Ticked Off: Climate Change and the Spread of Infectious Disease

I was discussing the diagnosis with a friend. The raised, red bull's eye led to only one conclusion: he had to have Lyme disease. Our only hesitation was that it was early March, surprisingly early for ticks.

The conversation sparked a question: is Lyme disease spreading because of global warming? A little research turned up a few reports that confirmed our fear: climate change is, in fact, spreading the geography of Lyme. Confirmation can be a poor solace when it comes to disease.

For those of us who grew up in New England, where the woods remain dark and damp through the summer, each trek into the woods warranted a check for the small deer ticks known to carry Lyme. Though the disease has been reported in 49 of 50 states, nearly 99% of those cases are limited to the 5 geographic areas of New England, Mid-Atlantic, East-North Central, South Atlantic, and West North-Central. Ask a doctor from Darien about the disease, and they'll provide a lecture; ask a doctor from Denver, and they'll demur. Lyme has, and remains, very much a Northeast disease.

That is changing. Climate change has set the stage for the spread of Lyme across the North American continent, and abroad. Consider a few examples.

Ticks, mice are the primary hosts of Lyme, with birds playing a small role. According to predictions, climate change will alter rainfall patterns, while increasing areas of floodwater and humidity in the atmosphere. Together, these point to the kind of warmer, damper conditions in which disease-carrying pests like ticks, mosquitoes and rats, can thrive.

The other dominant factor is the increase in average global temperatures. The northward spread of warming conditions means the northward spread of infectious-diseases like Lyme into higher latitudes, while the increase in minimum temperatures similarly means the extension of these diseases into higher altitudes. Milder winters and higher average temperatures mean that regions of Canada and North American mountain ranges that have been too cold to host disease vectors are becoming increasingly suitable to the transmission of disease. According to one study, Lyme could move 200 kilometres north by 2020 and 1,000 kilometres north by the 2080.

There's no question that climate change is altering the epidemiology of infectious disease. (Click here for a study on the healthy risks associoated with climate instability.) But in the case of Lyme, our concern should be tempered not only by an understanding that the disease's geographic proliferation comes slowly, but by a reminder that it is spreading north into Canada and south into the Southern United States -- both regions of relative affluence with a strong public health education and medical resources.

Other areas of the world, namely the poorest regions -- areas of Africa, India and China -- will face compounding problems. The effects of climate change -- depletion of water, drought, and erosion -- could overcome already minimal public health resources and undermine struggling agricultural activity. The densely populated, low-lying mega-deltas in Africa and Asia will be especially hard-hit by coastal flooding, erosion, and wet-land loss.

Together, these changes threaten millions of people with an increase across the spectrum of the most basic human-health related troubles: increased malnutrition, increased death, disease and injury, and increased burden of diarrheal disease. This means the world's poorest children will be further handicapped by developmental disorders.

For those of us living in North America, climate change makes clear the true degree of our affluence. For every degree of suffering we sustain, we can be certain the world's poor are suffering more.

At this point, climate change is no longer a scientific question. It's a moral question, as well. Because when it comes to climate change - a problem of global cause and consequence - the responsibility, and the suffering, is spread unevenly.

Perhaps as Lyme and other infectious diseases spread north, it will remind us to spread our wealth south and east in the form of aid to those who need it most.