Imperium Nihilus: Vigilus Defiant (2018), p34 — Legacy of Plague

Calgar demanded the matter of Dontoria be addressed as a higher priority than the Ork assaults and Genestealer Cult uprisings. The Ultramarines had been critical in the war against Mortarion and his Death Guard, and he knew well that to allow the faithful of Nurgle a foothold was to see unnatural disease spread rapidly soon after. Ultimately, the barrier between reality and the warp would thin to the point that the spawn of Chaos could manifest in realspace. That nightmare could not be allowed to be made real.