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BERTHOUD, Colo. — Larimer County officials reported Thursday the first positive sample of mosquitoes with West Nile virus in the county and in Colorado this year.

The infected mosquitoes were trapped last week in Berthoud.

The county health department said more infected mosquitoes will likely be found in the area in the coming weeks because hot weather speeds up mosquito and virus reproduction.

West Nile virus is transmitted most frequently during July and August.  Symptoms range from none to severe illness.

About 25 percent of people infected will develop West Nile fever. The Larimer County Health Department is working with cities to monitor and assess the risk to residents.