HomeMy WebLinkAboutMemo - Mail Packet - 06/17/2025 - Memorandum from Ryan Vincent re West Nile Virus – Program Orientation and Communications OverviewNatural Areas Department
1745 Hoffman Mill Road
PO Box 580, Fort Collins, CO 80522
970-416-2493
rvincent@fcgov.com
CC: Mike Calhoon, Director, Parks; Katie Donahue, Director, Natural Areas; Matt Parker, Ecological Stewardship
Manager, Natural Areas 1
MEMORANDUM
Date: June 10, 2025
To: Mayor and City Councilmembers
Through: Kelly DiMartino, City Manager
Tyler Marr, Deputy City Manager
Dean Klingner, Community Services Director
From: Ryan Vincent, Senior Supervisor, Natural Areas
Subject: West Nile Virus – Program Orientation and Communications Overview
BOTTOM LINE
Staff is providing the following information to help City Council respond to community questions
or concerns about West Nile Virus as they arise:
1. An overview of West Nile Virus
2. Background on the City’s West Nile Virus Program
3. A summary of communications Council can expect throughout the summer
OVERVIEW OF WEST NILE VIRUS (WNV)
WNV poses an annual, seasonal threat to the health of community members.
Two of the twelve common local mosquito species, Culex pipiens and Culex tarsalis, spread
WNV. Birds serve as perennial reservoir hosts. As the virus builds up in birds over the summer,
the risk of mosquito transmission to humans rises. Peak risk occurs from mid-July to mid-
September, particularly in the northeast and southeast areas of Fort Collins.
While older adults and outdoor workers face higher risk, WNV can cause severe or fatal illness
in anyone.
WNV is most often asymptomatic, but about 1 in 5 infected people may develop mild symptoms
like fever, headache, body aches, and fatigue. In rare cases - about 1 in 150 - it can cause
severe illness affecting the nervous system, such as encephalitis or meningitis, which may lead
to long-term neurological damage or even death.
Larimer County residents report an average of 15 WNV cases each year. In 2024 there were 5,
which coincided with below-average mosquito abundance and below-normal precipitation in
spring and summer.
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BACKGROUND ON THE CITY’S WNV PROGRAM
For the past 22 years, Fort Collins has partnered with the Larimer County Department of Health
and Environment (LCDHE), the CDC, and CSU to build a program that aims to reduce the risk
of WNV within the community. The WNV Program primarily focuses on public education and
mosquito larvae control through breeding site reduction and targeted larval control. As an
emergency response, the program facilitates communication and awareness of data-supported
adult mosquito treatments.
The City’s public outreach focuses on two key messages: 1) education about WNV and ways for
individuals to reduce their risk, and 2) encouraging residents to sign up to receive Larimer
Emergency Telephone Authority alerts about spray events.
To manage mosquito larvae, Vector Disease Control International (the City’s contractor) seeks
out and monitors breeding sites, then applies selective larvicide to sites containing Culex larvae.
LCDHE may recommend targeted applications to reduce adult mosquito populations based on
mosquito surveillance data. LCDHE uses the City’s 53 established mosquito traps to collect
weekly WNV data and calculate a vector index (VI). The VI describes the risk of disease
infection by calculating the mosquito abundance and the virus rate within the mosquito
population. If the VI exceeds 0.75 in an area containing at least five adjacent traps, LCDHE may
recommend spraying the area.
COMMUNICATIONS COUNCIL CAN EXPECT THROUGHOUT THE SUMMER
Staff will send weekly memos between June 15 and September 21 to update Council on:
✓ LCDHE recommendations for data supported adult mosquito spraying
✓ WNV activity across the city
✓ Relevant information, including weather patterns, mosquito activity, and program
updates
If LCDHE recommends spraying for adult mosquitoes, staff will include the memo in the
Tuesday read-before packet, ensuring Council receives all necessary details before spraying. If
LCDHE does not recommend spraying, the memo will appear in the Thursday Council packet.
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