Ticks Thrive at High Altitudes in the Alps

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, 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.

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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 tick-borne infections.

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

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