HomeMy WebLinkAboutMemo - Mail Packet - 08/13/2024 - Memorandum from Ryan Vincent re: West Nile Virus (WNV) – Weekly UpdateNatural Areas Department
1745 Hoffman Mill Road
PO Box 580, Fort Collins, CO 80522
970-416-2493
rvincent@fcgov.com
CC: Dean Klingner, Community Services Director; Mike Calhoon, Parks Director; Katie Donahue, Natural Areas
Director; Matt Parker, Natural Areas Ecological Stewardship Manager
MEMORANDUM
Date: August 6, 2024
To: Mayor and City Councilmembers
Through: Kelly DiMartino, City Manager
Tyler Marr, Deputy City Manager
From: Ryan Vincent, Natural Areas Sr. Supervisor
Subject: West Nile Virus (WNV) – Weekly Update
KEY POINTS
• The Larimer County Department of Health and Environment (LCDHE) reported the
first human case of WNV in the county this week and continues to monitor new
possible cases. Historically, most WNV cases are reported in August. There have been
seven human cases of WNV reported in Colorado as of July 29. State health officials
have not updated this information to reflect new cases confirmed since then.
• LCDHE is not recommending spraying for adult mosquitos at this time, however,
WNV activity is increasing in localized areas.
• An area in the SE quadrant reached a Vector index (VI) of 0.73 this week, just shy
of the 0.75 threshold for spraying. The trapping network detected three WVN-positive
mosquito traps in the SE quadrant and one in the NE. Data over the past two weeks
suggests higher WNV activity in sub-quadrant areas within the SE quadrant. When
identifying potential treatment areas, staff calculate VI values based on floating zones
that consist of 5 or more traps within or across quadrant boundaries. If the VI exceeds
0.75, LCDHE may recommend adult mosquito treatment.
• Data shows increased WNV activity even in dry conditions. General understanding
of mosquito ecology suggests that WNV activity may increase during dry periods due to
the concentration of viral hosts (birds) around limited water sources. With birds
concentrated, mosquitoes more efficiently transmit WNV to a greater number of birds
thereby amplifying the viral cycle.
• Additional messaging targeted to neighborhoods with higher WNV activity is
planned for this week, encouraging residents to remain diligent about personal
protection measures.
Docusign Envelope ID: ABA1A801-3A81-46CF-92C4-BEA2DE608EFD
CURRENT VECTOR INDEX INFORMATION
VI Threshold: Previous Week VI: Current VI:
FC – Zone NW NA 0.00 0.00
FC – Zone NE NA 0.00 0.10
FC – Zone SE NA 0.10 0.21
FC – Zone SW NA 0.00 0.00
FC – Citywide NA 0.04 0.10
Floating Zone 0.75 0.34 0.73
A floating zone with a vector index of 0.73 was located between Timberline Road and I-25, and
between Harmony and Carpenter Roads in the southeast quadrant.
MORE ABOUT THE VECTOR INDEX
WNV activity, shown as a VI, is a calculation of the abundance of the two species capable of
transmitting WNV and the rate of WNV infection within those mosquitoes. This data is collected
using the City’s network of 53 traps.
Staff calculates the VI over various spatial levels (citywide, quadrant, and 5-trap floating zone)
to identify opportunities to break the virus amplification cycle as early as possible. City and
County staff identify the smallest effective treatment zone to minimize impacts to the community
and the environment.
Currently, there is a below average abundance of mosquitoes coupled with infection rates that
are slightly above historic levels. Since the VI calculation takes both these factors into account,
higher VIs are possible in dry years with below average mosquito abundance but elevated
infection rates.
CITY OF FORT COLLINS’ ROLE IN ADULT MOSQUITO TREATMENTS (SPRAYING)
If the LCDHE makes a recommendation to spray, City staff may facilitate a spray operation. The
community will be notified through email and text notifications as well as broad communication
through the City’s various external communication channels. Community members can sign up
for alerts through nocoalert.org.
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ADDITIONAL INFORMATION
• Citywide public outreach is ongoing and includes social media posts, utility bill inserts,
and other advertising. Outreach information is centered on the “4Ds” messaging, which
encourages people to Drain standing water, Dress in long pants and sleeves to deter
biting, Defend with EPA-approved repellant, and avoid the high mosquito activity time
between Dusk & Dawn. Messaging also encourages community members to opt in to
receive notification about any future spray events.
• Preventative WNV management actions are in full swing with larval treatments, trapping,
and testing.
• Vector Disease Control International is not planning to spray any Fort Collins HOAs this
week for nuisance mosquitos.
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