City to spray pesticides to prevent West Nile Virus threat

Seth Bodine

With an increased risk of the West Nile Virus, the city of Fort Collins and the Larimer County Health Department will be spraying pesticides in an effort to minimize the threat. The spraying will occur on August 24 and 28 from 8 p.m. to 2 a.m. each night.

Colorado Mosquito Prevention will be spraying pesticides in the areas outlined on the map on August 24 and 28 from 8 p.m. to 2 a.m. on each night. (Photo courtesy of City of Fort Collins)



According to Katie O’Donnell, Public Information Officer for Larimer County Department of Health and Environment, the threshold for infected culex mosquitoes – mosquitoes that are carriers for the virus – has been reached. O’Donnell said that the threat index is calculated by Colorado State University every week, and the city of Fort Collins will consider spraying at an index of .75.

This week, the index was at .93.

Dr. Broox Boze operations manager for Colorado mosquito control said that trucks will be driving around areas with infected culex mosquitoes with a light mist of permethrin-based pesticide. Boze said they use it because it’s the safest pest ingredient in the market, and can be found over-the-counter.

“The way which we apply it, it kills only mosquitoes,” Boze said.

O’Donnell said that the pesticides are not harmful to humans because of the amount put in the air regulated by Environmental Protection Agency set standards. However, she recommends that residents in the area stay inside with window closed for 30-60 minutes after the spraying.

“These chemicals have been used for a very long time, in very small dosage,” O’Donnell said. “Obviously, if you’re going to use more than the recommended amount it could be a not good situation for human health. We definitely look at risk. So when our West Nile infected population is low, we’re not going to spray because we don’t want to even put anything into the air if we don’t have to. So it’s a balance for us.”

According to Boze, pesticides are an effective way of preventing West Nile Virus and there is usually a 75-85 percent knockdown after the first fogging, and the second application aims for 90 percent.

“With vector-borne diseases, anything that is transmitted by a mosquito, the best way to break the transition cycle of the disease is to get rid of the mosquitoes,” Boze said. “So fogging absolutely helps breaks that life cycle of the virus.”

Boze said that the threat of West Nile is typically greater in the eastern area of the city.

“It varies from year to year, and we’re constantly analyzing to see where the mosquitoes are most active or most abundant,and where the virus is most active and we target those areas specifically,” Boze said.


O’Donnell said Larimer county is among the top ten counties in the country for the risk of West Nile virus. O’Donnell said that different mosquitoes can survive in different climate, and the Culex mosquito is the one that can survive over the winter because they hibernate.

“There’s a lot of speculation on why that is,” O’Donnell said. “Some of it, it’s probably just be the weather pattern, the fact that we can have mosquitoes over the winter season, and then we have a lot of irrigation and farmlands that is very difficult to treat.”

O’Donnell said that while some people believe that spraying is unnecessary due to the low amount of reported cases, a lot goes unreported.

“A confirmed blood test is the only time that my office gets a reported case. It really is in the community,” O’Donnell said.

According to the Center for Disease Control and Prevention, there is no cure for the West Nile Virus.

“While some people don’t get sick, some people get really, really sick and it has very long-lasting effects. Doesn’t matter if you are healthy before that or not. So, protect yourself.”

Collegian News Editor Seth Bodine can be reached at or on Twitter @sbodine120.