What measures of malaria do we need to monitor elimination

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What measures of malaria do we need to monitor
elimination?

• Chris Drakeley

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The Spectrum of Malaria Infection
Infectious bite
Biological parameters for assessing transmission
intensity
Infection
Clinical malaria
Less Common events identified via health
facilities or DSS
Severe malaria
Death
(Greenwood et al. Parasitology Today 19927,277.)
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(Guerra et al Plos Med 2008)
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Entomological monitoring

• Requires long term, regular monitoring
• Sampling needs to be increasingly intense as the
  number of mosquitoes (and infected mosquitoes)
  decreases.

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Mosquito human dynamics

• Routine entomology remains key for monitoring
  changes in vector behaviour
• What species are they?
• Do mosquitoes bite earlier?
• Do they bite outside?
• Are they resistant to insecticide?

(Killeen et al BMC ID 2006)
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Measuring parasites

• The gold standard measure
• Allows detection and enumeration of parasites
• Allows speciation and identification of
  potentially infectious individuals

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Limitations of microscopy

• This method is limited by how much of a blood
  film can be read.
• Ideally we need to identify all those infected (
  infectious)
• RDT have similar sensitivity to microscopy

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Progress with molecular methods

• Two new methods the LAMP (above)
• NALFIA have 5 fold better sensitivity
• that microscopy or RDT.
• Species, density and gametocytes remain issues

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Serological alternatives

• Detecting anti malarial antibodies in the blood
  of people who have been exposed to malaria is
  another approach
• Antibodies last for a long time and represent
  cumulative exposure to malaria
• Cheap, easy and high through-put
• Modern techniques are sensitive and specific

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Identification of transmission sitesregional
level

• Data from the Thai-Cambodia boarder
• Increased sensitivity of serology to allows
• Identification of potential foci of infection for
  the control of drug resistance

Cook et al unpublished
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Identification of transmission sitesvillage
level

• Data from Kenya showing that individuals closer
  to mosquito breeding sites have more antibodies
  or malaria exposure.
• Malaria transmission remains heterogenous and
• Identification and targeting high transmission
  foci within a village will be key.

Wilson et al BMC ID 2006
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Monitoring progress of the elimination effort

• Historical precedents for serological evaluation
  of malaria eradication attempts
• -Mauritius
• -Greece
• Antibodies to detect changes in exposure to both
  P.falciparum and P.vivax.

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When how to measure?

• Monitoring will require a combination of
  approaches
• Rapid situational assessments to identify key
  areas leading to
• Detailed surveys (MIS) for risk factor analysis
• Sentinel site monitoring for vector studies and
  parasite and vector resistance

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Biological tools for the eradication toolbox

• Use of existing tools to monitor entomological,
  parasitological and serological changes.
• Technological developments to increase the
  sensitivity
• Develop appropriate sampling frames for
  representative sample collection