West Nile virus is most commonly spread by infected mosquitoes and has been regularly reported in Colorado since 2002. The risk to humans occurs primarily from June through early September when mosquitoes are most active. However, Colorado often continues to see West Nile virus reports through the month of October when lower temperatures cause mosquitoes to go dormant until spring.
Anyone living in an area where West Nile virus is present in mosquitoes can get infected. The risk of infection is highest for people who work outside or participate in outdoor activities, because of greater exposure to mosquitoes.
The time between when a person gets bitten by an infected mosquito to when they experience symptoms is usually two to six days but can be up to 14 days. Most people who are infected with West Nile virus will not have any symptoms. About one in every five people infected with West Nile virus will develop an illness that may include headache, muscle aches, joint pain, rash, or gastrointestinal symptoms. Older adults and those who are immunocompromised are at increased risk of more severe infection. Talk with a health care provider if you experience new or worsening symptoms of illness, including severe headaches or confusion.
Treatment for West Nile virus
There is no treatment for West Nile virus infection, but milder illness usually improves on its own. Prevention is key, especially for people at higher risk. Rest, fluids, and over the counter pain medications may relieve some symptoms.
To protect yourself:
- Use insect repellents when you go outdoors. Repellents containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus, as well as para-menthane-diol products provide the best protection. For more information about insect repellents visit the EPA’s information webpage. Follow label instructions.
- Limit outdoor activities at dusk and dawn. That is when mosquitoes that carry West Nile virus are most active.
- Wear protective clothing (loose-fitting long pants, long-sleeved shirts, and socks) in areas where mosquitoes are active. Spray clothes with insect repellent for extra protection.
- To mosquito-proof your home: Drain standing water around your house at least once a week. Empty water from tires, cans, flowerpots, clogged gutters, rain barrels, birdbaths, toys, and puddles.
- Install or repair screens on windows and doors.
How do people get infected with West Nile virus?
Most people get West Nile virus from the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the virus to humans, birds, and other animals such as horses.
Who is at risk for infection with West Nile virus?
Anyone living in an area where West Nile virus is present in mosquitoes can get infected. Colorado has had cases of West Nile virus every year since 2002. The risk of infection is highest for people who work outside or participate in outdoor activities, because of greater exposure to mosquitoes.
People of any age can get West Nile virus. However, people older than 60 years are at the greatest risk for severe disease. People with certain medical conditions such as cancer, diabetes, hypertension, kidney disease, and people who have received organ transplants are also at greater risk for serious illness.
What are the symptoms of West Nile virus?
Most people infected with West Nile virus don't get sick. For people who do, the time between the mosquito bite and the start of symptoms can be from two to 14 days. In rare cases, the virus can cause a serious brain infection such as meningitis or encephalitis. These infections begin suddenly with high fever and headache and may progress to stiff neck, disorientation, tremors, and coma. Severe infections can result in permanent brain damage or death. Most deaths occur in people older than 50 years. There is no treatment for West Nile virus infection, but milder West Nile Virus illness usually improves on its own. Prevention is key, especially for older adults and people with immunosuppressing medical conditions at higher risk of severe illness. Rest, fluids, and over-the-counter pain medications may relieve some symptoms.
If you think you or a loved one is sick with West Nile virus, talk with a health care provider.