- Ensure greenbelts and all common areas have good drainage and tall grasses are cut
- Repair broken sprinkler heads
- Report standing water in nearby irrigation canals after the water has been turned off
- Add larva-killing Bti* granules or “dunks” to standing water in places not treated by the city’s contractor
- Clean gutters to allow proper drainage
- Clear storm drains to prevent standing water
- Stock ponds and basins with fathead minnows that eat mosquito larvae
- Change water in birdbaths at least weekly (twice a week in hot weather)
- Clean and maintain swimming pools
- Prevent boats from holding rain water. Store upside down, or sprinkle Bti* granules where water collects
- Ensure outdoor toys, playground equipment, and household items don’t collect water
*BTI contains spores that produce toxins that target mosquito larvae.
Monitoring West Nile Virus
The Larimer County Department of Health and Environment works with local mosquito control teams, cities, and Colorado State University to monitor mosquito trap data and assess the risk of West Nile virus (WNV) each week during the WNV season. This information is shared weekly on our website and helps guide decisions about mosquito spraying.
What is the Vector Index?
The Vector Index (VI) measures how many mosquitoes in an area are infected with West Nile virus. This number helps predict the risk to humans. The VI is based on the number of Culex mosquitoes (the type that carries WNV) and how many of them are infected. Studies have shown that when the VI is above 0.5, the risk of human infection increases.
Spraying for West Nile Virus Control
The decision to spray for mosquitoes to protect public health is based on WNV monitoring in mosquitoes. Public health officials recommend spraying when the risk index (VI) exceeds 0.5, as this is when human cases are more likely.
In Fort Collins, spraying is considered only when the risk index reaches 0.75 or higher, based on city policy. Since it can take up to 4 weeks to confirm human cases after infection, spraying is based on high numbers of infected mosquitoes, not human cases.
If spraying occurs, it will target areas with the highest risk of West Nile infection.
Nuisance Mosquitoes
Many mosquitoes are considered "nuisance mosquitoes," meaning they are a bother but do not carry the virus. The number of infected Culex mosquitoes varies each week in different areas. We track this using weekly trap data. Sometimes, an increase in nuisance mosquitoes doesn’t mean there is a risk of West Nile virus. We monitor mosquito populations with our control contractors every week.
Private Spraying
Some cities, towns, homeowner associations (HOAs), and businesses may choose to spray for mosquitoes, both for nuisance control and to reduce the risk of West Nile virus. These efforts are separate from the county’s activities.
Spraying by Homeowner Associations and the County
HOAs may decide to spray in their neighborhoods, independent of city or county actions. If an HOA requests spraying, they cover the cost, and we coordinate with them to prevent double spraying in the same area. Colorado Mosquito Control works with HOAs to ensure the spraying schedule is well-managed.
Mosquito Control on County Land
Currently, there is no funding for broader mosquito control efforts in Larimer County. If voters decide to fund a mosquito control district, that could change. For now, mosquito control efforts focus on population centers, and municipalities like Windsor, Timnath, Loveland, and Fort Collins cover the cost of spraying.
Notifications About Spraying
Fort Collins offers a text alert service to notify residents about spraying. To sign up, simply text "FCWNV" to 888-777 to receive updates by text.
Larimer County does not currently run its own mosquito control program. However, many local cities work with Vector Disease Control International (VDCI) to manage mosquito control in their areas. We are fortunate to partner with VDCI to help monitor and control mosquitoes in Larimer County. VDCI runs a local mosquito surveillance program. They map possible mosquito breeding sites and use light traps to track mosquito activity throughout the season.
If you see standing water, please report it to the appropriate contact below, depending on your location.
- Loveland: 970-278-9977
- Fort Collins: (866) 691-3987
- LaPorte (southern area only): (866) 691-3987
- Timnath - (877-276-4306) VDCI vendor - see Timnath.org mosquito control
- Windsor: 970-674-5400 - see Windsor.gov mosquito control
- Wellington: 970-568-3381
- Berthoud: 970-278-9977
- Unincorporated Larimer County: Call either (866) 691-3987 or 498-6775 to determine if you are within the City of Loveland's or City of Fort Collins' Larval Control Buffer Zone
Choosing a Mosquito Repellent
When picking a mosquito repellent, look for one that is proven to work against mosquitoes that carry West Nile Virus. DEET, Picaridin, Oil of Lemon Eucalyptus (also called PMD), and IR3535 are all good choices. Find the one that works best for you.
Cautions
- Apply repellent only to exposed skin—never under clothing.
- Don’t use repellent on cuts or irritated skin.
- Avoid applying it near your eyes and mouth.
- Keep repellents out of children’s reach. Never let children apply repellent.
- Don’t spray repellent indoors.
- After being outside, wash the repellent off your skin thoroughly.
