How climate change provides a perfect environment for tick-borne Lyme disease
By Eloise Bristow
While many species will struggle with the challenge of a changing climate, the disease-bearing blacklegged tick is not one of them. More temperate conditions characteristic of climate change creates a more favourable environment in which these vectors can flourish, corresponding to the unprecedented increase in Lyme Disease incidence across the US.
The rise of Lyme Disease in the US
While the exact number of cases is nuanced, research suggests ~476,000 Americans are diagnosed with Lyme Disease each year. Although most people who get Lyme disease are cured with antibiotics, around 20% of people will experience a debilitating constellation of symptoms including fatigue, joint and muscle pain, and brain fog. With around half a million people a year contracting Lyme disease, this “post-treatment Lyme syndrome” is a significant source of disability that results in serious emotional, physical and economic harm across the country. A recent study from Carnegie Mellon University found that climate change will cause cases of Lyme disease will increase 21% in the next 30 years.
Optimal conditions for tick survival
The life cycle of the blacklegged tick or, Ixodes scapularis, is highly tuned to their environment. Optimal tick survival and activity happens at temperatures above 45 degrees fahrenheit, with humidity of 85%. Seasonal cold weather brought upon by winter ordinarily activates a hibernation period, during which nymphs lie dormant and molt into adults.
How is climate change causing a rise in Lyme Disease?
The recent success of the blacklegged tick boils down to the following climatic changes:
Generally warmer and more humid weather, makes new niche environments hospitable which previously were not, such as high latitudes. Additionally, humans in these regions are less prepared for ticks during outdoor endeavours.
Rising temperatures accelerating the development, reproduction and lifecycle of blacklegged ticks.
Less extreme seasonal weather changes, allowing ticks to bypass a dormant winter hibernation period, and giving them opportunity to be active on warmer winter days.
Shorter winters allow ticks to thaw and become active earlier in the season.
Increased reservoir host species survival and reproduction, due to less harsh winter conditions means more food is available to the ticks.
More disease transmission opportunities: with fairer weather comes increased ability to make contact with humans.
The effect of climate change upon tick-borne diseases is illustrative of the intrinsic link between our environment and public health. While temperatures will continue to warm, we still have some influence over how much. Staying out of the highest emissions scenarios to preserve temperate climates and cold winters in some regions of the US will mean fewer cases of Lyme disease.
For the environments already hospitable to ticks, local land management practices, such as restoring forests and reducing fragmentation practices are effective in reducing the number of mice, and therefore infected ticks in a region. While this is clear, the prevalence of Lyme disease, and the damage it causes to people's lives calls for immediate adoption of critical prevention measures and ecosystem protection measures.