Climate change leads to the emergence of exotic diseases

While growing up farming in the tropics, bugs of all kinds were unwanted daily companions. Daily life included a dose of mosquitoes, spiders, scorpions, poisonous grubs, praying mantis and ticks. With all the deadly poisons and diseases that those bugs have to offer, it is a wonder that I lived to tell the tale.

The tropics are warm and humid year 'round. The foliage is always lush and crops grow year 'round, so bugs have plenty to eat and are active year 'round as well. As we move towards the Earth's poles we find less diversity of fauna and flora, as the climate becomes less welcoming. In climates like those we experience in Canada, freezing winters create a barrier that keeps the bugs down.

Or they did.

When I came to Canada twenty years ago, ticks were a rarity. I only found ticks on hikes into the deep woods. Later on I started finding them in the fields around my house in the Bay of Fundy. Today, ticks live in suburban areas and one of them made it to my pillow in my home in Dartmouth.

Decades of burning of fossil fuels have increased the concentration of carbon in the atmosphere. More carbon translates into more heat becoming trapped, and thus a gradual warming of the planet. The effects of a warmer climate are more noticeable as you move north.

The Arctic is already seeing changes. Some of them seem positive: an ice-free Arctic facilitates mineral exploration, melting of ice in the Arctic Ocean opens new and shorter shipping lanes. For the whole of Canada, warmer weather with a longer growing season seems like a desirable change.

But these days everything comes in a bundle: warmer weather means a longer growing season, but it also means more drastic climate events, with higher damage potential. It also comes with some of the pretty bugs and diseases with which I grew up.

Ticks are an example of the negative side of climate change, since more of them can survive through warmer winters. In addition, as cities expand further and further into wildlife habitat, the competition for territory between humans and animals becomes greater, and it becomes more likely that we will end up in the path of diseases usually circulating exclusively among wild animals.

Some field mice carry a bacterium called Borrelia burgdorferi in their blood. Ticks become infected with Borrelia when feeding on those mice. Infected ticks then pass the Borrelia bacterium on to the deer. Borrelia lives a happy life, cycling among the bodies of mice, deer, ticks, and some birds. Up to this point it seems that these animals do not become ill from the exposure, or if they do, we do not notice it.

But ticks do not discriminate among species. If a warm-blooded animal, say a dog or a human, crosses their path, they'll hang on to it. If the tick happens to carry Borrelia and stays on the victim long enough, it will pass Borrelia on to the new host. Here Borrelia exhibits its disease-causing abilities, inducing in the host what is known as Lyme disease.

Thus, the spread of Lyme disease, including its recent appearance and increase in Nova Scotia, is arguably the result of climate change and increasing urban sprawl.

Lyme disease presents initially as an acute illness with flu-like symptoms. At this stage it is treatable with antibiotics. However, there is a chronic form of the disease with long-term debilitating symptoms that morph into many known diseases in humans (e.g. chronic fatigue syndrome, rheumatoid arthritis, mental disease etc.). These diseases also have parallels in animals. In animals we can prevent Lyme disease with chemicals to repel or kill ticks and with vaccines to build immunity against Borrelia. While preventative measures are effective in the short term, over the long term they will be only partially effective. Ticks will acquire resistance to the chemicals and new one will have to be introduced periodically.

We need to take a holistic approach as a community, and address the ecological factors that lead to the spread of ticks, mosquitoes and other bloodsucking creatures native to the warmer climates.

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