When Carly Senst, the epidemiologist for Pitkin County, heard in late August that the county probably had its first-ever case of West Nile virus, she wasn’t exactly surprised. 

“It was more like, ‘Yep, all right, it’s happening,’” she said. 

That ‘it’ refers to the increase in diseases such as West Nile virus that are spread by mosquitoes or other carriers; Senst and other public health officials have expected to see more of these vector-borne diseases as a result of human-caused climate change. The discovery of the first probable case of West Nile comes just as the Pitkin County public health department has identified climate change as one of the area’s top health concerns. 

“Usually high-elevation places tend to not be affected by vector-borne disease,” Senst said. Conditions this summer are indicative of a climate that is becoming more hospitable to mosquitos and other vectors that can transmit diseases to humans. 

The limiting factor for diseases such as West Nile, which are carried by insects, has typically been Pitkin County’s cold nights. Senst said a wet spring and the warmer nights this summer have combined to create primer conditions for mosquitoes to live and breed here. 

The average low temperature in Pitkin County from May through July this year was warmer than the historical average, although 2018, 2020 and 2021 had higher average minimum temperatures, according to NOAA. Generally, average overnight lows in the early summer months are on the rise, data shows.

Senst said it’s likely that there was more standing water this summer as well, since a snowy winter and cool, wet spring kept snow in the high country long into the summer. 

“West Nile hadn’t come on our radar recently and this changes our risk assessment for which pathogens and which diseases we will prioritize into the future,” Senst said. 

Smoke muddies the view of Aspen’s ski mountains and hovers over the Aspen Golf Club in September 2020, near the end of a summer where wildfire-produced smoke waves harmed local air quality on no fewer than 16 days through the end of September. Poor air quality carries a host of health concerns, and as wildfires burn hotter and longer thanks to climate change, smoke events are expected to be more intense. Credit: Photo courtesy of Patrick Severy

Climate change brings new public health challenge

Pitkin County’s public health department hasn’t seen many “typical” seasons. The department was formed in 2017, and its first plan identified mental health, access to health care, housing, and water quality and quantity as top priorities.

When the COVID-19 pandemic hit in 2020, the department grew from four full-time positions to a peak of 30 employees. As the emergency has receded, there are now 16 full-time workers, several of whom are on an environmental health team that was previously a separate county department. Public Health Director Jordana Sabella said the growth falls within the department’s original plans for expansion, although those plans did not include the catalyst of a pandemic. Now, Sabella aims to apply lessons learned during the pandemic to day-to-day life.

“What we learned during COVID is that communication of information is critical,” Sabella said. Much of that communication now will focus on how climate change could affect people’s health. “Our community definitely understands that climate change is happening, but the connection to health is not the first thing many people think about.”

There are four key areas where a changing climate is likely to adversely affect health: rising temperatures, extreme weather, air quality and vector-borne illness. 

The recent discovery of a case of West Nile virus illustrates how county residents may expect to see more diseases as a result of the changing climate. The numbers of cases of West Nile virus in Colorado can vary widely from year to year, depending on conditions. Case numbers in Colorado were higher than average this year, with 208 known infections and 13 deaths. Many of those infections came earlier in the summer than in years past.  

West Nile virus is one of many vector-borne diseases that public health officials are watching closely. Ticks are a common carrier of Lyme disease and Rocky Mountain spotted fever, and a 2022 study from Colorado State University found that disease-carrying tick populations have expanded in the state. 

A 2016 survey by the Colorado Department of Public Health and Environment found Rocky Mountain wood ticks, which are carriers of bacteria that cause Rocky Mountain spotted fever, to be present in Pitkin County, as well as neighboring Garfield, Eagle and Gunnison counties, among 21 Colorado counties where the tick was identified. A 2022 study from Colorado State University found Rocky Mountain wood ticks in 38 Colorado counties, reflecting a growing tick population. Credit: Courtesy CDPHE

A 2016 survey by the Colorado Department of Public Health and Environment shows that Rocky Mountain wood ticks, which are carriers of bacteria that cause Rocky Mountain spotted fever, are present in Pitkin County, as well as neighboring Garfield, Eagle and Gunnison counties. 

