WNV Outbreaks & Climate Factors (Modified by Environmental Risk Analysis Program)

[See previous messages on related thread, Arizona, US Epicenter
2004--Why?, posted August 26, 27]

[1]
  2004 in Illinois - 5th Coolest summer since 1895 / Impact on WNV
transmission

FYI: Today, the Chicago Tribune weather section stated that this Aug
had the fewest 80 F days in 77 years (10 in 2004, 21 is normal). It is
the 5th coolest summer since 1895. This contributes to suppression of
WNV activity this year, but we can't count on record low temps in
August every summer!

High summer temperatures accelerate WNV activity in the bird and Culex
mosquito population and produces increased risk of disease to humans,
see summary that follows below -- L Haramis Ph D, Vector Control
Program

=======================================
How High Temperatures Increase the Risk of WNV

(Heat is like a throttle on a train engine... Add high temperatures,
the mosquito-virus-bird system accelerates*.)

Speed of development of mosquito larvae

Increased flight activity of Culex mosquitoes

Rate of multiplication of virus in the mosquito increases, which is
required for the mosquito to become infective

Water sources dry down and become more productive for Culex mosquitoes

Birds tend to congregate around the fewer water sources (faster virus
amplification)

People spend more time outdoors

----------------

[2]
Date: August 27, 2004 5:21:47 PM EDT

RE: "we don't see any mosquitoes."

In 2002, IL lead the nation in WNV cases. From trap counts for ALL
species of mosquitoes, the "mosquito" population was perceived by the
public as "low." (Low FLOODWATER mosquito populations; the floodwater
group is much less important than Culex in WNV transmission in IL.)

However, the INFECTION RATE in Culex (pipiens) approached 1 in 50 at
some locations in the Chicago area. (SLE in Culex is rarely more than 1
in 200- 300) Consequently, the risk of WNV transmission was INCREASING
while many citizens were saying "we don't see any mosquitoes." What we
would like the public to learn is to listen to their public health
officials and not "count mosquitoes" to estimate WNV risk.

Lots of (floodwater) mosquitoes does not necessarily mean lots of WNV
risk. This is why WNV environmental surveillance and public info are
both very important for WNV prevention.

Also, street catch basins were a major source of Culex in urban areas.
(Not too many species of frogs live in catch basins.)

The opinions above are mine and are not necessarily those of my
employer.

L Haramis Ph D, Entomologist, Vector Control Program, IL Dept of Public
Health

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Received on Wed Sep 1 15:06:30 2004