Infections at a Snails Pace

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Infections at a Snails Pace
Bulinus
Cercaria
2
Schistosomiasis
200,000,000
Cercaria
Adult worms in copula
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Schistosoma spp. - Life cycles
Adults
Eggs
Schistosomulum
Bulinus S.h
Oncomelania S.j
Miracidium
Biomphalaria S.m
Cercaria
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Snail Ecology

• Varies for each species substrate, water flow
  rates, etc.
• Water, temperature and food determine success
• 7o 42oC general range of survival 25o optimal
  for
• reproduction
• Some species hermaphroditic (Bulinus
  Biomphalaria)
• Some species aestivate (become dormant) esp.
  during drought
• Apple snails (ampullariids) useful as biocontrol
  agents for
• Bulinus and Biomphalaria control competition
  predation

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Schistosomes - Distribution
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Schistosomiasis Distribution (cont.)
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Schistosomiasis - Ghana
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Lake Volta
200 miles long 8,500 sq. miles area 4,000 mile
shoreline
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Schistosomiasis Ghana (cont.)
S. haematobium
S. mansoni
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Schistosomiasis Ghana (cont.)
Bulinus S. haematobium
Biophalaria S. mansoni
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Schistosomiasis - Prevalence
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Schistosomiasis Age Prevalence
Fig. 1. Age-prevalence (a,d), age-intensity
(geometric mean of positive individuals) (b,e)
and age-crude index of potential contamination
(IPC) (c,f) curves for villages in six areas
endemic for Schistosoma haemotobium (ac) (green
line, Lake Volta, Ghana 6 red line, Chweshe,
Zimbabwe 7 orange line, Guia, Senegal 8) and
S. mansoni (df) (green line, Nder, Senegal 9
red line, Lake Cohaha, Burundi 10 orange line,
St Lucia 4).
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Aswan Dam Lake Nasser
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Schistosomiasis - China
1955
1996
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Schistosomiasis China (cont.)
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Schistosomiasis China (cont.)
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Schistosomiasis China (cont.)
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Schistosomiasis Pathology Immunity
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Schistosomiasis prevention
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Schistosomiasis Continuing issues

• Chronic long-lasting infection
• Snail intermediate host can be difficult to
  eradicate
• Environmental alterations to aquatic habitat may
• facilitate spread of disease
• Zoonotic potential S. japonicum
• Occupationally driven human exposure
• Inability of immune response to deal with adult
  worms
• 7. Drug cost and distribution
• Lack of a vaccine
• 9. Education