Surveillance of Dengue Vector Using Ovitrap

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Surveillance of Dengue Vector Using Ovitrap
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The Vectors

• Aedes albopictus
• Native to Southeast Asia
• Peri-domestic
• Breed and bite outdoors
• Also breed in natural containers
• Biting Peak before dusk

• Aedes aegypti
• Imported from Africa
• Domesticated
• Breed and bite indoors
• Only breed in artificial containers
• Biting peak morning

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Biology of Aedes mosquitoes in relation to dengue
transmission

• Short breeding cycle 7 days - 10 days
• Domestic breeding habitats and peri-domestic,
  multiple breeding sites
• Eggs withstand desiccation (transportation via
  eggs)
• Biting habits day light hours
• Anthropophilic behaviour

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Biology of Aedes mosquitoes in relation to dengue
transmission

• Vertical infection of eggs
• Flight range
• 90 less than 100m
• female max. 500m
• Male max. 200m
• Several blood meal in one single gonotropic cycle
• Not laying all mature eggs in one single
  oviposition

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Conventional Aedes Surveys

• Container Index ( proportion of ve containers)
• House Index (proportion of ve houses)
• Bruteau Index (relationship between ve
  containers and houses)

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Interpretation of Transmission Risk

• Based on container count, not larvae
• The sampling unit is house or premise, hard
  to define in multistory apartment, blocks and
  public places
• Do not address adult productivity

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New Indices

• Pupal Index No. of pupae / 100 houses
• Potential Container Index No. of potential
  breeding sites / 100 houses
• Aedes density Index No. of Aedes larvae / house
• Ovitrap Index of Aedes positive ovitrap

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Oviposition Trap

• Surveillance tool (airport, seaport, public
  areas)
• Assessment tool (assess specific control
  operation, e.g. fogging)
• Research tool (season prevalence, collect samples
  for research purposes)
• Control tool (autocidal ovitrap)

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Objectives of Ovitrap Survey

• To study and monitor the distribution of the
  Aedes albopictus at selected areas
• To serve as a tool to monitor the effectiveness
  of mosquito prevention and control work carried
  out by the District Pest Control Staff of FEHD
  and other concerned departments
• To provide surveillance information to effect
  changes in control strategies if necessary.

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Methodology

• Ovitrap 200ml black plastic container
• 6.5 cm diameter, 10.0 cm in height
• Brownish oviposition paddle
• Fill up with water to 80 full
• 55 Ovitraps in each survey area ( 0.55km2
• Each 100m apart

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Methodology

• Set in field for one week
• Incubate in laboratory for eggs to hatch out and
  examine when the larvae reach their 3rd instar

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Methodology

• Study area areas with high human concentrations
  such as housing estates, hospitals, schools, etc
  (as recommended by WHO)
• Also includes other risky areas such as cargo
  working areas, Macau Ferry Terminals, etc.

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Methodology

• 38 locations selected in 2002 for the survey
• Each location reviewed every 4 months
• 3 cycles each year

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Interpretation of Results

• Enumeration of Ovitrap Index
• Ovitrap Index No. of Aedes ve traps /
  Total no. of traps
• Enumeration of Monthly Ovitrap Index

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Follow-up Actions

• District pest control staff informed of the
  results of the survey
• Carry out thorough survey and larval control
  actions at 100m radius around the Aedes positive
  traps

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THE END
Thank You