Trematodes and Flukes

• Trematodes are leaf or flatly shaped, earning them the name "flukes"
• Trematodes are unsegmented, flat, and broad
• They feature large, prominent suckers, known as oral and ventral suckers

Life Cycle of Clonorchis sinensis

• Embryonic eggs are released into the bile and stool.
• Eggs are consumed by snails, the intermediate host.
• In the snail, eggs release miracidia that go through developmental stages and become cercariae.
• Cercariae are released and penetrate freshwater fish, becoming metacercariae.
• Humans get infected by eating undercooked, salted, pickled, or smoked freshwater fish.
• Metacercariae mature in the duodenum and biliary tract in about a month.
• Adult flukes live in small and medium-sized bile ducts.

Life Cycle of Paragonimus westermani

• Eggs are excreted in sputum or feces into the environment.
• Eggs become embryonated and hatch into miracidia.
• Snails are the first intermediate host, larvae undergo developmental stages here.
• Cercariae emerge from the snail, invade crabs or crayfish, and encyst into metacercariae.
• Mammalian hosts get infected via metacercariae in crabs or crayfish.
• Humans become infected by eating undercooked or pickled crab or crayfish.
• Metacercariae excyst in the duodenum, penetrate the intestinal wall, move through the abdominal cavity, pass through the diaphragm, and reach the lungs, where they become encapsulated and mature.
• Adult worms can reach other organs like the brain and striated muscles, but the life cycle cannot be completed in these locations.
• Infections can last up to 20 years in humans.
• Animals like pigs, dogs, and felines can also host Paragonimus spp.

Clonorchis sinensis

• Clonorchis sinensis, or the liver fluke, infects humans (definitive hosts) and fish-eating canines (reservoir hosts).
• Snails act as the first intermediate host, and fish act as the second intermediate host.
• The parasite exists in three stages: adult, egg, and larval.
• The infective stage is the metacercaria (larva stage).
• Transmission occurs through consuming undercooked freshwater fish containing larvae.
• Present in the biliary tract and sometimes the pancreatic duct.
• Clonorchis sinensis causes clonorchiasis, leading to inflammation of the biliary tract.
• Clonorchis sinensis is diagnosed by observing eggs in the stool.
• Clonorchis sinensis is treated with praziquantel.

Paragonimus westermani

• Paragonimus westermani, or the lung fluke, is found in the respiratory tract.
• Paragonimus westermani causes paragonimiasis, resulting in inflammation and secondary bacterial infection of the lungs.
• Humans serve as definitive hosts, freshwater snails are the first intermediate hosts, and freshwater crabs or crayfish are the secondary intermediate hosts.
• Transmission happens by consuming undercooked crab or crayfish containing metacercarial larvae (infective stage).
• Both Paragonimus westermani and Clonorchis sinensis are diagnosed by observing eggs in the stool.
• Both Paragonimus westermani and Clonorchis sinensis are treated with praziquantel.