Sandworms of Dune - Entry #3

     Biological warfare was a successful tactic for Omnius 15,000 years ago and it is only logical that Erasmus would have spend part of the time fine tuning a virus that was more effective at eradicating humankind than the one used during the Butlerian Jihad.  One of Murbella's advisors understands the thinking machine's strategy:

Accadia struggled to sit up in the chair.  "Mother Commander, don't be so focused on the epidemic that you fail to see its consequences."  She began coughing.  Blotches had appeared all over her skin, the advanced stages of the disease.  "This plague is a mere foray, a test attack.  On many planets it is sufficient, but the Enemy must know the Sisterhood well enough by now to be sure we can fight this, at least to a point.  After they soften us up, they'll attack by other means."

(Sandworms of Dune, p. 205)