Parasitology Training Manual

The Schistosomes

• The Schistosoma species contain the largest ova of a parasite infecting humans.
• Blood flukes
• Unlike other trematodes they exist in both male and female sexes.
• Most trematodes are long and flat. The Schistosomes are long and narrow.
• The Schistosoma species we will study here are listed below.
• The World Health Organization has stated that of the six most devastating diseases to infect man five are caused by parasites. Schistosomiasis is one of those parasites.(15)

Schistosoma mansoni
Schistosoma haematobium
Schistosoma japonicum
Schistosome dermatitis (Swimmer's Itch)

Schistosoma species Life Cycle

With the female lying in the gynecophoric canal of the male she lays 300 - 3500 eggs daily(depending on the species). A miracidium develops within the egg. The egg is released into the tissues surrounding the intestine or bladder. The egg then makes its way into the intestine or bladder and is passed with feces or urine. The miracidium hatches and penetrates a suitable snail to further develop and emerge as a cercariae. Upon contact with a human these cercariae penetrate the skin or mucous membranes and migrate via the blood to the heart and lungs, through the portal vessels to the liver where they mature. 20 days after exposure the worms migrate to the mesenteric, vesical and pelvic venules and begin to pass eggs 7 - 30 days later.

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