The rakghouls were deformed mutants living in the Undercity of the Outer Rim world of Taris. They plagued the inhabitants of the Undercity- criminals or their descendants- with their bites having the power to mutate their victim into another rakghoul.
During the occupation and blockading of Taris by the Sith, the Sith troopers assigned to search for crashed escape pods in the Undercity were given a serum that could be used to counteract the effect of a rakghoul bite. Whether this serum ever found its way to the public in the turmoil that followed is of little consequence, as the planet was destroyed a short while after.
It is likely that the rakghouls survived the bombardment, along with the outcasts of the Undercity.