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

Introduction of Schistosoma mansoni

Schistosoma mansoni is a major blood fluke which is also known as Mansons’ blood fluke. It is the causative agent of intestinal schistosomiasis or bilharziasis in humans.

The characteristics of Schistosoma include:

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

• 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 mansoni

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Trematoda

Order: Diplostomida

Family: Schistosomatidae

Genus: Schistosoma

Species: S. mansoni

History of Schistosoma mansoni

Schistosoma mansoni was first demonstrated in 1851 by Bilharz- the lateral spined eggs in the female schistosomes were obtained from an autopsy from Cairo. Manson in 1903 demonstrated the eggs in the feces of patients without haematuria.

In 1907 Sambon named the parasite Schistosoma mansoni, including schistosomes producing lateral-spined eggs.

Habitat of Schistosoma mansoni

Both male and female Schistosoma mansoni are found together in the mesenteric venules which drain the large intestine and posterior part of the ileum (small intestine). Occasionally, they can be found in the branches of the superior mesenteric vein and vesical plexus.

Morphology of Schistosoma mansoni

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

Adult

• the body is covered with integument which protects the fluke from the immune system of the host

• 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 100-300 terminal-spined eggs per day

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

• the body surface of the male is finely tuberculate

• in males, the number of testes varies from 6 to 9 and is arranged in a cluster

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

• about 1-4 eggs are present in the uterus

• does not multiply in man

Egg

• measures 114μm to 175μm in length and 40μm to 70μm in breadth

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

• identifying feature of Schistosoma mansoni egg is a lateral spine near the rounded posterior end

• the sharp lateral spine measures 20μm in length

• eggs are fully embryonated when laid

• Schistosoma mansoni eggs are short-lived and infectious to snails only

Infective form

Cercaria

• the infective form of Schistosoma mansoni

• elongated oval body with fork-tail

• measures 185μm to 230 μm in length and 75 μm to 110 μm in breadth

• 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

• basophilic in nature with two pairs of cephalic glands