HomeMy WebLinkAboutMemo - Mail Packet - 10/29/2024 - Memorandum from Ryan Vincent re West Nile Virus (WNV) – Season SummaryNatural 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: October 21, 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 – Season Summary
BOTTOM LINE
This memo provides a summary of the 2024 West Nile Virus (WNV) season, including details on
weather conditions, mosquito abundance, mosquito surveillance and testing, larval control
efforts, WNV case data, and outreach activities.
BACKGROUND
2024 Season Summary: This summer
was hotter and drier than average. Local
weather data shows that Fort Collins
received 54% of average rainfall between
June 1 and Sept. 30. During this same
time, temperatures were three degrees
above normal. Mosquito ecology research
suggests that these hot and dry conditions
reduce the number of breeding pools and
therefore limit mosquito populations.
Trapping data confirms that mosquito
abundance fell below historical averages
for the entire season.
Despite low mosquito abundance WNV was still present in the community. Although vector
indexes stayed below the 0.75 spraying threshold, floating zones reached 0.73 during the
weeks of Aug. 4 and Sept. 28. This situation can occur during dry periods when birds gather
around limited water sources, allowing mosquitos to more efficiently transmit WNV, amplifying
the viral cycle.
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Surveillance and Testing: Trapping and testing local mosquitos for WNV is a crucial part of the
WNV program. The Larimer County Department of Health and Environment (LCDHE) uses this
data throughout the season to calculate vector indexes and determine if spraying is necessary.
Over 15 weeks, Vector Disease Control International (VDCI) collected mosquitos from traps at
53 locations across the city. VDCI collected 40,597 mosquitos, and nearly one-third were Culex,
which may transmit WNV.
VDCI sent 1,116 pools of Culex mosquitoes containing 50 individuals each to the Colorado
State University Department of Microbiology, Immunology, and Pathology (CSU) for virus
testing. CSU found that 44 pools tested positive for WNV.
Adult Mosquito Control: LCDHE did not recommend adult mosquito spraying this year, though
some private homeowners’ associations contracted with VDCI to spray for nuisance mosquitos.
Larval Control: VDCI conducted larval mosquito control to reduce adult mosquito numbers.
Technicians made 5,554 site visits and treated 2,196 acres with larvicides, primarily using the
naturally occurring soil bacteria Bacillus thuringiensis israelensis.
WNV Human Cases: As of the latest update on Oct. 16, 2024, WNV data from state and county
health departments show that all reported categories are below the five-year average.
Year Statewide
Cases
Statewide
Deaths
Statewide
Neurologic
Symptoms
Statewide
Hospitalizations
Larimer County
Cases
2024 71 4 38 24 5
2023 634 51 311 386 52
2022 207 20 120 143 15
2021 173 12 93 113 27
2020 35 1 17 19 3
2019 122 8 53 51 7
5-year
Average
234 18 119 142 21
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Community Outreach: Because there were no recommended spray events this season, all
public outreach and communications focused on education, awareness and the 4Ds prevention
measures:
✓ Drain standing water
✓ Dress in long pants and sleeves
✓ Defend with an EPA-approved repellant
✓ Avoid outdoor activity between Dusk and Dawn
Communication efforts used a variety of channels, including website content, regular social
media posts, utility bill inserts, City newsletters, streetlight banners, bus shelter ads, and print
and digital ads in the Coloradoan. Additionally, program staff engaged with community members
and distributed repellent wipes at two CSU Lagoon Series concerts.
Staff also updated and streamlined the spray notification process, removing the phone call
option and shifting to text and email alerts only. In addition to promoting the opt-in spray
notifications in all WNV communications, staff mailed a postcard citywide in early July to inform
community members of how to sign up for alerts and/or update their notification preferences.
This direct mail effort resulted in a 24.2% increase in total subscribers, including an 87.9%
increase in text message subscribers.
Postcard mailed to residents in July
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Funding and Expenditures: BFO supports the WNV program within the Safe Community
Outcome Area with an offer amounting to $386,756, which covers the program's direct costs
financed through the General Fund. The CMO Emergency Fund provides funding for spraying
when needed. The Natural Areas Department and the Communications & Public Involvement
Office handle staffing for program administration and public outreach efforts.
2024 WNV Program Expenditures
Trapping and larvicide applications by
VDCI
$319,661
WNV lab testing by CSU $48,512
Adulticide applications performed by
VDCI
$0
Community outreach items including
postcards, materials for outreach events,
digital and print ads, utility bill inserts and
other outreach related services
$18,583
Total $386,756
NEXT STEPS
The WNV Technical Advisory Committee, consisting of staff from the City and County, CSU,
and Centers for Disease Control, will review the 2024 season and propose areas for
improvement. The committee will meet in February, with additional meetings as needed. Staff
will provide a memo summarizing the meeting's findings in June 2025.
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