The following Open Game Content originates in a 3PP Source
Since rot grubs only feed on living flesh and use dead flesh as an incubator, undead are not harmed by infestations of the parasites. A corporeal, non-skeletal undead infested with rot grubs transfers one rot grub to any creature that touches it or to any creature it strikes with a touch attack or with any natural attack. The target may make a DC 15 Reflex save to avoid being infested, but otherwise is immediately subjected to a single grub burrowing through his flesh. A rot-grub-infested undead’s CR increases by +1.