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Tick on a person

Study Finds Disease-Carrying Tick Populations are Expanding into Colorado

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Written by CSU MarComm Staff on November 4, 2022

Adapted from a news release by Bay Area Lyme Foundation

Ticks capable of carrying diseases like Rocky Mountain spotted fever, Colorado tick fever and tick-borne paralysis pose an emerging threat in Colorado, according to a recent study led by Colorado State University researchers.

The study, funded by the Bay Area Lyme Foundation, showed that American dog ticks are present in 16 counties in Colorado where they were not previously identified by the Centers for Disease Control and Prevention. Rocky Mountain wood ticks were found in 38 of the 64 Colorado counties, whereas they had previously only been identified in 33 counties.

With the help of the public who sent in ticks for testing, the researchers quantified current county-level distribution of Rocky Mountain wood ticks, Dermacentor andersoni, and American dog ticks, Dermacentor variabilis. Ticks collected by citizen scientists were evaluated at Northern Arizona University as part of the Bay Area Lyme Foundation’s Free Tick Testing program.

“It was interesting to us to see American dog ticks in unexpected counties in Colorado, which appear to be invading from nearby states or traveling with people and pets. And also to show that Rocky Mountain wood ticks appear, for the most part, to inhabit counties at higher elevations than American dog ticks,” said co-author Daniel Salkeld, research scientist in CSU’s Department of Biology. “This study is a red flag that, on the county level, it is necessary to increase tick surveillance locally, and, on an individual level, to take precautions and know the symptoms of tick-borne diseases.”

Ticks found on humans and dogs

Rocky Mountain wood ticks and American dog ticks are both known carriers of Rickettsia rickettsii, which causes Rocky Mountain spotted fever, a disease that is on the rise in the U.S. These ticks also carry Francisella tularensis, which causes tularemia, a potentially life-threatening disease that has seen a spike in incidence in recent data and can cause tick-borne paralysis.

According to the study, both species of tick were found on humans and dogs. Rocky Mountain wood ticks appear to be more attracted to humans, with this tick representing 58% of ticks attached to humans, compared to the American dog tick, which represented 92% of ticks attached to dogs.

“The citizen science approach has been critical to supporting our efforts, as widespread active surveillance programs in Colorado have had difficulty due to the state’s diverse terrain, and no Colorado counties regularly conduct these,” said lead author Elizabeth Freeman, a graduate of  the Colorado School of Public Health Master’s in Public Health program. “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.”

Tick collection by citizen scientists

Citizen scientists collected and provided the ticks evaluated in the study as part of the Bay Area Lyme Foundation’s Free Tick Testing program, which collected more than 20,400 ticks, of which 8,954 are Ixodes ticks capable of carrying the most common tick-borne pathogens. This new study expands on previous research identifying ticks capable of carrying Lyme and other tick-borne diseases in 83 counties (in 24 states) where these ticks had not been previously recorded. Some of the new county reports are likely due to travel-associated exposures (e.g., Montana), but many counties, such as those in Colorado, are in close proximity to previously known locations, illustrating either spreading range of ticks or the need for expanded on-the-ground surveillance.

The research was conducted through a partnership between Bay Area Lyme Foundation, CSU, Northern Arizona University and the Translational Genomics Research Institute (TGen).

Interactive maps show the distribution by county of the tick species collected, including western blacklegged ticks, blacklegged ticks, American dog ticks and lone star ticks. Prevalence of Rocky Mountain wood ticks in this study were not previously evaluated and reported.

Ticks sent to the initiative from January 2016 through August 2019 were tested free of charge. These data were categorized, mapped and recorded, as well as provided to the submitter. Ticks were submitted from every state except Alaska. The program received a six-fold increase in tick submissions over initial estimates.

This story was originally written for CSU Source.