The impact of climate change on vector-borne infectious diseases is currently 
controversial. In Europe the primary arthropod vectors of zoonotic diseases are 
ticks, which transmit Borrelia burgdorferi sensu lato (the agent of Lyme 
disease), tick-borne encephalitis virus and louping ill virus between humans, 
livestock and wildlife. Ixodes ricinus ticks and reported tick-borne disease 
cases are currently increasing in the UK. Theories for this include climate 
change and increasing host abundance. This study aimed to test how I. ricinus 
tick abundance might be influenced by climate change in Scotland by using 
altitudinal gradients as a proxy, while also taking into account the effects of 
hosts, vegetation and weather effects. It was predicted that tick abundance 
would be higher at lower altitudes (i.e. warmer climates) and increase with host 
abundance. Surveys were conducted on nine hills in Scotland, all of open 
moorland habitat. Tick abundance was positively associated with deer abundance, 
but even after taking this into account, there was a strong negative association 
of ticks with altitude. This was probably a real climate effect, with 
temperature (and humidity, i.e. saturation deficit) most likely playing an 
important role. It could be inferred that ticks may become more abundant at 
higher altitudes in response to climate warming. This has potential implications 
for pathogen prevalence such as louping ill virus if tick numbers increase at 
elevations where competent transmission hosts (red grouse Lagopus lagopus 
scoticus and mountain hares Lepus timidus) occur in higher numbers.