Avian flu! Swine flu! Now, bat flu?
Last week I sent you a news article on the recent coronavirus, first described in Wuhan, China, that was emerging as a 'new' human virus, one not previously detected in humans or known to cause human disease. A week later, as you know, this remains the top health news story, and rightly so - the virus has now killed many dozens, and infected many thousands, around the globe.
Viruses are a bit of an evolutionary quandary. They are tiny objects, composed of protein and nucleic acid. They are not considered to be cells, and they are not considered to be 'alive'. They are parasitic 'replicating devices' - they can only replicate when they have successfully infected the cell of a host species. And, they are designed to take-over the protein machinery of their host's cell, causing it to make many more virus particles, and to spread them.
Mammals have evolved with viruses throughout our history, and our immune systems contain some viral defenses, just as our genomes contain bits and pieces of DNA that may have been viral in origin. In recent years and decades, we have increasingly been aware of 'new' viruses, not previously seen in humans, that are suddenly causing human disease. Swine flu, avian flu, MERS, SARS, and others - and now, the Wuhan coronavirus.
Why are viruses so common in mammals? Because we are really good hosts for them - lots of cellular protein machinery, warm-blooded cells which promote high rates of viral replication, dense social structure which promotes transmission. From rats to cats, bats, camels and more, each mammalian group bears its own viral load.
Why do viruses move between mammal species? Two words: mutation and opportunity. As viruses mutate, they can gain or lose features that make them better, or worse, suited for particular host species (e.g., cats versus dogs). As species co-mingle, the odds improve that a virus can successfully 'make the leap' to a host of a different species, one to which it is newly well-suited.
Why are so many of these novel viruses originating in Asia? Population density and food production practices. On the global scale, the U.S. is relatively sparsely populated (save our largest cities). Across the globe, it is very common for population densities to be much higher than those found here. And, high human densities require ramped-up food production. Much of food production here is commercialized and removed from the public, but again, this is a global exception. Across most of the world, food production tends to be on a smaller scale, and it tends to be much more personal - individuals tending their own animals, working with their tissues and bringing their own products to open market. Together, this density and close contact ups the risk of transmission of animal viruses to human hosts.
What can we do? Addressing the inequities of education and opportunity that put some more at risk of public health diseases than others is a global problem, one that is daunting in scale. Can we immediately correct it? No, of course not. We can, however, be careful consumers, paying attention to the kinds of products we purchase, their degree of commercialization, the level of exploitation that may be attached to them. We can pay attention to climate issues, which seem to exacerbate many emerging diseases. And personally, we can practice good public health ourselves - stay up-to-date with vaccinations, follow good hand hygiene protocols, cover our coughs and our sneezes. And, we can stay informed, and help others to be informed - that is perhaps the best defense of all.
I hope that, by this time next week, the spread of this coronavirus has been contained.