Life Cycle
The excretion Schistosome eggs in urine or feces depending on species
The hatching of the eggs leading to release of the free-swimming, ciliated larvae called miracidia
Miracidia find and penetrate the snails, which are the intermediate hosts (specific species of snails is dependent on the species of schistosoma)
Within the snails, two successive generations of sporocysts occur
Sporocyts gives rise to the infective free-swimming larvae with forked tails called cercariae, and they leave the snails to enter the water
Cercariae finds the human hosts and penetrate their skin
Upon entrance into the human hosts, cercariae lose their tails and become schistosomulae
The schistosomulae travels to the lungs and heart via the venous circulation
They migrate to the portal venous system of the liver where they mature into the adult form with two separate sexes
The adult male and female are paired together, exits the liver via portal venous system, and travel to the venous systems of the intestines or bladder (species dependent) and produce eggs
S. japonicum - superior mesenteric veins (but can also inhabit inferior mesenteric veins)
S. mansoni - inferior mesenteric veins (but can also inhabit superior mesenteric veins)
S. haematobium - vesicular and pelvic venous plexus of the bladder (occasionally rectal venules)
S. intercalatum and S. guineensis - inferior mesenteric plexus (lower portion of the bowels compared to S. mansoni)Schistosomes can live an average of 3–5 years, and the eggs can survive for more than 30 years after infection. Other hosts
Schistosomiasis is also a concern of cattle husbandry and mice. O-methyl-threonine is weakly effective in mouse schistosomiasis but is not in use.
The examination can be performed on a simple smear (1 to 2 mg of fecal material). Because eggs may be passed intermittently or in small numbers, their detection is enhanced by repeated examinations or concentration procedures, or both. In addition, for field surveys and investigational purposes, the egg output can be quantified by using the Kato-Katz technique (20 to 50 mg of fecal material) or the Ritchie technique. Eggs can be found in the urine in infections with S. haematobium (recommended time for collection: between noon and 3 PM) and with S. japonicum. Quantification is possible by using filtration through a nucleopore filter membrane of a standard volume of urine followed by egg counts on the membrane. Tissue biopsy (rectal biopsy for all species and biopsy of the bladder for S. haematobium) may demonstrate eggs when stool or urine examinations are negative.Identification of microhematuria in urine using urine reagent strips is more accurate than circulating antigen tests in the identification of active schistosomiasis in endemic areas. Antibody detection
Antibody detection can be useful to indicate schistosome infection in people who have traveled to areas where schistosomiasis is common and in whom eggs cannot be demonstrated in fecal or urine specimens.