Health

West Nile Virus

What is West Nile virus?

West Nile virus is a disease that spreads through mosquito bites. It is common in Colorado and occurs every year. The largest outbreak of West Nile virus in Colorado occurred in 2003, with over 2,800 reported cases and 63 deaths. Some people who became seriously ill are still recovering and some have permanent disabilities. Infected mosquitoes have been found in Larimer County every year since then.

How is it Spread?
West Nile virus is spread to people through the bites of infected mosquitoes. You cannot get the virus from another person. People can get West Nile virus during mosquito season which starts in the summer and continues through fall.

Symptoms of West Nile Virus
Symptoms can appear 3 to 14 days after being bitten by an infected mosquito.

  • No symptoms in most people. Most people (8 out of 10) infected with West Nile virus do not develop any symptoms.
  • Mild illness: About 1 in 5 people infected with West Nile virus develop a fever with other mild symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash. Most people with mild illness due to West Nile virus recover completely, but fatigue and weakness can last for weeks or months.
  • Severe illness: About 1 in 150 people infected with West Nile virus develop serious symptoms including high fever, headache, neck stiffness, stupor, disorientation, tremors, muscle weakness, vision loss, numbness, coma, and paralysis. Recovery from severe illness may take several weeks or months. Some effects to the central nervous system might be permanent.

Diagnosis and Treatment
If you think you or a family member might have West Nile virus, talk with your healthcare provider. Healthcare providers diagnose West Nile virus infection based on symptoms, history of possible exposure, and a blood test. Learn more about diagnosis and treatment at www.cdc.gov/west-nile-virus/symptoms-diagnosis-treatment/index.html

Who is at risk?

Even if you don't get bitten by mosquitoes often, some groups are at higher risk for serious symptoms.

People Ages 55 and Older
Severe illness can occur in people of any age. However, people ages 55 and older are at greater risk. About 1 in 50 people ages 55 and older develop severe illness if they are infected with West Nile virus.

People With Certain Health Conditions
People with health conditions such as cancer, diabetes, and hypertension, and those who have had organ transplants or are taking medications that suppress the immune system are also at higher risk for severe illness. 

How to Prevent West Nile Virus

The best way to avoid West Nile virus is to prevent mosquito bites. The more you make mosquito bite prevention part of your summer routine, the easier it will feel - and the more you'll be protected against West Nile virus.

Establish your prevention routine:

  • Regularly use EPA-registered insect repellent before going outside.
  • Wear loose-fitting, long-sleeved shirts and pants for long walks, gardening, and other time outside.
  • Avoid scheduling outdoor activities during peak biting times around dawn and dusk. 
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Protection takes planning. Make a plan to protect yourself and your family from mosquito bites that can spread West Nile virus during the summer.

  • Store EPA-registered insect repellent near your front or back door to easily use it.
  • Regularly use your insect repellent before going outside.
  • Note when you need to buy more insect repellent.
  • Carry travel-sized insect repellent or wipes.
  • Have loose-fitting, long-sleeved shirts and pants ready to wear for long walks, gardening, and other time outside.
  • Avoid scheduling outdoor activities (e.g., playdates, gardening, or exercise classes) when mosquitoes are most active around dawn and dusk.
  • Drain standing water in your yard at least once a week.
  • Install or repair screens on windows and doors to keep mosquitoes outside.
  • If possible, use air conditioning to keep doors and windows closed.

Choosing a Mosquito Repellent

When picking a mosquito repellent, look for ingredients that are proven to work against mosquitoes. 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.

West Nile Virus and Pets

Pets like dogs, cats, birds, and alpacas can get West Nile virus from mosquito bites. Most pets that get infected with West Nile virus have mild or no symptoms and recover completely. 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.


Mosquito Control Information

Learn more about mosquito monitoring and spraying: larimer.gov/mosquito-control-information