Clonorchis sinensis: Liver fluke

• Trematodes, or flukes, are unsegmented, flat helminths characterized by leaf or flat shapes.
• They possess prominent oral and ventral suckers.
• Trematodes are classified by habitat, including blood, liver, intestinal, and lung flukes.

Clonorchis sinensis

• Also known as the liver fluke.
• Human are definitive hosts, while dogs and fish-eating canines act as reservoir hosts.
• Snails are the first intermediate hosts and fish are the second.
• Exists in three stages: adult, eggs, and larval.
• Metacercariae is the infective stage.
• Primarily found in the biliary tract, and sometimes the pancreatic duct.
• Transmission occurs via consumption of undercooked freshwater fish containing larvae.
• Causes clonorchiasis, an inflammation of the biliary tract.
• Can be diagnosed by identifying eggs in stool samples.
• Praziquantel is an effective treatment.

Clonorchis sinensis Life Cycle

• Embryonic eggs are released into the bile ducts and subsequently the stool.
• Snails ingest the eggs, which then release miracidia.
• Miracidia undergo several developmental stages within the snail, transforming into cercariae.
• Cercariae are released from the snail and penetrate the flesh of freshwater fish, becoming metacercariae.
• Humans become infected when they ingest undercooked, salted, pickled, or smoked freshwater fish.
• Once ingested, metacercariae mature in the duodenum and biliary tract within approximately one month.
• Adult flukes reside in the small and medium-sized bile ducts.

Paragonimus westermani

• Known as the lung fluke due to its presence in the respiratory tract.
• Human definitive hosts.
• Freshwater snails serve as the first intermediate hosts, and freshwater crabs or crayfish act as second intermediate hosts.
• Exists as adult, eggs, and larvae.
• Metacercariae within contaminated crab or crayfish is the infective stage.
• Resides in the respiratory tract.
• Acquired through consumption of undercooked crab or crayfish that contain metacercarial larvae.
• Causes paragonimiasis, characterized by lung inflammation and secondary bacterial infections.
• Presence of eggs in sputum and feces is diagnostic.
• Treated effectively with Praziquantel.

Paragonimus westermani Life Cycle

• Eggs are excreted in sputum or feces into the environment.
• Eggs embryonate and hatch into miracidia.
• Snails ingest miracidia which then undergo several developmental stages inside the snail.
• Cercariae emerge from the snail and invade crabs or crayfish, where they encyst and develop into metacercariae.
• Humans become infected by consuming inadequately cooked or pickled crab or crayfish.
• In the duodenum, metacercariae excyst, penetrate the intestinal wall, and migrate through the abdominal cavity and diaphragm into the lungs, where they encapsulate and mature.
• Worms can reach other organs like the brain and striated muscles, but cannot complete their lifecycle in those sites.
• Infections can persist for up to 20 years.
• Other animals that can harbor Paragonimus include pigs, dogs, and feline species.