DENVER (CBS4) – Health departments in Colorado are saying that the mosquito population is average right now, but in some areas the mosquitoes that carry the West Nile virus are up 25 percent.

Mosquitoes in Denver and Larimer counties have tested positive for the virus, and some precautionary measures are now being taken. Workers in several cities are trapping and testing mosquitoes, and some spraying to kill the insects is taking place.

The state also reported this week that it has its first case of the virus this year. A man in Mesa County was diagnosed, but so far no information has been released about his condition.

LINK: FightTheBiteColorado.com

In many Front Range towns spraying to kill mosquitoes is triggered if the number of the insects in traps hits a critical mass or if a neighboring community catches a West Nile carrier.

Health officials are warning the public and asking them to remember what they call the four Ds:

– Use bug spray with deet.

Dress in long sleeves and pants.

– Avoid being out at dusk and dawn.

Drain all standing water.

Mosquito season can last until the first hard freeze of the year, which is generally sometime around Oct. 1.