Mosquitoes and West Nile Virus

Personal Prevention – the Four Ds

There is no treatment for West Nile virus, so it’s important to prevent it. West Nile can cause a debilitating illness in 20% of those infected. Everyone should protect themselves against mosquito bites.

Follow the 4Ds when mosquitoes are most active (June through September).

DEET

Use insect repellent that contains at least 10% DEET. If outside during evening, nighttime, and dawn hours, consider using an insect repellent containing 10% to 30% DEET (N, N-diethyl—methyl-meta-toluamide). Products with concentrations around 10% are effective for approximately two hours.

Use DEET according to the manufacturer’s directions:

• DEET is not recommended for children under two months of age.
• Do not apply DEET directly to children or to their hands. Instead, apply it to your own hands and then put it on the child.
• Apply DEET sparingly on exposed skin; do not apply under clothing.
• Do not use DEET over cuts, wounds, or irritated skin. Wash all treated skin and clothing after returning indoors.

Find the Repellent that is Right for You

Dress

Dress in long sleeves and long pants. Children and adults should wear protective clothing such as long pants, long-sleeved shirts, and socks if outside during evening, nighttime, and dawn hours when mosquitoes are most active and likely to bite.

Dusk and Dawn

Reduce or eliminate outdoor activity between dusk and dawn.

Make sure windows are closed or screened.

Most mosquito species actively search for a blood meal in the evening from just before dark until 2 to 3 hours after dark. During the daytime, females normally rest in cooler vegetated areas where the humidity is higher, and they are protected from drying out. Females will often bite in the daytime if humans or animals invade the wooded areas where they are resting.

Drain

Make sure to drain standing water around your home.

• Remove all discarded tires from your property.
• Dispose of tin cans, plastic containers, ceramic pots, or similar water-holding containers.
• Make sure roof gutters drain properly. Clean clogged gutters in the spring and fall.
• Clean and chlorinate swimming pools, outdoor saunas, and hot tubs. If not in use, keep empty and covered.
• Drain water from pool covers.
• Change the water in bird baths at least once a week.
• Turn over plastic wading pools and wheelbarrows when not in use.
• Eliminate any standing water that collects on your property.
• Remind or help neighbors to eliminate breeding sites on their properties.

Protect Your Property from Mosquitoes

What You Can Do As a Property Owner

• Empty or clean out all water-holding containers in your yard (bird baths, tires, cans, rain barrels, wading pools). One small can of water can hold as many as 10,000 mosquito larvae.
• Keep your gutters clean.
• Keep ornamental ponds free of weeds, cattails, or other aquatic vegetation.
• Use anti-larval products (dunks or bits) available at local hardware stores and use them in ponds or standing water.

Adult mosquitoes are most active at dawn and for about an hour after dusk. Plan outdoor activities during warmer daylight hours or later in the evening to avoid adult-biting mosquitoes.

• Keep your lawn mowed as short as possible.
• Cut back dense vegetation surrounding your yard; this is where mosquitoes hide during the day.
• Keep ornamental shrubs and bushes pruned to allow more light and air to flow through them.

Farmers and Agricultural Landowners

• Keep irrigation ditches free-flowing and clear of vegetation and debris.
  Repair ditches to reduce seepage.
• Minimize standing water to less than four (4) days in fields.
• Fill tire ruts and hoofprints to avoid puddles.
• Keep horse and cattle troughs clean by changing the water weekly.
• Vaccinate horses for Western Equine Encephalitis.

Report a Concern about Mosquitoes in Boulder County

Residents dealing with mosquito issues in various cities can report problems to these contacts.

Within City Limits

• City of Boulder: Ecological Mosquito Management
  • 303-441-1901
• Town of Lyons
  • 303-823-6622
• All other Municipalities: Vector Disease Control International
  • 303-466-1892

• Spray Schedule for VCDI
• Request Not to Apply Pesticides (VCDI)

Outside City Limits

• Unincorporated Boulder County: Vector Disease Control International
  • 303-466-1892

Spraying & Mosquito Concerns

• Boulder County Public Health: 303-441-1564
• COHelp Line: 1-877-462-2911
• Boulder County Public Health Hotline: 303-441-1460

Monitoring Mosquitoes in Boulder County

Boulder County Public Health (BCPH) monitors mosquito populations, especially the Culex species, to determine the risk to people.

