West Nile Virus and Mosquito Control

1
West Nile Virus and Mosquito Control

• K. Bennett, R.P. Bio.
• Manager, Environment Services
• May 2003

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Discussion

• West Nile Virus
• Target species of mosquitoes
• Target mosquito habitat
• Integrated Pest Management Principles
• Treatment methods
• Potential program for 2004

3
West Nile Virus (WNV)

• Discovered in the West Nile region of Uganda
  1937 appeared in New York City, 1999
• The BC Health Ministry is expecting West Nile to
  appear in BC this summer.
• Crows, Ravens and Jays are the local reservoir
  for the virus, but many species of birds are
  infected worldwide.
• Certain species of mosquitoes become infected by
  biting an infected bird.
• West Nile Virus is then spread to humans by the
  bite of an infected mosquito.

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WNV

• The risk of becoming seriously ill as a result of
  the West Nile Virus is very low and most people
  who become infected experience no symptoms or
  have very mild illness.
• However, in rare situations, it can cause
  encephalitis (inflammation of the brain).
• Mammals usually do not pass the virus on and are
  considered a dead-end host
• The virus is not spread by direct
  person-to-person contact, or from animal to human

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Target Species of Mosquitoes

• Not all mosquitoes bite people
• Some mosquitoes prefer birds for the blood meal
• Some mosquitoes bite both
• Not all species can transmit WNV
• The target species, therefore bite both people
  and birds and are capable of transmitting the
  disease

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Target Species of Mosquitoes

• There are 5 species in BC capable of transmitting
  WNV
• In the Lower Mainland, the target species are
  Culex pipiens (the house mosquito) and Culex
  tarsalis.
• Both bite birds and people, although Cx. pipiens
  bites mainly birds and occasionally people
• Cx. Pipiens is more common than Cx. tarsalis

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Target Species of Mosquitoes

• Cx. tarsalis and Cx. pipiens overwinter as mated
  females
• Lay eggs on the edges of water after a blood meal
  in the spring
• Both have several generations per season

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Target Mosquito Habitat

• Cx. pipiens and Cx. tarsalis prefer stagnant,
  contained water
• Cx. pipiens prefers water with high organic
  content, low oxygen, such as stale bird baths,
  pool covers, stagnant ditches, polluted ponds,
  where there are few predators
• Cx. Pipiens is the most common mosquito in
  artificial containers
• Healthy wetlands keep mosquito populations in
  check

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Integrated Pest Management

• Identify the adult species present
• Identify the target habitat
• Map and record the habitat
• Survey the habitat for the presence of larvae
• Target the larval stage for treatment
• Educate the public on personal protection and
  elimination of stagnant water around the home

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Treatment Methods

• Once habitat is identified and known to produce
  the target species, then the water can be either
  drained or treated to kill the larvae.
• Treatment is with Bacillus Thuringiensis (Bt)
• Bt targets mosquito larvae specifically with
  little impact on non-target species.
• Bt will be available to the public for use on
  private property
• Spraying for adult mosquitoes is not desirable
  and least effective

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2004

• Survey for target mosquito habitat
• map identified sites to the GIS
• monitor sites for larvae
• Treat with Bt as needed
• Use contractor or
• Mosquito control program in house