Alien- Necromorph Desc

As they watched, barnacle-like pustules and raised black lesions erupted on the larva’s body. Gagnon recognized the symptoms at once—cellular necrosis, with which they had infected Hassan the last time he’d visited the lab.
“The creature appears to have drawn from the genetic material of its host,” Brigette said.
“Yes, and although Hassan was treated for the cellular necrosis, traces of it lingered in his body. The larva must have contracted the condition.” Cursing inwardly, Gagnon felt like a fool. It had never occurred to him that the host’s genetic make-up might play such an integral role in Xenomorph development.
Obviously it did, though, and now the larva had contracted one of the deadliest diseases humans had ever encountered.
...

At first, he thought it had died, for it had gone completely still. An instant later it rose up, like a cobra preparing to strike, and then it slithered the rest of the way free from Hassan’s ravaged chest. As they watched, the infant Xenomorph slithered along Hassan’s stomach, down his legs, and then it slipped over the side of the bed and flopped onto the floor with a wet smack. It began moving swiftly across the floor, leaving a trail of blood in its wake.
Fear turned to euphoria.
Somehow, Gagnon surmised, the larva had adapted to the disease it had inherited. The creature hadn’t healed entirely—the pustules were still there, and the lesions—but it had managed to integrate the necrosis into its own genetic make-up without dying. He had never imagined that such a thing might be possible.

Prototype, Chapter 9