Viral Invasion

Space age with somewhat reliable gravity systems and basic plasma weapons and nanotechnology, pre-FTL/XT however.

But that is about to change, the first XT is an unusual alien invasion with a biotech probe(s) a transport ship encounters the city sized floating piece of biotech, the biotech is full of smaller biotech that work like viruses on a plantary level to replace the DNA of a planet with that of another. it is unknow if this is an attempt to while out the Terran bionome, a blind terraforming attempt, or a invasion from inside.

Once inside a host the command nodes disperse viruses to restructure the creature into a hybrid to patrol and expand the area. when deployed it appears like a combination insect hive/biotech forrest with biotech crystals everywhere.

Human nanotech can not fully stop the virus, it can however slow it's progress enough for the surgical removal of the command nodes, which leaves the infected person or animal in a semi-hybrid state (and usually either neuter or female) unless they can get a transfusion of human DNA to the nanobots in the system but the reversal process is much slower, this also depends on how fast the infection is slowed those in stage 1 make a complete recovery in stage two transfusion are needed as the human DNA is compromised and in stage three there is little to no hope at this time. Military Medical Nanobots might have better luck but aside from their military grade status there is less of it to go around.