Viruses, 'Nature's immune response to the human parasite'

Reproduced below is the epilogue from The Hot Zone by Richard Preston. It's still relevant today with the emergence of SARS, H1N1 and the novel coronavirus (2019):

The emergence of AIDS, Ebola, and any number of other rainforest agents appears to be a natural consequence of the ruin of tropical biosphere.

The emerging viruses are surfacing from ecologically damaged parts of the earth. Many of them come from tattered edges of tropical rain forest, or they come from tropical savanna that is being settled rapidly by people. The tropical rain forests are the deep reservoirs of life on the planet, containing most of the world's plant and animal species. The rain forests are also its largest reservoirs of viruses, since all living things carry viruses. When viruses come out of an ecosystem, they tend to spread in waves through the human population, like echoes from the dying biosphere.

Here are the names of some emerging viruses:

Lassa. Rift Valley. Oropouche. Rocio. q. Guanarito. VEE. Monkeypox. Dengue. Chikungunya. The hantaviruses. Machupo. Junin. The rabieslike strains Mokola and Duvenhage. LeDantec. The Kyasnur Forst brain virus. HIV, which is very much an emerging virus, because its penetration of the human species is increasing rapidly, with no end in sight. The Semlike Forst agent. Grimean-Congo. Sinbis. O'nyongnyong. Nameless Sao Paulo. Marbury. Ebola Sudan. Ebola Zaire. Ebola Reston. [And SARS. MERS. H1NI. Coronavirus.]

In a sense, the earth is mounting an immune response against the human species. It is beginning to react to the human parasite, the flooding infection of people, the dead spots of concrete all over the planet, the cancerous rot-outs in Europe, Japan and the United States, thick with replicating primates, the colonies enlarging and spreading and threatening to shock the biosphere with mass extinctions. 

Perhaps the biosphere does not "like" the idea of five billion humans. Or it could also be said that the extreme amplification of the human race, which has occurred only in the past hundred years or so, has suddenly produced a very large quantity of meat, which is sitting everywhere in the biosphere and may not be able to defend itself against a life form that might want to consume it. Nature has interesting ways of balancing itself. The rain forest has its own defenses. The earth's immune system, so to speak, has recognized the presence of the human species and is starting to kick in.

The earth is attempting to rid itself of an infection by the human parasite. Perhaps AIDS is the first step in a natural process of clearance. 

AIDS is arguably the most serious environmental disaster of the twentieth century. The AIDS virus may well have jumped into the human race from African primates, from monkeys and anthropoid apes. For example, HIV-2 (one of the two major strains of HIV) may be a mutant virus that jumped into us from an African monkey known as the sooty mangabey, perhaps when monkey hunters or trappers touched bloody tissue. HIV-1 (the other strain) may have jumped into us from chimpanzees – perhaps when hunters butchered chimpanzees. A strain of simian AIDS virus was recently isolated from a chimpanzee in Gabon, in West Africa, which is, so far, the closest thing to HIV-1 that anyone has yet found in the animal kingdom.

The AIDS virus was first noticed in 1980 in Los Angeles by a doctor who realized that his gay male patients were dying of an infectious agent. If anyone at the time suggested that this unknown disease in gay men in southern California came from wild chimpanzees in Africa, the medical community would have collectively burst out laughing. No one is laughing now. I find it extremely interesting to consider the idea that the chimpanzee is an endangered rain-forest animal and then to contemplate the idea that a virus that moved from chimps is suddenly not endangered at all. You could say that rain-forest viruses are extremely good at looking after their own interests.

The AIDS virus is a fast mutator; it changes constantly. It is a hypermutant, a shape shifter, spontaneously altering its character as it moves through populations and through individuals. It mutates even in the course of one injection, and a person who dies of HIV is usually infected with multiple strains, which have all arisen spontaneously in the body.

The fact that the virus mutates rapidly means that vaccines for it will be very difficult to develop. In a larger sense, it means that the AIDS virus is a natural survivor of changes in ecosystems. The AIDS virus and other emerging viruses are surviving the wreck of the tropical biosphere because they can mutate faster than any changes taking place in their ecosystems. They must be good at escaping trouble, if some of them have been around for as long as four billion years. I tend to think of rat leaving a ship.

I suspect the AIDS might not be Nature's preeminent display of power. Whether the human race can actually maintain a population of five billion or more without a crash with a hot virus remains an open question.

Unanswered. The answer lies hidden in the labyrinth of tropical ecosystems. AIDS is the revenge of the rain forest. It is only the first act of the revenge.