Schistomiasis

Schistomiasis

1. background

   • blood bourne fluke
   • separate sexes
   • endemic in 70 tropical and sub tropical countries
     • effects - kidney failure, hypertension
   • 3 major human schistome species
     • S. japonicum
       • intestinal
       • S E Asia
     • S. mansoni
       • Africa, S. America
       • intestinal
     • S. haematobium
       • Africa
       • urogenital
   • both ancient and modern disease
   • lots of types
     • different animal hosts

2. life cycle

   • 2 stage process
     • infective and diagnostic
   • acquire by going into the water
   • schistosome released in faeces and urine
     • eggs hatch in water
       • miracidia released
         • penetrate snail tissue
           • sporocysts in snail
             • cercariae released by snail into water
               • penetrate skin of host
                 • migrate to portal blood
                   • mature into adults
                     • pair worms migrate to bowel/bladder and lay eggs

3. identification

   • urine/stool samples
     • count eggs to measure infection intensity

4. changing environments

   • dams
     • new freshwater environment where snails thrive
   • livestock practices
   • hybrids
     • closely related species mate
     • very prevalent in W Africa since 1940s

5. schistosomes maximise fitness over changing environment

   • ASIA
     • older selective pressure
     • S. japonicum
       • endemic in 7 provinces and re emrging
       • 30 million at risk
       • reasons for persistence
         • only sch which zoonotic transmission is important
         • over 40 species serve as reservoir hosts
       • faecal samples for s japonium and s mansoni
         • look at parasite genomes
         • results
           • S japonicum low in humans
           • high prevalence/ intensity in bovines in marshland
           • high prevalence/intensity in rodents in hilly
             • super spreaders
           • higher infection in hilly than marshland
           • cercarial behaviour
             • inter specific variation in shedding in relation to host
             • maximise transmission
             • spread due to cattle and rodents
               • host switching
   • AFRICA
     • newer selective pressure
     • drug pressure
       • SCI
       • sustainable drug admin programmes
         • PZQ
           • designed to reduce morbidity
             • WHO now wants to eradicate it
           • 2003-2013 >90% SSA
         • target those at high risk
           • pregnant, children
     • drug resistance
       • no evidence in china
       • antihelmintics resistance
     • mass drug admin in niger
       • bring down prevalence and intensity of s. haematobium
       • few villages still have infection
         • no drug resistance
       • rapid reinfection
         • ZOONOTIC HYBRID