The Biology of Schistosomiasis

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The Biology of Schistosomiasis

• By Tricia Stone, Marielle Remillard Tracy
  Wright

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Schistosomes

• macroscopic parasite from the genus Schistosoma
• characterized by significant sexual dimorphism
• Schistosomasplit body

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Types of Schistosomes

• Three species affect humans
• 1.) S. mansoni large intestine
• 2.) S. japonicum small intestine
• 3.) S. haematobium urinary bladder

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Life Cycle
intermediate fresh water snail host
miracidia
feces and urine
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Intermediate Snail Hosts

• S. mansoni Biomphalaria (Africa)
• S. haematobium Bulinus (Africa)
• S. japonicum Oncomelania (Asia)

Biomphalaria
Bulinus
Oncomelania
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Life Cycle
intermediate fresh water snail host
cercariae
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Life Cycle in the Human
cercariae
human host
human host
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Life Cycle in the Human
schistosomulum
human host
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Life Cycle in the Human
schistosomulum
human host
adult schistosome
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Life Cycle in the Human
eggs
excreted in the feces and urine
adult schistosome
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Life Cycle
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Stage 1 Migratory Phase

• moves through the body to target tissue
• begins with penetration through egg production
• often symptomless
• possible rash and itchy skin
• some upper respiratory complications (i.e. cough)

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Stage 2 Acute Phase

• 4-10 weeks after infection
• begins with egg production
• Symptoms
• - fever
• - headache
• - diarrhea
• - fatigue
• - nonspecific abdominal pain

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Stage 3 Chronic Phase

• prolonged infection (up to 10 years)
• symptoms
• - cirrhosis of the liver
• - kidney damage
• - bleeding of upper bowel
• - urinary bladder damage
• - enlargement of liver and spleen

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Slippery Little Suckers Arent They Julia
Roberts (Pretty Woman)

• Innate Immunity
• penetration of skin
• Specific Immunity
• adults take on host antigens

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Incidence
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Risk Factors

• 200 million infected globally
• 20 million with chronic schistosomiasis
• 600 million at risk
• -extreme poverty
• -lack of public health facilities
• -unsanitary conditions
• -unawareness among the people

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Prevention

• avoid swimming in fresh water in countries where
  schistosomiasis is prevalent.
• drink clean water
• scrape body down after accidental exposure
• water-resistant creams
• Snail Control

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Diagnosis and Treatment

• Diagnosis
• blood tests
• examination of stool and urine samples to detect
  eggs
• Treatment
• Drugs
• Praziquantel - effective in the treatment of all
  forms of schistosomiasis, with virtually no side
  effects
• Oxamniquine - used exclusively to treat
  intestinal schistosomiasis in Africa and South
  America
• Metrifonate - effective for the treatment of
  urinary schistosomiasis
• Vaccination
• Research efforts are directed at finding a
  vaccine, but no success

obtained from W.H.O.
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Interested in More???

• http//www.wellcome.ac.uk/en/labnotes5/animation_p
  opups/schisto.html
• http//www.cdc.gov/ncidod/dpd/parasites/schistosom
  iasis/default.htm
• http//en.wikipedia.org/wiki/Schistosomiasis
• http//www-micro.msb.le.ac.uk/224/Schisto.html
• http//www.path.cam.ac.uk/schisto/

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Questions??????