A genetic pathogen is an artificial biological agent used by the Kobali to transform the deceased of other species into more of their kind. The pathogen alters DNA into Kobali protein structures.
In 2376, after Lyndsay Ballard's return to USS Voyager, The Doctor identified the genetic pathogen that had changed her into Jhet'leya but informed her that there was no longer enough of her former genome to reverse the process. He designed an inaprovaline compound that would make her cosmetically Human, but in time the pathogen began to counteract this as well. (VOY: "Ashes to Ashes")