Lack of sewage treatment,
Availability of appropriate intermediate hosts,
Dietary customs involving ingestion of infective metacercariae,
Increased use of irrigation in endemic areas

What factors contribute to the presence of human trematode infections?

Schistosomiasis

What parasitic disease is associated with increased use of irrigation in endemic areas?

Number of worms parasitizing the host,
Tissues and organs involved,
Host immune responses

What factors influence the clinical presentation of human trematode infections?

No, many infections are asymptomatic.

Are all human trematode infections symptomatic?

Recovery and identification of characteristic eggs in clinical specimens.

What is the primary method for diagnosing trematode infections?

Direct mounts

What lab technique is used for intermediate visualization of trematode eggs in stool?

Formalin-Ethyl Acetate Concentration Method.

Which method improves egg recovery in stool or sputum samples?

Zinc Sulfate Flotation Method.

What flotation method is used for detecting trematode eggs in urine but is less satisfactory?

Tissues

In which type of specimen are trematode eggs occasionally recovered aside from stool, sputum, or urine?

Fasciolopsis buski

An intestinal trematode; the largest species to infect humans.

China, Southeast Asia, and India.

Where is Fasciolopsis buski endemic?

Pigs

What is the natural reservoir of Fasciolopsis buski?

Metacercariae; transmission occurs via ingestion of aquatic food plants.

What is the infective form of Fasciolopsis buski and how is it transmitted?

Water chestnuts and water caltrop.

Common contaminated foods involved in Fasciolopsis buski transmission.

Wall of the duodenum and jejunum

Where does Fasciolopsis buski attach in the human body?

Approximately 3 months

How long does it take Fasciolopsis buski to mature into egg-laying adults?

Ulceration of the superficial mucosa

What kind of tissue damage does Fasciolopsis buski cause?

Diarrhea, epigastric pain, nausea, and eosinophilia.

What are common symptoms of Fasciolopsis buski infection?

Brown, oval, Thin-shelled, Inconspicuous Operculum, Unembryonated at excretion

Describe the ova (egg) characteristics of Fasciolopsis buski.

Stool microscopy for characteristic eggs

How is Fasciolopsis buski diagnosed?

Its eggs are morphologically indistinguishable from Fasciola spp. eggs.

Why is diagnosis of Fasciolopsis buski challenging?

Through geographic history and clinical symptoms.

How can Fasciolopsis buski be differentiated from Fasciola spp.?

Snail

Fasciolopsis buski First Intermediate host

Water plants

Fasciolopsis buski Second Intermediate host

Man

Fasciolopsis buski Definitive host

Minute intestinal trematodes measuring 1–3 mm in length.

What are Heterophyes and Metagonimus spp.?

Asia

Where are Heterophyes and Metagonimus infections commonly found?

Metacercariae

What is the infective form of Heterophyes and Metagonimus spp.?

Ingestion of metacercariae in raw or incompletely cooked freshwater fish.

How are Heterophyes and Metagonimus spp. transmitted to humans?

Diarrhea and abdominal pain

What are common symptoms of Heterophyes and Metagonimus infections?

Self-limited; worms have a lifespan of only a few months.

What is the usual course of infection for Heterophyes and Metagonimus?

Embryonated (contain developed miracidium);

Operculated shell

What are the ova characteristics of Heterophyes and Metagonimus?

Heterophyes & Metagonimus

has a Deeply seated operculum (similar to Opisthorchis)

Snail

Heterophyes and Metagonimus first intermediate host

Fish

Heterophyes and Metagonimus second intermediate host

Bird, fish eating mammals, humans

Heterophyes and Metagonimus Definitive host

Semisulcospira libertina

Metagonimus yokogawai 1st intermediate host

A small intestinal fluke measuring 0.8–1.1 mm

What type of parasite is Nanophyetus salmincola and how big is it?

Siberia and the Pacific Northwest Coast of the USA.

Where is Nanophyetus salmincola commonly found?

Metacercariae; transmitted through ingestion of raw, incompletely cooked, or home-smoked freshwater fish.

What is the infective form of Nanophyetus salmincola and how is it transmitted?

Salmon and trout

What types of fish commonly transmit Nanophyetus salmincola?

Abdominal pain, diarrhea, and eosinophilia

What are the symptoms of Nanophyetus salmincola infection in humans?

Broadly ovoid, Yellowish brown, Operculated, Thickened abopercular end

Describe the ova characteristics of Nanophyetus salmincola.

"Salmon-poisoning disease" caused by a rickettsial infection (highly lethal to dogs).

What disease is associated with Nanophyetus salmincola in canines?

