The Epidemiology of Malaria Outbreaks

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The Epidemiology of Malaria Outbreaks

  1. 1. <ul><ul><li>Key determinants of malaria endemicity/epidemics </li></ul></ul><ul><ul><li>The Uganda malaria epidemic 1997/98 </li></ul></ul>The Epidemiology of Malaria Outbreaks: What do we really know ?
  2. 2. Determinants of Malaria Parasite Vector Host Environment
  3. 3. Determinants of Malaria Environment
  4. 4. Immunity Transmission <ul><ul><li>Competent vector species </li></ul></ul><ul><ul><li>Suitable breeding sites </li></ul></ul><ul><ul><li>Sufficient temperature </li></ul></ul><ul><ul><li>Humidity, soil moisture </li></ul></ul><ul><ul><li>Reservoir of parasites </li></ul></ul>Temporary (rain) A. gambiae s.l . Permanent (rain, drought) A. funestus . <ul><ul><li>Repeated exposure </li></ul></ul><ul><ul><li>Mature immune system </li></ul></ul>Anti-disease No syptoms Anti-parasite Low Parasites <ul><ul><li>Age </li></ul></ul><ul><ul><li>Pregnancy </li></ul></ul><ul><ul><li>Disease/Nutrition </li></ul></ul>Determinants of Malaria
  5. 5. Immunity Transmission Hypoendemic Mesoendemic Hyperendemic Holoendemic No Malaria <ul><ul><li>In a stable malaria situation an equilibrium exists </li></ul></ul><ul><ul><li>This may, however, include strong seasonality </li></ul></ul>Determinants of Malaria
  6. 6. <ul><ul><li>Gradual, long-term change >> new equilibrium </li></ul></ul><ul><ul><li>Sudden, temporary change >> outbreak </li></ul></ul><ul><ul><li>Any change in the determinants of malaria will lead to a disturbance of the equilibrium </li></ul></ul><ul><ul><li>This may occur at any level of endemicity </li></ul></ul>Epidemic Outbreak Children, pregnant women Total population <ul><ul><li>When does seasonal variation become an epidemic ? </li></ul></ul>Determinants of Malaria
  7. 7. <ul><ul><li>Since epidemic in the past have rarely been anticipated, usually only routine data from health services exist </li></ul></ul><ul><ul><li>We have no clear understanding how the various clinical parameters (out-patient attendance, severe malaria cases, slide positivity rate) relate to each other and to the dynamic of transmission </li></ul></ul><ul><ul><li>This knowledge is important for early detection as well as control </li></ul></ul>Documentation of Epidemics
  8. 8. The Uganda Malaria Epidemic 1997/98 <ul><ul><li>Recognition only through press/politicians </li></ul></ul><ul><ul><li>Retrospective analysis </li></ul></ul><ul><ul><li>El Niño associated </li></ul></ul>
  9. 9. The Uganda Malaria Epidemic 1997/98
  10. 10. The Uganda Malaria Epidemic 1997/98
  11. 11. The Uganda Malaria Epidemic 1997/98
  12. 12. The Uganda Malaria Epidemic 1997/98 Monthly rainfall around epidemic years, Kabale District
  13. 13. The Uganda Malaria Epidemic 1997/98
  14. 14. The Uganda Malaria Epidemic 1997/98 Clinical malaria cases in health facilities Kabale District Endemo-epidemic channel and 1998 data
  15. 15. The Uganda Malaria Epidemic 1997/98 Relationship between altitude and malaria endemicity Village parasite rate Zalueta 1959 Kigezi Kilian 1994-1997 Kabarole Probability of being parasitemic, Kabarole, 8,000 children 0-10 years
  16. 16. The Uganda Malaria Epidemic 1997/98 Intensity of epidemic at decreasing levels of altitude
  17. 17. The Uganda Malaria Epidemic 1997/98
  18. 18. The Uganda Malaria Epidemic 1997/98
  19. 19. <ul><ul><li>Malaria outbreaks/epidemics are part of the rather complex epidemiology of malaria </li></ul></ul><ul><ul><li>There is no sharp distinction between endemic and epidemic prone situations </li></ul></ul><ul><ul><li>Which factors trigger epidemics in which way is not yet fully understood </li></ul></ul>The Epidemiology of Malaria Outbreaks: J. Najera, P. Langi, A. Talisuna, J. Cox

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