Movellan virus

The Movellan virus was developed by the Movellans to attack Dalek casings and tissue.

Its effects were immediate and devastating. Symptoms included loss of motor control, and expiation of whitish foamy substance from vents and seals in the Dalek casing. The infrastructure of the Dalek Empire was harmed so badly by the virus, that the empire broke into factions and fled to distant parts of the universe to avoid infection and find a cure.

Davros was rescued by a Supreme Dalek to develop a cure. Davros instead attempted to use the virus to destroy the Daleks loyal to the Supreme Dalek, and subsequently develop Daleks completely loyal to him. However, Davros' Kaled tissue proved vulnerable to the virus, and he began to display symptoms before escaping captivity.

(DW: Resurrection of the Daleks)