Schistosomas (Blood Flukes)

• What type of organism are schistosomes?

  Blood flukes (trematodes)
• How do schistosomes differ from other trematodes?

  They have only one intermediate host
• What is the intermediate host for schistosomes?

  Freshwater snails
• How do schistosomes infect their hosts?

  Through direct penetration
• Who is the definitive host for schistosomes?

  Humans
• What is the diagnostic stage of schistosomes?

  Eggs in feces or urine
• What is the infective stage of schistosomes?

  Fork-tailed cercariae
• Where do schistosomes primarily inhabit?

  Blood vessels
• What type of eggs do schistosomes produce?

  Non-operculated
• What disease is caused by schistosomes?


  Schistosomiasis, Bilharziasis, and Snail/Swamp/Katayama Fever
• Which species of schistosomes are found in Asia and Africa?

  Schistosoma mekongi and Schistosoma intercalatum
• What is the significance of schistosomiasis in human health?

  Second most important parasitic disease
• How is schistosomiasis classified in terms of global health?

  One of the neglected tropical diseases
• What historical evidence exists for schistosomiasis?

  Found in mummies
• SCHISTOSOMES: LIFE CYCLE

  1.) Eggs are expelled from feces (Mansoni, Japonicum) or urine (Haematobium, Japonicum) into water.

  2.) Eggs hatch and release miracidia.

  3.) Miracidia penetrate snail IH.

  4.) Miracidia develops inside snail; released as free-swimming cercariae.

  5.) Fork-tailed cercariae penetrate definitive host.

  6.) After penetration, cercariae lose tails and become schistosomulae.

  7.) Schistosomulae migrate to portal blood in liver through circulation, where they mature into adults.

  8.) Paired adult worms migrate either to venules of bowel/rectum or venous plexus of bladder.