We're back again with another episode on climate change and human health.

The effects of a warming planet on our wellbeing are multi-faceted, and there's a lot to address in these complex interactions. One of those things is an increase in disease.

And that's the topic of this week's Healthcare Triage. INTRO MUSIC Recent decades have witnessed an increase in vector-borne diseases like Malaria, Dengue, Lyme Disease, and West Nile Virus. Without climate action, this increase is expected to continue over the next century.

Vector-borne and zoonotic diseases are caused by pathogens carried by insects and/or animals. Things like fleas, ticks, mosquitoes are called vectors. Lyme Disease is a good example with the vector that carries it being a tick., the vector for West Nile Virus is a mosquito, and so on.

The ways and the levels at which these diseases are distributed across time and space are highly affected by climate, which can affect how pathogens evolve, how insects and animals access and interact with humans, and when and where in the world they appear. Take Lyme Disease again as an example. Changes in temperature, rainfall, and humidity that accompany climate change could expand the geographical area in which ticks are found because it makes more areas hospitable to them.

It also increases the amount of time that ticks are out and about and hunting for a tasty snack because higher temps are coming earlier in the year and staying longer. Overall, more available habitat, better breeding conditions, and more hosts may translate to a larger host population. For example higher temperatures in southern Canada have contributed to the establishment of ticks that are vectors for Lyme Disease.

Milder winters in northern Canada are associated with an increased population of the white-footed mouse, which is, you guessed it, a major host of the Lyme Disease pathogen. According to data tick habitats are predicted to expand across a huge portion of the eastern half of the United States by 2080. As temperatures increase, northward expansion of habitats will contribute to this spread.

The annual number of cases of West Nile Virus Neuroinvasive Disease, the most severe form of West Nile Virus, are projected to double by 2050 in the United States alone, partly due to warmer temps. This is projected to result in up to 3,300 additional deaths per year, accompanied by over 3 Billion dollars in hospitalization costs. Beyond increasing spread via this increase in geographical range, climate change can also increase the survival of the pathogens that cause disease by increasing both the survival and reproduction of the vectors that carry them.

Increases in temperature and rainfall can shorten the time it takes for mosquito larvae to develop and can increase breeding sites for vectors like mosquitos. And this isn't just a potential scenario. Our changing climate has already increased the ability of mosquitos to transmit the Dengue virus by 3 to 5.9 percent depending on the mosquito species.

It's worth mentioning that some diseases may actually decrease with global warming because the vectors won't be able to stand the increased heat. According to one publication, about 16 percent of infectious diseases were diminished at some point in response to climate. Well that may seem like good news, I think we all hope there are better ways to decrease disease than heating the Earth to a degree that many organisms can't survive.

And anyway, a lot more diseases are increased than are decreased. According to that same publication, around 58 percent of infectious diseases faced by humans have been aggravated at some point by climate changes. In addition, the authors reported over 1,000 unique pathways by which pathogenic diseases resulted from climate hazards via different routes of transmission.

And it's not just the insects. Animals in the Amazon Forest carry a large number of known, and likely many unknown, pathogens that are a growing concern for human health as deforestation in that region continues. And of course, that deforestation plays a big role in climate change.

Deforestation of tropical rainforests can lead to an increase in infectious diseases by disturbing the natural environment of pathogens and their host by increasing the presence of disease vectors in both forest and urban areas, and again by changing temperature and rainfall such that pathogens are better able to survive, reproduce, and infect humans. Deforestation and other factors like urbanization change the natural environment in ways that increase contact between humans and wildlife which means increased contact with the pathogens that are carried by that wildlife. This can result in what is called "spillover" which is when a pathogen jumps from one species to another.

Spillover is dependant on a lot of different factors, but increased contact between humans and wildlife hosts is a big one. After all, it doesn't matter if a pathogen can adapt to humans if humans never actually encounter it. And this brings us to the point that changes in climate lead to changes in human behaviour that affect disease transmission as well.

Extreme weather events, shifts in seasons, can lead to climate migration, with a shift in population from rural to urban areas. This introduces a lot of concerns when it comes to infectious disease. It can introduce diseases to parts of the world where they weren't previously found.

It increases the number of people in already higher-populated areas, and it makes all of us more connected and reachable in terms of travel patterns. In addition, longer spells of warmer weather can translate to more time spent outdoors for humans, which means more opportunities for unfortunate encounters with these disease vectors. Taken together, these things increase the introduction and transmissibility of infectious disease, potentially to the point of more and worse pandemics.

So this is not all good news. Having just experienced a global pandemic, it is probably feeling especially like not good news. But there are a few things we can try in order to change course, some of which we already know are effective.

Ensuring that low- and middle-income countries have the tools they need to deal with climate change fallout will help to decrease the prevalence of climate migration. Regulating deforestation, particularly in places like the Amazon, is a critical need. Fortunately, policies to do just that have been enacted before and we know they're effective.

And another important move will be making sure urbanization is a more controlled process with thoughtful planning and regulations that keep climate action at the forefront. The good news is that actions like these are becoming more common as climate change becomes a larger part of the global discussion. We have time and we have people who are working hard to understand how we can best use that time to create better climate outcomes.

It feels hard sometimes but let's keep the faith. [end credits music begins] Hey, did ya enjoy this episode? Ya might enjoy this previous episode on climate change and the air we breathe. We'd appreciate it if you'd like this video, subscribe to the channel down below, and consider going to https://patreon.com/healthcaretriage where you can help support the show.

Make it bigger and better! We'd especially like to thank our research associates: Joe Sevits and Edward Liljeholm, and of course our Surgeon Admiral: Sam.