- Follow the instructions on the product label.
- Don’t use too much repellent. Apply only what you need.
- Don’t use a product that combines sunscreen and repellent. Sunscreen needs to be reapplied more often than repellent, so using a combined product may result in overuse of repellent.
Repellent for Children
- Always read the label to see if the repellent is safe for children.
- Follow the instructions for children’s use.
- Avoid applying repellent to your child’s eyes, mouth, or palms.
- If your child sucks their thumb or puts fingers in their mouth, don’t apply repellent to their hands.
- An adult should always apply repellent to a child.
- Keep repellents out of reach of children.
- Use only the amount recommended for your child. Don’t over-apply.
- Don’t use products that combine sunscreen and repellent. However, using separate sunscreen and repellent is fine.
- If your child develops a rash or allergic reaction from repellent, stop using it, wash it off with mild soap and water, and contact your local poison control center.
Avoid Using:
- Repellents with more than 30% DEET on children.
- Oil of Lemon Eucalyptus on children under three, as it hasn’t been well-tested on young children.
- Repellent on infants younger than two months.
DEET Expiration
DEET is very stable and remains effective for a long time. The federal government doesn’t require an expiration date, but after about three years, the product’s appearance, smell, or feel may change. This doesn’t affect its effectiveness, but it might make it less pleasant to use. If you’re unsure about your product, contact the manufacturer.
Caring for Yourself if You Have West Nile Virus (WNV)
West Nile virus (WNV) is diagnosed with a blood test, but the test usually won't show a positive result until about a week or more after you start feeling sick.
The test checks if you have antibodies to WNV. These antibodies develop as your body fights the virus, and having them means you're unlikely to get infected again. The test can also help rule out other illnesses that have similar symptoms.
For mild to moderate WNV illness, people often recover on their own and don’t always need medical care, though you may choose to see a doctor if you feel it’s necessary.
Seek Medical Attention Right Away If:
- You have severe symptoms, like intense headaches or confusion.
- You develop symptoms of severe WNV illness, which can include encephalitis (swelling of the brain) or meningitis (inflammation of the lining of the brain and spinal cord).
- Pregnant or nursing women should contact their doctor if they develop symptoms that could be WNV.
What to Expect During Your Illness
If you have WNV, symptoms can appear 3 to 14 days after being bitten by an infected mosquito.
- Up to 30% of people will have West Nile Fever, which feels like the flu or mononucleosis (mono).
- Most people who are infected have mild or no symptoms.
- About 1 in 150 infected people will develop severe illness, such as encephalitis or meningitis. Symptoms of severe illness can include fever, fatigue, muscle weakness, confusion, tremors, and paralysis.
How to Care for Yourself:
- Drink plenty of fluids.
- Treat headaches and muscle pain with over-the-counter pain relievers (like aspirin or ibuprofen) as directed. Be sure not to take more than the recommended dose. If your pain isn’t relieved, consult your doctor.
- Rest to help your body recover. You may need time off from work.
- Not getting enough rest or fluids may cause symptoms to last longer or return.
Currently, there is no vaccine or cure for WNV in humans.
When to Call Your Healthcare Provider:
- If you have a severe headache, a stiff neck, or a high fever (over 103°F).
- If you have severe pain, confusion, tremors, convulsions, muscle weakness, or paralysis.
- If you’ve been vomiting for two or more days or can’t keep fluids down.
- If you haven’t improved after 3-6 days.
Blood Donation
If you have had West Nile Virus, do not donate blood or organs until you’ve fully recovered. People who have tested positive for WNV should wait at least 120 days from the start of symptoms or the date of their diagnosis (whichever is later) before donating blood. All donated blood is tested for active West Nile virus infection.
Link to Surveillance Data Map Local Spray Schedule
Larimer County works with the local cities and towns to monitor West Nile Virus.
Trap data helps the Larimer County Department of Health and Environment monitor the culex mosquito count in the area. Culex mosquitoes can carry West Nile Virus, so watching these numbers help recognize risk in the area.
West Nile Virus and Pets
Pets like dogs, cats, birds, horses, and alpacas can get West Nile virus from mosquito bites. Most pets that get infected with West Nile virus won’t show symptoms or will only have mild symptoms and will recover fully. Dead birds do not spread the virus to pets that come into contact with them. There is no evidence that pets can spread West Nile virus to humans.
Protecting Horses
West Nile virus can cause serious illness in horses that are not vaccinated, and up to one-third of unvaccinated horses may die from it. To protect your horse, make sure they are vaccinated against West Nile virus. Horses need two vaccinations, given three to six weeks apart, to be fully protected. Horses that are already vaccinated need a booster shot once a year. Talk to your veterinarian about vaccinating your horses against West Nile virus.
