"There is always potential for a conflict of interest between microbe and host because the genetic makeup of the microbe differs from that of the host. Natural selection will favor microbes that act in their own genetic interest as circumstances permit." --evolutionary biologist Paul Ewald, PhD.
As circumstances permit.
Right now in America, circumstances permit the COVID-19 virus to act very aggressively in its own interest. New infections are increasing at a rate where even the logarithmic graph is scarily steep. As I write, nearly 150,000 have died of this disease and soon four million will have been infected, with disturbingly variable effects on their bodies. COVID-19 is a calamity on the scale of a world war, and we haven't even sent our children back to school in the fall yet.
What can we do?
Dr. Ewald has explored in depth the relationship between the characteristics of pathogens and their virulence. He's also researched how host behavior modifies pathogens--something that happens with surprising speed, due to the rapid generation times and high mutation rates of bacteria and viruses.
This interview is an excellent introduction to this way of thinking about human disease:
https://www.pbs.org/wgbh/evolution/library/01/6/text_pop/l_016_06.html
Here's the heart of it, in an answer Dr. Ewald gives towards the end:
"We can summarize this information in a nutshell by focusing on how dependent disease organisms are on the mobility of the host for transmission. If a disease organism is very dependent on healthy hosts moving around [and] contacting susceptible hosts, then we expect natural selection to favor extreme mildness in those disease organisms. If, however, the disease organism is not dependent on host mobility -- for example, if the disease organism is transmitted by mosquito, or contaminated water, or because it's durable in the external environment -- then we expect that natural selection will favor high levels of harmfulness in those disease organisms."
This is, in fact, what we find in the study of infectious diseases. And mosquitos, ticks, contaminated water or food--these are called vectors. External factors that spread disease.
What, then, about America's severe difficulties with the COVID-19 pandemic?
My current thinking is, that careless and maskless people are acting as human or cultural vectors, just as a mosquito acts as an insect vector in malaria, or as water acts as an environmental vector in cholera. And these countless human cultural vectors in America are not only causing more new infections. It's worse than that.
Human cultural vectors are also actually selecting for more virulent, dangerous, damaging strains of the COVID-19 virus. This is because the virus can "afford" to immobilize, severely harm and even kill its human hosts under these conditions of reckless human behavior. Even when COVID immobilizes and kills, it still spreads widely during the incubation period, before the patient becomes ill enough to be immobilized.
With specific regard to schools of all types, if, this fall, students are placed indoors in close proximity with no changes in protocols from how life was before the pandemic, the COVID-19 virus will likely exploit this sudden change in its target hosts' behavior. Currently, it's rare that COVID-19 causes severe harm or death in young hosts. But if effortless viral transmission routes are set up amongst millions of young people in school settings, there's a possibility that random mutations that really harm the young will out-compete the present forms of the virus' RNA in those populations. COVID-19 may depend upon human mobility to spread--but its incubation period is long enough that it can infect others for days before host immobilization due to illness occurs. And there's that pesky variability as well--asymptomatic or lightly symptomatic carriers who remain mobile can infect even more of their peers than those who are taken severely ill.
Is there a way out of all this?
It is likely (almost certain) that if we make it more difficult, through our human behaviors, for the COVID virus to spread, then those milder mutations that do not severely harm and immobilize their human host will out-compete those mutations that debilitate and kill. Because the virus cannot, under those more challenging conditions (from its point of view), “afford” to kill its host.
We would then tame the COVID-19 virus. Dr. Ewald often uses the phrase "domesticate the virus."
The well-known human behaviors that can tame COVID-19 include wearing masks, washing hands frequently and before touching one's face, "respiratory etiquette," social distancing, and surface disinfection. Less talked about but vitally important human behaviors involve proper airflow management in buildings, changing HVAC systems into active virus-killing machines, radical improvements in food handling, managing aerosols created by everything from dental treatment to sneezes to flushing toilets, and probably hundreds more strategies that our culture hasn't even begun to think about or implement yet.
With our backs to the wall now, I'm starting to believe that taming COVID-19 through intelligent and effective human behavior is our only option. A vaccine against any coronavirus species just doesn't seem likely due to the mutation rate and the decrease in levels of antibodies to them over time. Herd immunity is a fantasy—in naturally acquired COVID-19 infections, antibodies and B-cell mediated immunity appear to fade in months, just as they do with all other coronavirus species. Treatments will improve, but one does not "cure" an endemic virus that numbers in the trillions (quadrillions?) planetwide and keeps changing its RNA coding with every passing hour.
COVID-19 appears likely to be a part of our environment permanently, going forward.
And I believe our only viable strategy to defeat COVID-19 is to domesticate it, through intelligent and effective human behavior.
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