Schistosomiasis

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Author:
Anonymous
ID:
190977
Filename:
Schistosomiasis
Updated:
2012-12-31 11:05:25
Tags:
bod pathology schistosomiasis parasites
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Description:
Schistosomiasis
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  1. 3 types of schistosomes
    • Mansoni
    • Japonicum (both gut)
    • Haemotobium (bladder)
    • Martha Jasmine Helminth!
  2. Describe schistosome life cycle (inc 4 fancy words!)
    • most schistosomes crave sausages
    • Eggs in water, hatch to form Miricidium
    • Infect snails, reproduce as Sporocysts
    • In water as Cercaria
    • Penetrate skin of host (attracted by skin secretions like arginine)
    • Develop in host as schistosomulum
    • Adult schistosomes (male and female) in portal veins
    • Eggs layed into bladder (haemotobium) or intestine (mansoni, japonicum)
  3. life span of adult schistosomes, miracidium and cercaria
    • schistosomes: 20-30 years
    • miracidium: 5-6 hours
    • cercaria: 2-3 days
  4. general pathogenesis of schistosomiasis
    • skin penetration: dermatitis - 'swimmers itch'
    • acute: inflammatory response to egg deposition: 4-8 weeks after infection: fever, headaches - sudden high level of antigen exposure
    • chronic: granulomas formed around eggs in wall of intestine/portal vessels / wall of bladder/uterus/genital organs
    • eggs secrete antigens and cause T cell mediated recruitment of macrophages, eosinophils, fibrocytes � granuloma formation ad fibrosis
  5. what immune response do schistosome eggs produce?
    Th2 (IL3, 4, 5): eosinophils, macrophages, fibroblasts
  6. Describe chronic phase of S. mansoni and japonicum
    • Eggs swept back into presinusoidal capillary bed of liver
    • Fibrotic granulomas in portal vessels
    • Portal hypertension, splenomegaly, oesophageal varices, haematemesis
  7. Describe chronic phase of S. haematobium
    • Fibrotic granulomas in bladder wall, ureters, genital organs
    • Initially painless haematuria, may be intense inflammatory response
    • Later, ulceration that may lead to cancer
    • Femal genital schistosomiasis may be a risk factor in HIV transmission
  8. describe 4 main ways schistosomes evade immunity
    • Production of blocking antibodies (specific IgE and IgG4, non-specific IgE)
    • Adsorbing host proteins onto tegument
    • Protease-mediated destruction of host IgE
    • Production of immunosuppressive molecules eg ACTH
  9. describe schistosome 'blocking antibodies'
    • Specific IgE and IgG4 bind to the helminth and block the binding of Fc-epsilon-R1
    • Non-specific IgE binds to eosinophil Fc-epsilon-R1 and prevents the eosinophil binding to IgE actually bound to helminths
  10. describe function of schistosome tegument in avoiding immunity
    • The outside layer of a double lipid bilayer
    • Adsorbs host molecules so is seen as 'self': MHC, blood group, host antibodies via Fc, host lipids
    • Rapidly replaced if damaged by host immune response
    • Few schistosome antigens
  11. 5 targets for schistosome control
    • Schistosomula: vaccines
    • Adult worms: chemotherapy
    • Eggs in water: sanitation, education
    • Worms in snails: vector control - environmental, chemical, biological
    • Cercaria in water: sanitation, education
  12. how does schistosome immunity change with age?
    • More likely to be reinfected if infected when young: change in immunity at puberty
    • Infection more intense when young
  13. What drug is used against schistosomiasis? What does it do?
    • Praziquantel: kills adult worms
    • Affects Ca channels and causes paralysis
  14. 3 types of vector control against schistosomiasis
    • Environment: improve drainage, remove aquatic plants
    • Biological: competitive schistosome-resistant snails
    • Molluscisides: expensive, environmentally damaging
  15. what is concomitant immunity? Describe it in relation to schistosomiasis
    • incoming parasites fail to establish an infection in the presence of an already present infection
    • due to parasite crowding, host genetics, parasite genetics, host sex differences, age of host
  16. which gender is more susceptible to parasite infections? Why?
    Men: testosterone is immunosuppressive
  17. What is basic reproductive ratio in relation to micro- and macro-parasites
    • Micro: the average number of secondary infections triggered by a primary infection
    • Macro: the average number of female offspring produced by a parasite that survive to reproduce

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