Spillover: the powerful, prescient book that predicted the Covid-19 coronavirus pandemic.

by David Quammen

she began talking about susceptible individuals, infected individuals, and recovered individuals in a given bat population. If the population is isolated and insufficiently large, then the virus will move through it, infecting the susceptibles and leaving them recovered (and immune to reinfection), until there are virtually no susceptibles left. Then it will die out, just as measles dies out in an isolated human village. Eventually the virus will return, brought back to that population by a wayward, infected bat. This represents the same blinking-Christmas-light pattern that I invoked with regard to Marburg. The ecologists call it a metapopulation: a population of populations. The virus avoids extinction by infecting one relatively isolated population of bats after another. It dies out here, it arrives and infects there; it may not be permanently present in any one population but it’s always somewhere. The lights blink off/on in their turns, never all lit, never all dark. If the bat populations are separated by distances great enough that those distances are seldom crossed, then the rate of reinfection is slow. The lights blink off and on languidly. Now imagine one such bat population within the metapopulation. It has progressed through the SIR sequence, every individual infected, every one recovered, and the virus is gone. But not gone forever. As years pass, as the birth of new bats and the death of old ones raise back the proportion of susceptibles, the population regai...

Metapopulations and the Christmas light analogy of pathogenic propagation