Schistosoma japonicum - Introduction, Classification, History, Habitat, Morphology

Introduction of Schistosoma japonicum

Schistosoma japonicum is the most pathogenic Schistosoma which is the causative agent of schistosomiasis japonica or oriental schistosomiasis.

The characteristics of Schistosoma include:

• unisexual (diecious) – fertilization takes place in the host liver

• in males, the number of testes varies from 4 to 8

• in females, Laurer’s canal is absent

• eggs are non-operculate, fully embryonated when laid

• cercariae are pharyngeal cause infections in the host by penetration through unbroken skin

• muscular pharynx and the encysted metacercarial stage is absent

Classification of Schistosoma japonicum

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Trematoda

Order: Diplostomida

Family: Schistosomatidae

Genus: Schistosoma

Species: S. japonicum

History of Schistosoma japonicum

The history of the discovery of Schistosomiasis japonicum began in the 18th century in Japan. It was first described in 1847 in Japan by physician Fuji. The eggs of the parasite were demonstrated in the human feces by Fujinami in 1904 while the adult form of the parasite was first described by Katsurada the same year. Katsurada had discovered the adults in dogs and cats and was the one who ascribed the name japonicum.

The life cycle of Schistosoma japonicum was described in 1912/13 by Miyagawa.

Habitat of Schistosoma japonicum

The Schistosoma japonicum habitats the mesenteric venules of the small intestine and the rectal (haemorrhoidal) plexus of veins.

Morphology of Schistosoma japonicum

Among the morphological forms of Schistosoma japonicum, the adult, egg, and cercaria are the important forms.

Adult Form

• the adult form of the parasite is covered with integument which protects the fluke from the immune system of the host

• Schistosoma japonicum lacks tuberculate-like-projections on surfaces of the integument

• unisexual (diecious) – male holds female in the gynecophoral canal

• the male is short and stout (1cm-1.5cm in length and 0.9mm in breadth)

• female is 2cm in length and 0.25mm in breadth

• the female can lay around 500-3500 central spined eggs per day – which is 10 times more than S. mansoni or S. haematobium

  * eggs containing miracidia extrude through the mucosa, submucosa, and into the intestinal lumen

• the life span of an adult is 20 years while in man, it lives for 5-6 years

• in males, the number of testes is 7 and arranged in linear series

• the ovary is positioned in the posterior to middle of the female body

• about 50-300 eggs are present in the uterus

• does not multiply in man

Egg

• measures 70 μm to 100 μm in length and 55 μm to 65 μm in breadth

• subspherical, oval-shaped, yellowish brown and non-operculated

• identifying feature of Schistosoma japonicum egg is a central spine in a depression on the shell so is not easily visible

• eggs are fully embryonated when laid

• Schistosoma mansoni eggs are infectious to snails only

Infective form

Cercaria

• the infective form of Schistosoma japonicum

• elongated oval body with fork-tail

• measures 100 μm to 160 μm in length, 40 μm to 60 μm in diameter, and the trunk measures 140 μm to 160 μm by 20 μm to 35 μm

• has two suckers and a bifurcated elongated tail measuring 100 μm in length

• the entire body is covered with extremely spine-like projections

• short-lived- lives only 24 hours to 72 hours

• male and female cercaria are morphologically similar to other Schistosoma species

• oxophilic in nature with four pairs of cephalic glands