(CBS4) – After weeks of growing concerns of West Nile virus spreading among the mosquito population in northern Colorado, Larimer County health officials have identified human cases of the virus.

CBS4’s Dillon Thomas has learned at least three people have tested positive for West Nile virus in northern Colorado in the past week.

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Natural resource experts in Fort Collins say they spread of the virus among the mosquito population is “drastically increasing” as of late. In Fort Collins alone the mosquito population has seen the virus spread five times its original size in just recent weeks.

Matt Parker, Natural Areas Supervisor for the City of Fort Collins, said two of the city’s 53 mosquito traps tested positive for West Nile two weeks ago. In their recent test this week 11 of the 53 traps tested positive. Most of those that tested positive were in the southeast corner of the city, predominantly west of I-25 and north of Harmony.

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Fort Collins started spraying, also known as “fogging,” the area to kill off infected mosquitos Thursday night. Weld County has been spraying areas of concern for several weeks as the issue continues.

West Nile virus is predominantly spread by two specific species of mosquito. The virus largely travels between the mosquito and bird populations, and in rare cases can be transferred to humans.

Thousands of Coloradans have tested positive for West Nile since official tracking began years ago. More than 140 Coloradans have died as a result of the virus. A significant majority of those infected are able to fight the virus away from a hospital, though some need emergent medical treatment.

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Experts say people can avoid contracting West Nile virus by wearing long sleeves and pants, dumping out buckets of water that may be sitting around, avoiding outdoor activities around dusk and dawn and also making sure to apply repellent.

Dillon Thomas