Trematodes - Classification, Definition

Trematodes


What are Trematodes / Definition

The trematodes are commonly known as flukes. The species are parasitic to man, belonging to the subclass - Digenea(Digenetic trematodes). They are hermaphrodites except for the Schistosoma which is unisexual. The mouth of the trematodes is surrounded by the anterior or oral sucker. They are divided into three sub-orders: namely Strigeata, Distomata, and Amphistomata.



What is the classification of Trematodes according to the habitat of Trematodes?

1) Intestinal Trematodes (Intestinal flukes)

a) Small Intestine - 

Fasciolopsis buski - Present in the small intestine of man and pig. The normal host is a pig.
Heterophyes heterophyes - Present in cat, dog, wolf, fox, and man.
Metagonimus yokogawai - Present in man, pig, cat, and pelican.
Watsonius watsoni - The normal host is a monkey.

b) Large Intestine - 

Gastrodiscoides hominis - Common flukes in Bengal and Assam. Pig is the common reservoir.


2) Hepatic Trematodes (Liver flukes)

a) Fasciola hepatica - Present in herbivores animals like sheep, goats, and cattle. It lives in the biliary passages of the liver.

b) Clonorchis Sinensis - It is a common parasite of dogs, cats, pigs, rats, and men. The adult worm lives in the biliary tract of the liver.

c) Opisthorchis felineus - Common parasite of cats, dogs, foxes, and pigs. The parasite lies in the biliary and pancreatic passage of the host.


3) Lung Trematodes (Lung flukes)

Paragonimus westermani - The adult worm lives in the respiratory tract of the man.


4) Blood Trematodes (Blood flukes)

a) In vesical plexus (mesenteric branch of the portal vein)e.g., Schistosoma haematobium. The adult worm lives in the pelvic venous plexus like vesical, prostatic, and uterine plexus of veins.

b)In the rectal venous plexus and portal venous system.
  1. Schistosoma mansoni - The adult worm lives in the mesenteric veins of the sigmoidal-rectal area and also in the branches of the portal vein in the liver.
  2. Schistosoma Japonicum - The worm lives in the intra-hepatic portion of the portal venous system, mesenteric veins draining the ileocaecal region and rectal plexus of veins.

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