When first colonized from Ian in the late 100's, Raiga
thin tainted atmosphere. Volcanoes were broken open to raise the
density and bacteria were sown to remove the taint from the air.
an unforeseen burst of radiation from Raiga's primary caused
some of the
bacteria to mutate into a deadly strain. While the original taint
been removed, the mutated bacteria proved fatal to most human
inhabitants. A few managed to develop an immunity to the bacteria
"immunes" have multiplied to become a sizeable population, but the
is quarantined to non-natives. Nor can the natives leave, since
carriers of the deadly bacteria Lucellia Raigae.