And now for something completely different

I got an email a few days back that was totally unrelated to climate change. In college I got on this mailing list that aggregates and distributes reports of outbreaks of diseases of interest. Though I don't do bio anymore, lately I stay on it because the mailing list's editors often include little tidbits of background and explanation about the news blurbs they post, so it's an on-going practical education in which diseases epidemiologists care about (including the less famous ones), how they relate to population behavior, what the differential diagnoses are, how they're controlled, and so on.

This digest had an article about dog displacement in India. Dog displacement refers to capturing feral dogs in an area where they're causing problems (biting people, spreading rabies, etc.) and transporting them some ways away from the population center where, supposedly, they'll be less of a problem (or somebody else's problem).

From the perspective of rabies control, this is a problem in two ways. First, displaced dogs may have rabies, since rabies can take quite a while to show symptoms. So dog displacement can spread rabies around an area much more quickly and uncontrollably than natural churn would. Second, areas cleaned of dogs don't stay that way for long. New dogs move in. These new dogs may have rabies (even if your old population didn't), and because they're new to the area, they'll be more on edge and less familiar with the local people - more prone to fighting and biting. So from a rabies control perspective, it's much better to create a local feral population of dogs that have all been vaccinated against rabies. The article quotes Dr. Lisa Warden, managing director of ABC India: "A stable population of vaccinated dogs is one of the best defenses against rabies in rabies-endemic locations as they keep new, possibly unvaccinated, potentially rabid dogs out of their areas."

This reminded me of Laurie Garrett's The Coming Plague, a book whose text is somewhat less scaremongering than its title would suggest. It's a series of analyses of the emergence and spread of several different diseases, and the basic message is, new disease emerge (and controlled, stable flows of old diseases blow up into epidemics) when some shift in the ecosystem occurs - a population moves or begins to behave differently, and this offers a new niche or transmission mechanism for the disease. You then have epidemics, until the population figures out what's going on and adopt new behaviors that control it.

So back to climate change. The standard line on climate change and disease is that as temperatures rise, tropical diseases will migrate further and further from the equator because their tropical hosts - like the mosquitoes that carry malaria, which could become a disease of the American south.

But what's more interesting to me to think about is how shifts in behavior, migrations of populations, and so on may destabilize ecosystems, resulting in new niches and transmission methods for diseases. What new diseases might emerge as animal populations shift in response to climate? What old diseases will blow up in when they find new niches? How will human behaviors change and what unexpected effects will that have on the opportunities open to microorganisms? When I was chatting about this with a friend who was interested in the same subject, one thing we thought of was this: when it comes to the emissions impact of meat sources, beef is the worst (because cows are ruminants). Chickens and pigs are better. But chickens and pigs living in close proximity to humans provides more opportunity for the passing back and forth of various strains of influenza. If climate change control efforts caused a large-scale shift away from cows toward pigs and chickens as meat sources in the US, would it affect the epidemiology of influenza in the US?