FORT COLLINS, Colo. (CBS4) — West Nile Virus is spreading rapidly through the mosquito population in Northern Colorado, and experts from at least two counties fear it could soon infect humans as well. West Nile testing throughout Larimer and Weld counties in recent weeks has shown an increase in positive tests in mosquito traps. In Fort Collins, the positive cases have increased dramatically in recent weeks.

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“The infection rate is drastically increasing right now,” said Matt Parker, Natural Area Supervisor for Fort Collins.

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Parker said the City of Fort Collins has 53 traps spread throughout the area. Two weeks ago only two of the 53 traps showed positive results for West Nile.

“This week we’ve had 11 of our 53 traps test positive,” Parker said.

The issue isn’t unique to Larimer County, as Weld County has been reporting positive tests in mosquitos for weeks.

“The community should always have concern,” Parker told CBS4’s Dillon Thomas. “West Nile is in our region every year.”

Weld County has been spraying populated areas with a chemical used to kill the two main species of mosquitos that carry the virus. Fort Collins started their first series of spraying on Thursday night.

Parker said Fort Collins would focus their spraying on the southeast corner of the city near Harmony and I-25 where most of their concerning testing results have originated.

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One night of spraying, also known as “fogging,” can kill 50% of infected mosquitos. A second night of spraying, scheduled for Sunday, should handle most of the rest in the area.

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“So if you see that coming through your neighborhood, go inside and close windows. About an hour or so after the trucks up past that application has settled and you’re free to open windows,” Parker said.

Parker encouraged people to avoid outdoor activities at dusk and dawn. Infections can be prevented by wearing long sleeves and pants, by applying mosquito spray and by dumping out buckets that may have stagnant water.

For those in Fort Collins, the fogging trucks can be tracked on a live map here: http://www.fcgov.com/westnile

While most think of mosquitos when it comes to the transfer and spread of West Nile, Parker said the bird population is often the greatest spreader. Mosquitos infect birds who then carry the virus throughout the region.

Parker said mosquitos are also greatly capable of spreading the virus wide, underscoring the importance of each region addressing the issues for their neighbors.

“Mosquitos can fly great distances. They can fly multiple miles a night,” Parker said.

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With global warming rising the average temperature throughout the world, some say mosquito seasons will continue to grow in length.

Parker said Coloradans should continue to be cautious of West Nile Virus until the weather cools off.

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“We’re really going to start looking for 50 degree overnight lows. That’s the temperature that really slows down the biological reproduction cycle,” Parker said.

Dillon Thomas