West Nile virus (WNV) is a disease transmitted to humans by mosquitoes. It first appeared in the U.S. in 1999 in New York. It has since traveled westward across the U.S. and now is in Colorado.
Although all age groups are at risk for WNV, individuals over the age of 50 and those with compromised immune systems have the highest risk of severe disease. WNV can be fatal to anybody, regardless of age or health. We want you to have the facts, in order to ease your fears, so that you can take appropriate prevention measures.
The virus is carried long distances by infected birds and then spread locally by mosquitoes that bite these birds. The mosquitoes can then pass the virus to humans and animals, primarily birds and horses. There is a vaccine for horses, but none for humans. House pets do not spread the illness.
Health departments across the state are closely monitoring human and horse illnesses and tracking the virus by testing dead birds and trapping mosquitoes.
Mosquito season in Colorado starts in the spring and ends in mid-September.
Less than one percent of mosquitoes carry this virus and fewer than one percent of people infected with the virus will develop severe illness. Symptoms generally appear 3 to 14 days after exposure. All residents in areas where West Nile virus activity is confirmed are at risk, but people over age 50 seem to be especially vulnerable to the severe forms of disease. In rare cases, it can be fatal.
West Nile virus can cause encephalitis (swelling of the brain) and/or meningitis (swelling of the brain's lining).
Most infections are mild and symptoms include:
More severe infections may include:
Persons with these symptoms need to seek medical attention immediately.
Information provided by Fight the Bite Colorado.