West Nile Virus and Mosquito Control

1. West Nile Virus and Mosquito Control K. Bennett, R.P. Bio. Manager, Environment Services May 2003

2. 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.

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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”