West Nile Virus
How it is spread
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.
Taken from Fight the Bite Colorado