BCPH has traps throughout Boulder County so that we can count

• Total number of mosquitoes
• Percentage of Culex mosquitoes
• Percentage of mosquitoes with West Nile virus
• Number of human cases
• Number of human deaths

The Culex mosquito is a carrier of West Nile virus in Colorado. It is common in Boulder County and takes about two weeks to grow in warm weather. Getting rid of standing water can help stop them from multiplying.

Learn more about Culex mosquitoes (CDC)

Current Mosquito Activity in Boulder County

BCPH looks at mosquitoes captured in traps throughout Boulder County and tracks the data for trends.

Current Total Mosquito Activity in Boulder County

Total Mosquitoes: Weekly Comparison by Year

Total Culex: Weekly Comparison by Year

Vector Index

The vector index, which measures the risk of the virus spreading, depends on the number of Culex pipien and Culex tarsalis mosquitoes trapped and tested. If the vector index reaches 0.75 or more, there might be a need to take action to reduce the number of mosquitoes in Boulder County. We do this by using:

• Larvicide: A substance used to kill mosquito larvae before they become flying mosquitoes. This helps lower the number of mosquitoes spreading viruses like West Nile.
• Adultize: Adultizing is a method of controlling the population of mosquitoes. This method reduces their numbers, especially when the risk of spreading viruses, measured by the vector index, is high in Boulder County.

The vector index helps to figure out the risk of the virus spreading based on

• The total number of the species of mosquitoes that can carry West Nile (Culex pipien and Culex tarsalis).
• The number of infected mosquitoes in an area.
• The vector index calculates the average number of infected mosquitoes collected per trap in an area.
• If it reaches 0.75 or more, mosquito spraying might be needed to lower the risk.

Map of Zones Where Mosquitoes Are Trapped

West Nile Data

• Colorado Department of Public Health & Environment
• Centers for Disease Control & Prevention

Effective Mosquito Management

A comprehensive mosquito management strategy is employed to address the dual challenge of nuisance and potential health risks posed by mosquitoes as carriers of the West Nile virus. The approach is anchored in Integrated Pest Management (IPM), a method designed to reduce mosquito populations effectively while prioritizing environmental friendliness and cost-effectiveness.

This approach focuses on preventing breeding by

• Eliminating stagnant water
• Using natural solutions like Bti bacteria
• Introducing native fathead minnows
• In cases of high mosquito numbers, permethrin, a synthetic chemical derived from the natural insecticide found in chrysanthemum flowers, is used cautiously to minimize environmental impact.

Boulder County Mosquito Control District (BCMCD)

The Boulder County Mosquito Control District (BCMCD) works to keep residents safe from mosquito-related health issues. Meetings, either virtual or by phone, help everyone stay connected and informed. Annual reports give a peek into ongoing mosquito control efforts.

West Nile virus (WNV) poses a significant health concern in Colorado. Approximately 20% of those infected may experience severe symptoms, ranging from fever and fatigue to more serious conditions like meningitis or paralysis.

• West Nile Symptoms, Diagnosis & Treatment
• Information for Healthcare Providers

These guidelines are provided to assist health care providers and educators with the recognition and diagnosis of illness due to West Nile virus (WNV).

• CDPHE West Nile Virus Information
  Get general clinical information on WNV as well as professional resources for health care providers from the Colorado Department of Public Health and Environment.
• CDC West Nile Virus Guidance for Clinicians
  Access information from the Centers for Disease Control and Prevention on WNV including:
  • Background
  • Epidemiology
  • Clinical Description
  • Treatment
  • Reporting
• West Nile Virus Fact Sheet
• Guidelines for Surveillance, Prevention and Control

Please feel free to download, reproduce, and distribute these materials.

One Bite Campaign

The One Bite campaign was developed in 2003 when Boulder County had an extreme number of people who contracted West Nile virus. A significant number of residents died or had long-term or permanent complications.

One Bite Poster

• West Nile Virus Alert Poster
• Alerta sobre el Virus del Nilo Occidental

Flyers for Distributing at Events

• Cody Kinney West Nile Virus Alert
• Nancy Foster West Nile Virus Alert
• Shelley Bailey West Nile Virus Alert
• Michael Paquin West Nile Virus Alert

Flyer for Mailings

• West Nile Virus flyer