The plague has no descriptive title and no other name. It simply is called the plague, and has been since its appearance in the early days of the Coalition. The very word is enough to strike fear into the hearts of the living, be. it makes no distinction between race, sex, class, or species. Nothing is safe from it, save the Zaian, and even they fear its coming.
What is it?
This terrible affliction is a fungus-like organism; highly adaptable and very infectious. It is nigh impossible to kill, without exterminating everything else around it. Unlike more natural diseases, the plague has a very long "silent" period where it shows no symptoms, and goes infectious shortly before displaying those symptoms. The plague will infect anything remotely sapient that it can touch; as long as it is organic, it will find a way to infect it. It does not infect lesser creatures, like beasts of burden or wild animals, or plants and algae. When plague expends itself on a planet, every trace of it is removed within a few decades.
Symptoms and Stages
All this information is the compilation of accounts left behind by victims, and in some cases, the ongoing observations of brave souls infected but still reporting to securely isolated listeners, either in orbit or in closed-system facilities.
The first signs of infection is an extended period of insomnia, followed quickly by odd behavior and trouble with advanced motor functions that the ignorant would ascribe to sleep deprivation. Coughing and wheezing sets in as the fungus spreads throughout the body. By this point, the spores are already beginning to leave, others are infected too. The infected gets more clumsy over a period of days, and begins losing minutes and even whole hours of his life. He does things not of his own volition without realizing it, as he loses control of himself. Little does the unwitting victim know it, but this is the plague testing control of his nervous system, which it seized in the incubation period.
Not long after come the first visible signs, sparking panic and alarm in the population around them. Where one infected is, others will follow. Small white stalks, almost too small to even see, start to emerge from the skin, growing bigger as time goes on. Once through the skin, the fungus begins to spread over the outside of the body as it fills and smothers the inside. Soon, the plague-stalks grow within the eyes. Many choose to die before this occurs, but the unfortunate linger on in an ever more unfeeling stupor, blinded and listless. The inside of the mouth and throat is coated in the plague-matter, every breath breathed spews out hundreds of thousands, if not millions of spores, into the air.
By this point, none can say if the infected person is still themselves, or if some other creature now controls the wretched body. The stalks continue to emerge, and eventually, the plague strangles the body to death. From the corpse grow the fungus-like matter, linking up with other plague-matter nearby, forming vast mats of fuzzy white mass for a time.
It is only a few weeks before this abomination starves to death, having expended its energy on growing in mats for seemingly no reason, but the spores remain active for up to ten years. Sometimes ships emerge from the ether, both the crews, passengers, and plague dead, but with spores very much alive, ready to be unleashed upon the living. More suspicious Tarsin Chroniclers have commented that such incidents are no accident, as two great waves of plague have begun with empty ships. It has become standard Coalition policy to board drifting ships with full exosuits donned, and to be doused with gamma rays after investigation. But most plague (and diseases in general) spreads through interstellar travelers, which is why the Coalition is very strict with populace wishing to travel from system to system.
See also: Sickness in Space
The only short-term solution to a plague infection is neutron bombing; a dark mercy for the populace. When a race cannot do this themselves, the Zaian have made it policy to intervene, and do it for them, regardless if it was requested or not. There are many so-called dead planets in the galaxy, where the Imperial Navy or Zaian have bombarded the cities and towns from orbit until nothing but ghostly ruins stood testament.
For hardier races, and weaker-bodied ones who do not fear cancer, gamma ray treatment is a viable cure if one suspects they've been infected. Given that bathing the nervous system in gamma radiation is usually not a good idea, this is usually only a solution for those who really need to live another few years at most. Emperor Vektôs the Sailor used gamma treatment to survive the plague to buy himself enough time to have a son born to him.
Strangely enough, the plague has been observed fighting and disabling nannites. This is the heftiest piece of evidence for those in the camp who believe it to be an artificially-created weapon that escaped into the World at large. The fact that it leaves planets with their populations dead but infrastructure and ecosystem untouched adds credence to this theory. But the questions of who might have made it, when, why, and how remain unanswered.
[insert Age of Plagues history episode here]
The Earthmen of Sôl are fortunate not to have encountered it in their initial forays into the World. If the Earthmen had blundered upon dormant spores in their early explorations, it is possible they would not be among the races of the World today.