Colorado State Reportable Tick-Borne Diseases

There are over 20 tick-borne diseases/conditions currently known to occur throughout the US and that may impact Colorado residents and/or their pets at home or through travel.

However, many tick-borne diseases that occur within the US in both humans and pets are not reportable within Colorado, so incidence and prevalence is difficult to monitor. The Colorado Department of Health and Environment has stated that “since so many of these diseases manifest as febrile illness with a non-specific constellation of symptoms that, yes, we believe they are routinely under reported. However, we believe that is because they are difficult to diagnose.” Reporting also depends on laboratory capabilities, which are unreliable or unavailable in some cases, as well as compliance with Regulation 6 CCR 1009-1, which are the rules and regulations pertaining to epidemic and communicable disease control.

Tick-Borne Diseases required to be reported by Physician or Laboratory, Colorado Department of Public Health and Environment as of March 2026 include:

• Colorado Tick Fever
• Lyme disease (Borrelia burgdorferi)
• Q-Fever (Coxiella burnetii)
• Rickettsiosis (Spotted fever rickettsiosis, including Rocky Mountain spotted fever)
• Tick-Borne Relapsing Fever (Borrelia species and Spirochetemia except burgdorferi species)
• Tularemia (Francisella tularensis)
• Powassan virus disease (Arboviral Diseases-known arthropod-transmitted viruses)

*As of March 2026, Colorado Tick Fever, Lyme (B. burgdorferi), Q-Fever, Rickettsiosis, and Powassan Virus, are now required to be reported only by laboratories. Tick-Borne Relapsing Fever and Tularemia are required to be reported by both laboratories and medical care providers, facilities, veterinarians, and additional reporters.

Surveillance in Colorado

Surveillance of both ticks and tick-borne diseases is limited in the state of Colorado. Zoonotic diseases reported in Colorado from 2018-2023 can be viewed here. However, not all of the nationally notifiable tick-borne diseases are tracked or nor reported by the Colorado State Department of Health & Environment (CDPHE), leaving incidence of infection for many tick-borne diseases unknown in Colorado.

Very small and limited active tick surveillance studies have been historically conducted in CO. And only limited passive surveillance of ticks had been conducted by the CDPHE until 2026. CDHPE launched a statewide active tick and tick-borne disease surveillance program in 2026, with 27 counties participating this first year. Data collected will be entered into VectorSurv once pathogen results have been reported from the CDC. Active tick and tick-borne disease surveillance will help to fill the gaps of knowledge and provide improved monitoring of tick species presence and distribution, as well as pathogen risks in Colorado.

Results from 2014-2019 passive tick surveillance for the most commonly encountered ticks in Colorado are displayed here. Interestingly, the CDPHE has mapped the occurrence of the Lonestar tick in Colorado, though it is not yet known to have an established natural population in the State. Data that was collected regarding lesser encountered tick species, some with both veterinary and medical significance, are not displayed. Ticks conventionally regarded as “non-human biters” were not identified by species in the 2012-2016 CDPHE tick data set, though research indicates that some of these species may pose a bigger risk to human health then previously considered. There is much unknown about the occurrence of ticks species and their pathogens in Colorado. The CDPHE passive tick surveillance program is active again. Public submissions for tick identification only can be made through Colorado Citizen Scientist Tick Submission Form.

The CDC reports 64 cases of Lyme disease in Colorado between 2008-2023, with 2023 showing the highest annual case count at 32. The Colorado Department of Public Health and Environment (CDPHE) states that none of the exposures originated in Colorado, however reports of Lyme disease have increased in the past few years. CDPHE shows only 10 cases of Lyme disease between 2018-2023, stating “Lyme disease investigations were on hold due to limited capacity during the pandemic.” However, the new Colorado Reportable Disease Data interactive database provides an overview of Lyme disease that healthcare providers and laboratories are required to report to public health in Colorado, and this data shows 40 cases of Lyme disease reported in 2024.

The CDC states there are limitations of surveillance data and problems with under-reporting for Lyme. This underreporting is also an issue with other tick-borne diseases.  A recently released estimate by the CDC based on insurance records suggests that each year approximately 476,000 Americans are diagnosed and treated for Lyme disease.

Surveillance in Colorado Dogs

Positive cases of Lyme, Anaplasmosis, and Ehrlichiosis in dogs have been documented in Colorado as shown in prevalence maps compiled by the Companion Animal Parasite Council (CAPC), and the cases for each of these diseases have increased annually. Veterinarians interested in participating in this surveillance effort should contact CAPC. More here.