Pathogenesis (development of disease)
The disease is mainly caused by five human pathogenic trematodes: Schistosoma (S.) haematobium, S. mansoni, S. japonicum, S. intercalatum, and S. mekongi.
Pathogen reservoir are snails as intermediate hosts in fresh waters (rivers, lakes), from which schistosoma larvae, so-called cercariae, are released.
Transmission occurs percutaneously (through the skin) in water. The parasites penetrated in this way reach the liver via the blood and lymph. There they develop into adult worms (6-20-(26) mm long) in the liver sinusoids after weeks. These migrate retrogradely into the venous plexuses of the intestine and bladder to lay eggs.
The adult worms lay about 3,000 worm eggs daily during their multi-year life, which lead to an inflammatory response with granuloma formation, especially in the liver, urinary bladder, and rectum.
Contamination of fresh water with feces containing worm eggs causes these larvae to hatch into so-called mirazids. These develop into fork-tailed larvae, known as cercariae, when they reach certain snails, which are their intermediate hosts. The cercariae, in turn, can swarm out in the water and penetrate percutaneously when they come into contact with human skin.
Infection with Schistosoma haematobium results in urogenital schistosomiasis (bladder schistosomiasis) and the other causative agents (S. mansoni, S. intercalatum, S. japonicum, S. mekongi) result in intestinal or gut schistomiasis.
Etiology (causes)
Schistosoma [schistosomiasis; schistosomiasis]
- Transmission in water percutaneously (through the skin).