Chronic and advanced schistosomiasis

Chronic and advanced disease is caused by mature, patent, schistosome infections (1).

Eggs which are not excreted usually become permanently lodged in the intestines or liver (for S mansoni, S japonicum, and S mekongi) or in the bladder and urogenital system (for S haematobium)

• these eggs cause a granulomatous host immune response which in turn induces chronic inflammation that leads to the disease manifestations of schistosomiasis (1,2)

Parasites require to expel its ova to the external environment for species survival, hence the worms lay their eggs as near as possible to the exterior environment:

• in the urinary bladder - Schistosoma haematobium
• in the distal colon and rectum - Schistosoma mansoni, S. japonicum, Schistosoma intercalatum and Schistosoma mekongi

These sites are considered as "primary targets" while lesions may spell over into "secondary targets" by different mechanisms e.g. - upper urinary tract may be involved as a result of obstruction or reflux at the uretero-vesical junctions (2).

Reference:

1. Gray DJ et al. Diagnosis and management of schistosomiasis. BMJ. 2011;342:d2651.
2. Barsoum RS, Esmat G, El-Baz T. Human schistosomiasis: clinical perspective: review. J Adv Res. 2013;4(5):433-44.