Climatic suitability for tick-borne diseases

In Europe, while several tick species are involved in the transmission of pathogens, Ixodes ricinus stands out as the primary vector. This species is particularly significant for spreading Borrelia burgdorferi, the bacterium responsible for Lyme disease, and the virus causing tick-borne encephalitis (TBE) — two of the most common vector-borne diseases in the northern hemisphere.

Lyme disease, if untreated, it can lead to more serious complications affecting the joints, heart, and nervous system. Tick-borne encephalitis can result in severe neurological disorders, including meningitis and encephalitis.

This indicator uses a threshold-based approach to estimate the number of months with optimal climatic conditions (i.e., temperatures ranging between 10 and 26°C and relative humidity above 45%) for Ixodes ricinus nymph feeding activity, in areas where land cover is suitable for ticks.

Caveats

While suitable climatic conditions play a relevant role, the availability of intermediate hosts, such as rodents, birds, and roe deer, also influences tick populations. Although land suitability indirectly considers host availability, it does not explicitly include their ecological requirements.