Fort Collins canceled mosquito spraying planned for Wednesday after trap data indicated the rate of West Nile virus-infected mosquitoes in the spray area has significantly declined.

The city had planned to spray an area of north and central Fort Collins on Sunday and Wednesday nights to combat the risk of West Nile virus, but spraying was halted early Sunday because of rain. Wednesday spraying was planned for 8 p.m. to 2 a.m. But trap data reported Monday found a significant drop in the spray area’s vector index, a calculation that conveys the rate of mosquitoes infected with West Nile virus in an area.

The vector index dropped from 0.75 (the city’s threshold for spraying) to 0.06 in a single week, said Matt Parker, a senior supervisor in Fort Collins’ natural areas department.

Parker said the swift decline was surprising given continued warmer-than-usual overnight temperatures, although evenings have cooled down during the last several days.

Larimer County’s Department of Health and Environment rescinded its recommendation for spraying after the new data was released, so Fort Collins leaders called off spraying, city spokesperson Amy Resseguie said.

The planned spray area’s boundaries included:

• Douglas Road, Shields Street, Vine Drive and Timberline Drive
• Vine Drive, College Avenue, Drake Road and Timberline Road
• Laurel Street/Elizabeth Street, Overland Trail, Drake Road and College Avenue

The city’s contractor, Vector Disease Control International, carried out spraying of the permethrin-based product in about one-third of the targeted area on Sunday. The areas sprayed were in the north end of the spray area as well as the southwest and southeast corners.

Spraying began about 8:20 p.m. and continued off and on until 11:45 p.m., Resseguie said. She said trucks stopped spraying every time it started to rain in the area and continued once the rain passed, but shortly before midnight, it became clear the rain wasn’t going to let up in time to finish spraying.

Some community members objected to the decision to spray despite intermittent rain, citing permethrin’s extreme toxicity to aquatic life and its potential to reach storm drains.

The EPA-approved label for the product Fort Collins uses, Aqua-Kontrol 30-30, doesn’t specify whether it can be used during rain but does say users should make sure it doesn’t enter any drains during or after application.

The label specifies not to apply “directly into sewers or drains.”

“That word ‘direct’ is very important,” Parker said. The city’s application method is “not the same as directly spraying a storm gutter or making an application within the sewer system.”

Safety concerns

Permethrin is toxic to bees and considered a likely human carcinogen when ingested, according to the EPA. It can also remain on the leaves of plants for 1 to 3 weeks, according to the National Pesticide Information Center.

Those health and environmental concerns have led some people to call for curtailed spraying.

City Council member Ross Cunniff, the only council member to vote against a policy change that lowered the bar for mosquito spraying last year, said he’s concerned the city doesn’t do enough to notify people about spraying and also worries spraying could increase the number of human cases in an area by giving people a false sense of security and inspiring them to forgo insect repellent.

“Given that we’re not having, in my opinion, a significant positive impact on public health by spraying and are having a significant environmental impact by spraying, then I really think we should reevaluate our spraying program,” he said.

But Parker said the city’s chosen permethrin-based spray is “widely recognized as one of the best widespread adult mosquito treatment products available.”

“When applied in a manner consistent with the label, it doesn’t seem to pose health concerns,” he said. “There are a lot of materials that, if ingested, can cause you significant issues, but that’s not how they’re intended to be used.”

He added that mosquito spraying is just one part of the city’s efforts to combat West Nile virus, which in its rare neuroinvasive form can be deadly. The city treats mosquito larvae-producing sites weekly to prevent the spread of infected mosquitoes.

How the city decides when to spray

Residents also took issue with the geography of the spray area. Fort Collins divides city limits into four “spray zones” and reports vector indices for each quadrant on the city website. But city leaders don’t use those values to decide whether to spray. Instead, the city typically sprays in any area where five consecutive traps meet the 0.75 threshold for spraying.

That approach resulted in spraying in two quadrants of Fort Collins even though neither reached the 0.75 threshold. As of Monday, the vector indices by quadrant ranged from zero to 0.27.

Resseguie said the city reports the trap data by quadrant to give people a general understanding of what’s happening in each part of the city, but it targets smaller areas or areas that traverse multiple spray zones because mosquitoes don’t respect those boundaries.

“Years ago, what we could do was measured by quadrants, and recommendations were made based on the measure in the whole quadrant,” she said. “We’ve gotten better data and better ability to calculate those numbers. We’ve been able to focus on those smaller areas so that we can treat the smallest geographic area to still be effective.”

The city notifies community members about spraying by posting on Next Door, Facebook and other social media and sends out text, email or phone call notifications for residents who opt in. You can opt in for spraying notifications by texting FCWNV to 888-777. You can also sign up for alerts through Larimer Emergency Telephone Authority (LETA) 911.

Sunday was the first time the city has sprayed since City Council approved a policy change last year that lowered the bar for mosquito spraying. In a 5-1 vote, council removed the requirement that at least two human cases of West Nile virus had to be confirmed in a single week before spraying would take place. Staff said the human case requirement created a lag in response because it takes a few weeks for someone infected with West Nile virus to go on the books as a confirmed human case. Staff recommended lowering the vector index threshold from 0.75 to 0.5 because the 0.5 vector index means human West Nile cases are very likely, Parker said.

Council ultimately decided to keep the 0.75 threshold. Cunniff was the sole dissenting vote on the policy change that removed the human case requirement. Mayor Wade Troxell was absent.

Potential for change in policy

The council lineup has changed considerably since last year’s vote, though, with council members Susan Gutowsky, Emily Gorgol and Julie Pignataro replacing three people who voted yes on the current policy.

Cunniff said he plans to suggest changes to the city’s spraying policy at a future council meeting.

He added that any policy changes should also seek to prevent the spread of West Nile virus.

“West Nile virus, when it gets to its neuroinvasive form, is a terrible disease,” he said. “I don’t want to downplay that. But I also want to make sure we’re doing what is most likely to lead to fewer neuroinvasive cases while not damaging sensitive individuals and the environment.”

Fort Collins has had one confirmed human case of West Nile virus this season. About 80% of people who are infected do not show symptoms, and about 20% will develop West Nile fever. Less than 1% develop the more severe neuroinvasive form.

The West Nile virus season ends after the first overnight freeze.

Jacy Marmaduke covers government accountability for the Coloradoan. Follow her on Twitter @jacymarmaduke. 

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