Pretenders & Miasma diseases

[Twan]

Some questions about the miasma effect on pretenders...

How are calculated the chances to become diseased in a miasma dominion ?
Are some pretenders immune to the miasma effect or in general to diseases even if they are not cold blooded nor undead ? (according to the text all other creatures seem subject to the miasma diseases, but I find strange that specialized pretenders like the plague lord, very thematic pretenders for Ct'is -father/mother of serpents-, or creatures with swamp survival and/or PR like a green dragon or a wyrm may be affected).
Also according to the description, lifeless creatures have immunity to "drain life, sleep and polymorph" but... nothing about diseases. I think they are immune anyway, but is it confirmed ?