The Accidental Infection of K'anam Prime
In 2152 C.E.E., a deep space exploration ship manned by a multigenerational Human crew on a rotational hibernation cycle landed on an unknown (to Humans) planet, in order to make first contact with what they identified as an alien species. Unfortunately, the crew of Humans neglected to take thorough precautionary measures to prevent them from accidentally harming the new species. While the science and medical officers did take some precautions by removing any potentially-harmful bacteria from the away team, it wasn't enough. They overlooked the fact that any kind of newly introduced bacteria could be extremely dangerous to the Raxians, even healthy bacteria that aid Humans in their everyday bodily functions.
It is believed that this extreme negligence and error in judgement was caused by the cryogenics used for the crew's rotational hibernation cycle, due to the fact that early cryotech is now widely known to have been bad at preserving brain function. Historians believe this design flaw caused a slow degrading of reasoning skills, impulse control and IQ in the early Human space pilots.
Manifestation
By introducing several new species of bacteria to the Raxian population of K'anam Prime, the crew of Humans managed to spread a plague through 3 continents, resulting in the deaths of hundreds of millions of Raxians.
The plague appeared very similar to the Earth common cold and was, therefore, incurable at the time. This did not stop the Human medical personnel from trying, however, though the job was made doubly as hard due to the fact that they had never seen Raxian physiology before.
Though the majority of K'anam Prime residents were killed during this epidemic, there were a few who developed an immunity to the disease. This prevented the epidemic from wiping out every K'anam resident. Fortunately, those who lived in the Eetera, P'ran and T'vok regions were not on good terms with the K'anam Prime region at the time of the outbreak and, therefore, did not visit their neighbouring region.
Localization
The outbreak was contained within the old K'anam regions of Vaikorix. This left the Eetara, P'ran and T'vok regions of the planet mostly unaffected by the disease which devastated the rest of the planet.
Type
Natural
Ouch. And fairly realistic, I could definitely see this happening.
Necromancy is a Wholesome Science.
Thank you! I'm trying to make this sci-fi world as realistic as is plausible, so I'm glad to hear that it's paid off in this case