Environmental Surveillance

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Environmental Surveillance

• Nick Komar, ScD
• CDC DVBID
• Fort Collins, CO

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• Surveillance Guidelines
• Pdf available at www.cdc.gov (updated in 2003)
• Each surveillance modality described with its
• PURPOSE
• ADVANTAGES
• DISADVANTAGES
• Stresses that ecologic surveillance without a
  purpose wastes resources

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Environmental Surveillance Modalities

• Vector density and infection rate
• Sentinel captive birds
• Sentinel free-ranging birds
• Avian mortality surveillance
• Non-human morbidity mortality surveillance

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Environmental Surveillance Modalities

• Vector density and infection rate
• Sentinel captive birds
• Sentinel free-ranging birds
• Avian mortality surveillance
• Non-human morbidity mortality surveillance

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Vector Surveillance

• Purpose
• Monitor populations of mosquitoes
• Estimate risk of infectious mosquito bites
• Monitor risk in long-term surveillance sites
• In traditional transmission foci
• In population centers
• Determine local risk in response to other
  indicators of virus activity (such as a human
  case or a WNV dead bird)

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Vector Surveillance

• Number of USA counties reporting vector data
  toArboNET is stable at about28 (poster 27)
• Advantages
• Provides a relative measure of risk
• PPV of an infected mosquito is about 50 for
  human cases (poster 27)
• Disadvantages
• Mosquito ID is labor intensive
• Effort is Active, not Passive
• Data geographically limited by trapping effort

Pos
Neg
NT
ArboNET 2008
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Advances in Vector Surveillance

• Culex vectors well characterized throughout the
  US and Canada, permitting targeted collection
  practices
• Gravid traps for Cx. pipiens complex
• CO2-baited light traps for Cx. salinarius and Cx.
  tarsalis
• Molecular techniques now widely available for
• Culex species ID
• Bloodmeal source ID
• Vectorial risk indices have been developed
• More user-friendly than vectorial capacity
  equation
• Improved mosquito traps

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Vector Indices

• Nasci Vector Index
• Infection rate (IR) x Trap index (TI)
• units number of infected Culex pipiens per trap
  night
• Kilpatrick modified vector index
• IR x TI x competence x human feeding index
• Unitsnumber of infectious Cx. pipiens that will
  bite humans per trap night
• Requires more resources but theoretically
  provides a better estimate of local risk

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Trap Improvements

• Updraft gravid trap
• Propane-powered mosquito magnet trap
• CDC Resting Trap (poster 77)

Panella et al. unpublished data
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Avian Mortality Surveillance

• PURPOSE
• Early detection of transmission foci
• Confirmation of ongoing local transmission
• In some cases, quantify transmission risk (e.g.
  see Poster 35)
• Not the original purpose, but numerous studies
  across the country have found ways to use dead
  bird reports and avian carcass testing to
  quantify transmission and predict risk more
  details will be presented and discussed in
  breakout session Friday evening.
• Indirect objectives
• Cooperate with other surveillance systems (e.g.
  H5N1 AI)
• Detect novel pathogens

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Trends in Data Reporting
ArboNET 2003
ArboNET 2008
Pos
Pos
Neg
Neg
NT
NT
Dramatic reduction in USA counties reporting
avian mortality surveillance data in last 6 years
(see poster 27).
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Advantages

• Temporally sensitive when effort is intensive
  early in the season (multiple species targetted)
• Spatially sensitive
• No longer requires specialized laboratory
  facilities or skills
• Highly cost-efficient due to very high detection
  rates

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Disadvantages

• Triage systems need constant attention
• Utility of crows has diminished as predicted
• Success depends on strong support and
  participation from the public and strong
  interagency cooperation
• Poor fit with public health culture

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Selected advances

• WNV-pos carcasses (mainly corvids) predicted
  human cases in Colorado (Patnaik et al. EID
  2007)
• DYCAST model effective for predicting human risk
  in California (poster 35)
• Sample collection facilitated by using immature
  feathers (Docherty et al. EID 2004) and mature
  feathers (poster 13)

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Mature breast feathers

• Reduction in sensitivity (52 in WNV-pos. corvid
  carcasses) offset by ease of sample collection
• Cold chain obsolete
• No infectious fluids

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The Big Picture

• WNV HAS BECOME ENDEMIC
• Diminishing resources
• Learning to live with WNV does not mean
  complacency
• Creative and cost efficient strategies needed to
  mitigate an omnipresent risk
• Environmental surveillance is crucial to this
  challenge