Schistosomiasis Flashcards
What is Schistosomiasis?
It is a parasitic disease caused by trematodes (blood flukes) of the genus Schistosoma
What is another name for Schistosomiasis?
Bilharziasis
What are the primary species of Schistosoma that affect humans?
- Schistosoma haematobium (causes urogenital schistosomiasis)
- Schistosoma mansoni (causes intestinal schistosomiasis)
- Schistosoma japonicum (causes intestinal schistosomiasis)
Describe the life cycle of Schistosoma
- Eggs shed from infected humans
- Eggs hatch and release miracidia
- Miracidia infect the intermediate hosts, fresh water snails
- Snails release cercariae into water bodies
- Cercariae penetrate human skin in contact with contaminated water
- Cercariae turn into schistosomula in the bloodstream
- Schistosomula migrate to the liver where they mature into adult worms and pair
- Paired worms migrate to the mesenteric or pelvic veins where the females lay eggs
- Eggs are excreted into the urine and faeces into freshwater and the cycle continues.
Schistosoma eggs hatch into what?
Miracidia
Miracidia become what in the infected freshwater snail?
Cercariae
Cercariae become what in the bloodstream of infected humans
Schistosomula
What are the classes of antischistosomal agents?
- Antimonials
- Thioxanthones
- Nitrothiazoles
Give examples of drugs in the antimonial class
- Antimony sodium gluconate
- Antimony potassium tartrate
Give examples of drugs in the thioxanthone class
Lucanthone
Give examples of drugs in the nitrothiazole class
Niridazole
Write four characteristics of Praziquantel that make it a suitable antischistosomal agent
- It is effective against all major species of schistosoma
- It is well absorbed orally
- It is metabolised in the liver
- It has a short half-life
What is the MOA of praziquantel?
Praziquantel induces rapid contractions in the schistosome muscles by increasing permeability to calcium (that is causing influx of calcium) leading to paralysis and death.
Oxamniquine is effective against what species of schistosoma?
S. mansoni
What is the MOA of oxamniquine?
Oxamniquine is converted to an active ester which binds to schistosoma DNA causing irreversible inhibition of nucleic acid synthesis leading to death.
