Ticks at High Altitudes: Expanding Risk for Lyme Disease

Ticks are expanding into new environments
Higher altitudes were once considered low risk
That assumption may no longer hold

Ticks at high altitudes are no longer rare. Researchers studying ticks in the Alps found that ticks can survive and reproduce at elevations previously thought unsuitable for their survival.

Because Ixodes ticks transmit Lyme disease and other tick-borne infections—conditions covered in our Lyme disease symptoms guide—the discovery of ticks thriving at higher altitudes raises questions about how climate and habitat changes may influence future disease risk.

Over a four-year period, investigators examined ticks living in the Piedmont region of the Alps and evaluated both the pathogens they carry and the altitudinal limits of Ixodes ricinus. This species is similar to Ixodes scapularis, the blacklegged tick responsible for transmitting Lyme disease in the United States.

A total of 6,492 I. ricinus ticks were collected from vegetation. Questing ticks were also collected from 373 carcasses of red deer, roe deer, and chamois between 2017 and 2019. (A chamois is a species of goat-antelope.)

Many of the ticks found on large animals were presumed to have detached during transport because the carcasses were not placed in plastic bags before examination.

According to the investigators, the number of ticks “was significantly associated with altitude, habitat type, and signs of animal presence, roe deer in particular.”

Although tick numbers decreased with increasing altitude, Ixodes ricinus ticks were found living at elevations as high as 1,884 meters above sea level.

Ticks collected included all three life stages—larva, nymph, and adult. The Centers for Disease Control and Prevention (CDC) considers a tick population established when all three life stages are present in a region.

Ticks Expanding Into Higher Altitudes

These findings were notable because such altitudes and habitats have traditionally been considered unsuitable for I. ricinus survival and development due to colder temperatures, limited secondary vegetation, and drier soils.

Using molecular analysis, investigators identified a broad range of tick-borne pathogens including Borrelia burgdorferi sensu lato, Rickettsia helvetica, and Anaplasma phagocytophilum. Although the prevalence was low, researchers detected Borrelia miyamotoi for the first time in this region.

The authors suggest that climate change may be contributing to the expansion of ticks into mountainous regions.

Fewer ticks were found in coniferous forests and open areas. However, public safety remains a concern because open areas often include picnic sites, walking paths, and other locations frequently visited by hikers and tourists.

Although relatively few cases of Lyme disease have been reported in the Piedmont region, the authors caution that human infections may be underdiagnosed or underreported.

Understanding where ticks live and how their geographic range changes may help guide strategies for preventing Lyme disease.

Why This Matters

As environmental conditions shift, the geographic range of ticks—and the diseases they carry—may expand into areas previously considered low risk.

Ticks thriving at higher altitudes suggest that Lyme disease risk may extend beyond traditional geographic boundaries.

Clinicians and patients alike should remain aware that exposure risk is evolving.

Clinical Perspective

This study highlights an important shift in how we think about tick exposure.

Higher elevations may no longer provide the protection once assumed. As tick habitats expand, clinicians should consider tick-borne illnesses even in patients who report exposure outside traditional endemic areas.

Awareness of changing risk patterns may improve early recognition and prevention of Lyme disease.

Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

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