Nanophyetus salmincola

What is the vector of the rickettsial infection causing salmon-poisoning disease in dogs?

A liver fluke (trematode).

What type of parasite is Fasciola hepatica?

Cattle, sheep, and goats.

What are the primary hosts of Fasciola hepatica?

Accidentally, by ingesting aquatic plants (e.g., watercress) contaminated with metacercariae.

How do humans become infected with Fasciola hepatica?

• Ingestion of metacercariae

• Larvae penetrate intestinal wall

• Migrate through peritoneal cavity to liver capsule

• Enter bile ducts and mature into adults

Describe the life cycle of Fasciola hepatica in humans.

snails

What is the intermediate host of Fasciola hepatica?

~2 months.

How long after infection do Fasciola hepatica begin laying eggs?

Painful inflammatory reaction, liver fibrosis, and bile duct damage.

What are the effects of larval migration through the liver?

Fibrosis, cholelithiasis (gallstones), and obstruction.

What are the pathological effects of adult Fasciola hepatica in the bile ducts?

Colic, Obstructive jaundice, Abdominal pain and tenderness, Cholelithiasis, Eosinophilia

What are clinical manifestations of Fasciola hepatica infection?

False infection due to ingestion of infected liver (e.g., from cattle or sheep); eggs appear in stool but no active infection.

What is a spurious infection of Fasciola hepatica?

Unembryonated, Oval, yellowish brown, Operculated, Indistinguishable from Fasciolopsis buski eggs

What are the ova (egg) characteristics of Fasciola hepatica?

Oriental liver fluke

What is the common name of Clonorchis sinensis?

Humans, piscivorous animals, cats, and dogs.

What are the primary hosts of Clonorchis sinensis?

China, Taiwan, Korea, Japan, and Vietnam.

In which regions is Clonorchis sinensis endemic?

Southeast Asia, especially Northern Thailand.

Where is Opisthorchis viverrini commonly found?

Europe

What is the geographic distribution of Opisthorchis felineus?

Amphimerus pseudofelineus.

What is another name for Opisthorchis guayaquilensis?

By ingesting metacercariae in raw or undercooked freshwater fish.

How are Clonorchis sinensis and Opisthorchis spp. transmitted?

Larvae migrate up the common bile duct into the liver bile ducts.

Describe the larval migration of Clonorchis/Opisthorchis in humans.

Up to 20 years

What is the lifespan of adult Clonorchis/Opisthorchis worms?

Up to 25 mm in length.

How large can adult Clonorchis/Opisthorchis worms grow?

Eggs are shed into the bile and passed in stools

How are the eggs of Clonorchis/Opisthorchis excreted?

Infections are often asymptomatic.

Are infections with Clonorchis sinensis and Opisthorchis often symptomatic?

Inflammation of the bile ducts, hyperplasia, fibrosis, and cirrhosis.

What happens when there are large numbers of Clonorchis sinensis and Opisthorchis flukes or repeated infections?

Cholangiocarcinoma (bile duct cancer).

What can longstanding infection with Clonorchis sinensis and Opisthorchis lead to?

Brown color with a prominent, seated operculum

What is the color and operculum characteristic of Clonorchis sinensis / Opisthorchis spp. eggs?

A small knob

What unique feature is found at the abopercular end of Clonorchis/Opisthorchis eggs?

Operculum and abopercular knob

What notable egg features are absent in Metagonimus spp.?

Paragonimus westermani,

Paragonimus mexicanus,

Paragonimus caliensis,

Paragonimus ecuadoriensis,

Paragonimus kellicotti

What are the Paragonimus spp. ?

Many areas of Asia

What are the regions where Paragonimus westermani is found?

Central and South America

What regions are Paragonimus mexicanus, caliensis, and ecuadoriensis found in?

North America

Where is Paragonimus kellicotti endemic?

Cats, dogs, other carnivores including humans.

What hosts are infected by Paragonimus species?

12 mm by 6 mm, found in pairs in the lung parenchyma, reside in fibrotic capsules.

Describe the adult Paragonimus worms.

yellow-brown shell, moderately thick, unembryonated, flattened operculum with prominent shoulders, thickened abopercular end (no knob).

Describe the ova of Paragonimus spp.

First: Snails

Second: Freshwater crabs or crayfish

What are the intermediate hosts in Paragonimus spp. life cycle (first and second)?

Ingestion of uncooked or marinated crustaceans (crabs/crayfish).

How are Paragonimus spp. transmitted to humans?

Released in the stomach → intestinal wall → peritoneal cavity → lungs via diaphragm

Describe the larval migration of Paragonimus.