Their most telling improvement involved a fundamental parameter: population size of the hosts.
Viruses face four basic challenges: how to get from one host to another, how to penetrate a cell within that host, how to commandeer the cell’s equipment and resources for producing multiple copies of itself, and how to get back out – out of the cell, out of the host, on to the next. A.
The purpose of this book is not to make you more worried. The purpose of this book is to make you more smart.
From this perspective, the most serious outbreak on the planet earth is that of the species Homo sapiens.
So you have density, infectivity, mortality, and recovery – four factors interrelated as fundamentally as heat, tinder, spark, and fuel. Brought together in the critical measure of each, the critical balance, they produce fire: epidemic.
Another implication was that epidemics don’t end because all the susceptible individuals are either dead or recovered. They end because susceptible individuals are no longer sufficiently dense within the population.
I think the virus is present all the time, within reservoir species,” he told me. “And sometimes there is transmission from reservoir species to other species.
The result will be gradual transmutation of heritable forms, and adaptation to circumstances, by a process of selective culling. Eventually he gave the crank a name: natural selection. Twenty years passed after the E notebook entry. The world heard nothing about natural selection.
If you look at the world from the point of view of a hungry virus,” the historian William H. McNeill has noted, “or even a bacterium – we offer a magnificent feeding ground with all our billions of human bodies, where, in the very recent past, there were only half as many people. In some 25 or 27 years, we have doubled in number. A marvelous target for any organism that can adapt itself to invading us.
If SARS had conformed to the perverse pattern of presymptomatic infectivity, its 2003 emergence wouldn’t be a case history in good luck and effective outbreak response. It would be a much darker story.
Will the Next Big One come out of a rainforest or a market in southern China?
In other words, HIV hasn’t happened to humanity just once. It has happened at least a dozen times – a dozen that we know of, and probably many more times in earlier history.
Any tiny little thing that people do,” Dwyer said, if it makes them different from one another, from the idealized standard of herd behavior, “is going to reduce infection rates.
We should appreciate that these recent outbreaks of new zoonotic diseases, as well as the recurrence and spread of old ones, are part of a larger pattern, and that humanity is responsible for generating that pattern. We should recognize that they reflect things that we’re doing, not just things that are happening to us. We should understand that, although some of the human-caused factors may seem virtually inexorable, others are within our control.
From the ecological point of view an outbreak can be defined as an explosive increase in the abundance of a particular species that occurs over a relatively short period of time.” Then, in the same bland tone, he noted: “From this perspective, the most serious outbreak on the planet earth is that of the species Homo sapiens.
At the Chatou market in Guangzhou, for instance, he had seen storks, seagulls, herons, cranes, deer, alligators, crocodiles, wild pigs, raccoon dogs, flying squirrels, many snakes and turtles, many frogs, as well as domestic dogs and cats, all on sale as food.
You could also buy leopard cat, Chinese muntjac, Siberian weasel, Eurasian badger, Chinese bamboo rat, butterfly lizard, and Chinese toad, plus a long list of other reptiles, amphibians, and mammals, including two kinds of fruit bat. Quite an epicure’s menu. And of course birds: cattle egrets, spoonbills, cormorants, magpies, a vast selection of ducks and geese and pheasants and doves, plovers, crakes, rails, moorhens, coots, sandpipers, jays, several flavors of crow.
Human-caused ecological pressures and disruptions are bringing animal pathogens ever more into contact with human populations, while human technology and behavior are spreading those pathogens ever more widely and quickly. There are three elements to the situation.
Vast areas of old forest have been cut, or chained down with bulldozers, to make way for cattle ranching and urban sprawl. People have planted orchards, established urban parks, landscaped their yards with blossoming trees, and created other unintended enticements amid the cities and suburbs. ‘So bats have decided that, as their native habitat is disappearing, as climate is becoming more variable, and their food source is becoming less diverse, it’s easier to live in an urban area.
History is a fable agreed upon.
Once a species of insect or bird has reached a new island and established a population, evolution toward gigantism does offer certain advantages: fat storage, thermal stability, and defense against predators, if there are any. But gigantism is also a way of becoming flightless, and flightlessness is a way of becoming marooned.