The CSU study showed the presence of American dog ticks in 16 Colorado counties; the Centers for Disease Control and Prevention had previously not identified those ticks anywhere in Colorado. The study also found Rocky Mountain wood ticks in 38 Colorado counties, up from the 33 where the CDC found them. 

Senst said Lyme disease is not endemic to Colorado, but it is possible that there have been unidentified cases originating in the state. Pitkin County is required to report any cases tick-borne illnesses to the state. There have been instances of these vector-borne diseases turning up in Pitkin County in the past, but none were found to have been locally transmitted. 

“Pitkin County residents have contracted vector-borne illnesses, but we were unable to confirm where they contracted it due to travel,” Senst said. 

A key conclusion from the CSU study was the need for more extensive surveillance of tick species statewide. The county does not currently conduct local tick surveys. 

“With the knowledge that there is a risk of encountering both the Rocky Mountain wood tick and American dog tick in Colorado, there should be more motivation to further enhance surveillance studies to fully understand the public’s risk of disease,” lead author Elizabeth Freeman said in a news release.

And it’s not just ticks and mosquitos changing the public health picture thanks to climate change. Warming temperatures can bring changes in what plants survive and thrive in this area, and Kurt Dahl, environmental health manager with Pitkin County Public Health, said it’s likely that allergy season will extend. Then there’s the heat itself, which increases the risk of dehydration and heat stroke, and which can have smaller, harder-to-measure impacts. 

“We don’t have a lot of people with air conditioning in the valley,” Dahl said. “So, when it’s 80 degrees at night [in your home] and you don’t have AC, people lose sleep, and that impacts health.” 

A mountain biker rides Hummingbird Trail above Hunter Creek Valley on Sept. 10, while spots of snow linger on high mountain peaks from a wet spring. Warmer summer nights and more standing water in Pitkin County have created prime conditions for mosquitos that transmit diseases such as West Nile virus. Credit: Elizabeth Stewart-Severy/Aspen Journalism

More heat and drought also contribute to a higher risk of wildfire. Smoke from wildfires either close to home or hundreds of miles away can aggravate respiratory and cardiovascular illnesses and can pose a danger for high-risk groups such as infants and pregnant women. 

Pitkin County Public Health is looking to add an air quality specialist to focus specifically on the challenges that climate change brings to the area’s clean air. Neither the city of Aspen nor the county has such an expert on staff. 

“I think we’re missing a lot of opportunities because of that hole,” Dahl said.

An air quality specialist would advocate the county’s positions on state-level rules, regulations and legislation, and try to expand other local programs such as radon testing and mitigation. 

Radon is a cancer-causing gas that results from the breakdown of uranium in soil, rock and water; it enters homes through cracks in foundations, crawl spaces and basements, and it has been detected at potentially dangerous levels in 30% of households in Pitkin County. The county distributes free testing kits every January and encourages people to check their mitigation systems every three years. 

On the climate front, new expertise in the department would focus on improving communication with the public during wildfire smoke events; much of the county’s summer population does not live in the area year-round, and Dahl said it’s a challenge to effectively communicate with tourists about air quality and associated health risks.

Improving communication and helping the public make informed decisions about health are vital, and Dahl said it’s important to remember there are myriad reasons to reduce emissions. Carbon dioxide not only contributes to climate change but impacts health. 

As the effects of a warming climate are felt more frequently in daily life, Sabella said the public health goal is to help people make the best decisions in a changing world. 

“Our big focus is communicating that it’s not just about the polar bears and the penguins. It’s also about our health,” Sabella said. “We will continue to make the connection with the public about why we’re interested in climate change, why it is something that is going to touch us all.”

Aspen Journalism, which is solely responsible for its editorial content, is supported by a grant from Pitkin County’s Healthy Community Fund. 

Elizabeth Stewart-Severy is a freelance journalist based in Snowmass Village. She grew up in Aspen and has worked as an editor at Aspen Journalism, reporter at Aspen Public Radio and an English and journalism...