HomeMy WebLinkAboutMemo - Mail Packet - 10/4/2022 - Memorandum From Matt Parker Re: West Nile Virus (Wnv) - Final 2022 Season Memo 1745 Hoffman Mill Road
PO Box 580, Fort Collins, CO 80522-0580
MEMORANDUM
Date: September 22, 2022
To: Mayor and City Councilmembers
From: Matt Parker, Sr. Supervisor, Natural Areas
Amy Resseguie, Lead Specialist, Communications & Public Involvement
Through: Kelly DiMartino, City Manager
Tyler Marr, Interim Deputy City Manager
Seve Ghose, Director, Community Services
Mike Calhoon, Director, Parks
Katie Donahue, Director, Natural Areas
Subject: West Nile virus (WNV) Final 2022 WNV Season Memo
Summary:
This memo documents the conclusion of the mosquito trapping and testing season for the City
of Fort Collins. The 2022 season brought about higher than average temperatures, and regular
monsoonal precipitation and resulted in significantly higher mosquito abundance than average.
This led to spray applications occurring both earlier and more frequently than most years.
Current Vector Index:
Week No: 37 Vector Index
Threshold:
Previous Week Vector
Index:
Current Vector
Index:
FC Zone NW NA 0.06 0.00
FC Zone NE NA 0.09 0.37
FC Zone SE NA 0.11 0.06
FC Zone SW NA 0.00 0.00
FC Citywide NA 0.08 0.11
Floating Zone 0.75 0.42 0.41
Current Conditions: Five trap locations tested positive across the city, four of which are in the
NE quadrant of the city. Mosquito populations are declining, although abundance in the NE
quadrant remains very high for this time of year. The low weather system moving in this week is
likely to have suppressive effects on the population.
Season Summary: The 2022 mosquito season jumped off to an early start with elevated WNV
vector index levels earlier in the season than is typical. The vector index is the product of
mosquito abundance and infection rate within the trapped samples. Drier weeks in the early
season suppressed mosquito abundance, however once the monsoonal pattern developed,
mosquito populations drastically increased, exceeding the historic average across the city, as
City of Fort Collins
shown in the chart below. These higher than typical abundance numbers kept the WNV vector
index high for the remainder of the season. Infection rates largely tracked with historic values
with a few late season exceptions showing higher than normal infection rates during week 36 in
the NW and SE quadrants. Higher abundance values coupled with average infection rate values
lead to higher WNV risk throughout the summer as measured by the vector index. Larimer
County issued spray recommendations based on data from weeks 30, 34, 35, and 36.
The adult mosquito spray element of the WNV Management Program is designed to target
areas of high WNV risk as quickly and as geographically targeted as possible. This year four
distinct applications were made totaling 39 square miles. While it is impossible to understand
how the virus would have behaved without intervention, the worst-case scenario are
applications involving the entire city, or roughly 53 square miles, as occurred in 2007 and 2013.
Outreach and Public Awareness:
West Nile awareness advertising and other public outreach has concluded for the season.
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