Schistosomiasis (bilharziasis) is caused by the parasitic infection Schistosoma (the main pathogenic species for humans are Schistosoma mansoni, Schistosoma japonicum, and Schistosoma haematobium) are trematode worms of the genus.

Schistosomiasis is endemic in Africa, South America, and Asia: about 200 million people are infected, and about 600 million are at risk.

How schistosomiasis is transmitted

Life Cycle

lifecycle

Sourced from the CDC website

Schistosoma eggs are eliminated with feces or urine, depending on the species image. Under appropriate conditions, the eggs hatch and release miracidia image, which swim and penetrate specific snails, intermediate hosts image. The stages in the snail include two generations of sporocysts image and the production of cercariae image. Upon release from the snail, the infective cercariae swim, penetrate the human host’s skin image, and shed their forked tails, becoming schistosomulaimage. The schistosomulae migrate via venous circulation to the lungs, then to the heart, and then develop in the liver, exiting the liver via the portal vein system when matureimage image; male and female adult worms copulate and reside in the mesenteric venules, the location of which varies by species (with some exceptions) image. For instance, S. japonicum is more frequently found in the superior mesenteric veins draining the small intestine image, and S. mansoni occurs more often in the inferior mesenteric veins draining the large intestine image. However, both species can occupy either location and are capable of moving between sites. S. intercalatum and S. guineensis also inhabit the inferior mesenteric plexus but are lower in the bowel than S. mansoniS. haematobium most often inhabits the vesicular and pelvic venous plexus of the bladder image, but it can also be found in the rectal venules. The females (size ranges from 7–28 mm, depending on species) deposit eggs in the small venules of the portal and perivesical systems. The eggs are moved progressively toward the lumen of the intestine (S. mansoni, S. japonicum, S. mekongi, S. intercalatum/guineensis) and the bladder and ureters (S. haematobium). They are eliminated through feces or urine image.

How it manifests itself

Schistosomiasis may run entirely asymptomatically or manifest itself with an allergic reaction to the presence of the parasites (fever, itching, abdominal pain, nausea), burning on urination, and the presence of blood in the urine.

In the case of chronic infection, gastrointestinal, liver, lung, and bladder complications may occur.

Long-term invasion of the urinary tract can cause terminal kidney damage, while in some cases, a bladder infection is related to bladder cancer.

Diagnosis is made by searching for the parasite’s eggs in feces and urine.

Schistosomiasis is treated with antibiotic therapy, but there is no vaccination.

Prophylaxis advises against bathing in rivers, lakes, and canals in risk areas; one should also avoid, for example, showering or washing with water collected from contaminated sources.

On the other hand, bathing in the sea or swimming pools where the water is purified is safe.

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