Coronavirus: What if...?

In order for models to be useful, it is only necessary that they provide reasonably accurate predictions; it is not essential that they detail the exact mechanisms that underlie the things that they represent. It is very common for people to use anthropomorphic explanations for phenomena that do not involve characteristics or capabilities of humans, for example when we say say that an electron "sees" an electric field, or that nature "abhors" a vacuum. It is sufficient that that ascribed characteristics permit an inference as to how the system being modeled will behave.

Likewise, fiction writers can ascribe any manner of fantastic or even impossible mechanisms in order to make their stories work. This is essential to science fiction and ghost stories, and to any manner of heroic epics. The mechanisms themselves do not have to be reasonable or real, they just have to make the story work.

We may take a similar approach in contemplating the coronavirus. One of the most striking facts about our developing experience with the virus is the wildly varying effects that it has on different places and different populations, and the seemingly contradictory and inexplicable observations that arise from that experience. We note, for example the rather severe course of contagion in New York, and Italy, and compare these with rather mild experiences in Poland or Oregon. We are struck by the marked difference in mortality between Italy and Germany. We note the oscillating pattern contained in the daily new case charts from various places. We might ask ourselves, if we were novelists, trying to craft a story that contained these phenomena, what mechanism would we choose? Alternatively if we were to try and derive a model, with the priority of making appropriate predictions, what sorts of behavior would we assume for the virus and the populations and environments in which it circulates?

We might start by ascribing strategies, both to the virus and to the human population that it affects. We need not create a cognitive, planning agent. that manages such strategies, but simply accept that the behavior of the virus and its interactions with humans proceeds as though there were such an agent. One mechanism that we might contemplate, for example if we were writing fiction about the virus is epigenetics; the idea that organisms change as a result of differences in gene expression rather than in the genetic code itself. We have two possibilities here: that the organism subject to epigenetic phenomena is the human population subject to infection, or the virus that does the infecting. We might also consider that it could be both.

This gives us a starting point, either for a story or of a model that epigenetics represents a mechanism by which organisms appear to pursue strategies that optimize some outcome of benefit to the organism. For example, it may appear that the strategy of contagion of the virus requires that not all infected people die. Therefore the virus may behave as though there were some feedback that affects expression of viral genes that slows spread when large numbers of people are infected all at once. This may explain (certainly not the only explanation, and by no means an exclusive or even correct one) the appearance of the rhythmic peak-and-trough pattern observed in the documented experience of widely separated countries and states. It is possible to at least conceive that there is an epigentic phenomenon by which pathogens are regulated so as not to kill off the entire population of hosts subject to infection.

Another possibility is that there is an epigenetic phenomenon in people, such that innate immune responses, for example limit disease spread in patient who are not infected and therefore have no specific immunity to the disease. This may explain the experience of the Diamond Princess in which only about a fifth of the passengers were infected while on board, but some became infected after disembarking. It may also explain why some places like California and in particular homeless populations are not awash in dead bodies, even though the size of the antibody positive population seems rather modest. One of the interesting observations made by Daniel DeFoe in his journalistic-fiction work A Journal of the Plague Year is that the severity of disease in those infected declined as the contagion waned. Even though the book itself was fiction (DeFoe was only 6 at the time of the Great Plague) it was based on journals and recollections of family members, and therefore may reflect an actual phenomenon. If so, it would be consistent with an epigenitic basis for contagion and virulence.

This same phenomenon (again a literary device or modeling convenience, not necessarily a biological fact) would explain the wide variety of disease severity, the appearance of asymptomatic carriers and most significantly, the low absolute prevalence of coronavirus infection. The same approach can be used to account for the widely divergent rates of mortality observed for the virus. It may be assumed that the concept of "strategy" as mentioned above is merely an anthropomorphic device that provides a point of reference for why things may behave as they do. It implies no conscience and surely no empathy or sentimentality. We note that when bird flu emerged, the rational response was to slaughter millions of chickens. Killing off the host significantly impedes spread of the virus. It may be reasonable to consider an epigentic strategy in human populations as well: kill off those most likely to spread the infection to others, without commensurate detriment to reproduction or survival of the larger group. Furthermore, we can contemplate an environmental influence on these mechanisms. Italy has a higher mortality than Germany, and New York has a higher mortality than Oregon because they are different environments. They people in them may not seem outwardly different, but the way in which individual physiology interacts with the environment is different.

An obvious objection to even considering an epigentic, or other mechanism that requires some manner of organism level communication, effect is that it defies explanation. It seems fantastic to consider that virions may alter genetic expression, or that the immune response of unifected humans can depend on the infection status of those around them. There are however precedents for observing changes in population dynamics and disease transmission that seem to reflect a strategic element hard-wired into biology. It is useful to think of the virus, the human population, and the environment as components of a system, and a system which contains complex feedbacks and dynamics. Complex systems operate about points of equilibrium, and these points are determined by the dynamics. One interesting article that touches on the point is helpfully titled Ecological Feedbacks Can Reduce Population Efficacy of Wildlife Fertility Control. This is an article by Ransom, Powers, et al., in the February 2014 issue of the Journal of Applied Ecology. It contains the observation that "Disease transmission was 28% higher in populations of possums Trichosurus vulpecula with sterile females, illustrating the potential for decreased survival in fertility-controlled populations." The interesting thing about this statement is that is suggests that there is some feedback by which the presence of sterile females in an animal population affects transmission of disease; it suggests that there is some mechanism by which the fertility of some female members of a population feeds back, i,e, is communicated to other members of the population and affects disease transmission.

This is not to argue for an epigenetic mechanism driving or controlling a pandemic. It is merely a speculation that illustrates that if we want to explain the variety of observations and data, conflicting and varied experiences, the relatively benign and severe experiences in places where one would expect similarity, etc., our understanding of what affects the spread of the virus and the nature of the disease that it causes must necessarily be much more advanced than it currently is.