AIDS

One day, above each major city of the world, rockets were reported to be circling lazily in the sky.  Dilapidated rockets, soaring, leaving wispy trails of vapour in their concentric paths. Their bodies were surreal and shabby against an azure sky normally frequented by airliners.  The media delivered images of their tenuous hulls, made from scraps of flailing metal sheet and rusted plates, orbiting the cities with a disturbing silence.  They were impervious to harm.  Humanity shared a feeling of helplessness.  But there was no harm as the rockets circled tirelessly, and people came to accept this strange new phenomena which they clearly couldn't change.

As suddenly and as unannounced as the rockets had appeared, they one day hurtled ground-ward and exploded, leaving in their place massive tree-like growths with trunks hundreds of metres in width.  The world once again reacted in a panic and struck out at these towering edifices, angrily flogging chunks of moist block and sap from the skin of the alien gargantuans, using chains and vehicles and fire, then bombs and missiles.  But the alien plants were just too thick to be severed, and the roots had established themselves at such unworldly depth and webbed complexity so as to make burrowing them out impossible.  Many people fled the cities in fear.  After a few months, however, the strange growths of plant life had not hurt anyone, and they were accepted as benign.

Then the alien plants started dropping pollen.  Millions of people died, excoriated by bulbous clumps of the corrosive yellow pollen which flayed the flesh and dissolved the lungs of its victims.  Animals died, and cities became desolate of life as evacuations were forced into the countryside.  Governments fled, where they were prepared, into underground caverns.  Many did not. Humanity found itself dispersed into pockets of survivors running constantly from the sick and dying.  The sickness was not contagious, but desperate groups of the uninfected denied sanctuary to the leprotic hordes, and often murdered them.  Countries shrunk to small city states.

AIDS was a cure.  Well, at least it was a treatment - there was no cure to the pollen.  People infected with the AIDS virus had a life expectancy a few months longer than the average infected person, and so AIDS became a commodity illness for those  unfortunate survivors who weren't selected for planetary evacuation or underground sanctuary.  AIDS, which had been rampant in some places of the world, was found only amongst the minority.  The blood of the infected was spilled and sold or traded, bartered and bought, often for admission to the crowded shelters.  Humanity borrowed time from it, and it became the only hope for the dying and the sick for a little longer time to live on a world that ultimately no longer belonged to humans.