Red Dwarf S7 E 7 Epideme

The crew encounters an abandoned ship, the Leviathan, which is buried in the middle of an ice planetoid. In it, they find the frozen body of Caroline Carmen, one of Lister's former crushes. She is taken on board the Starbug, where the crew attempts to thaw her out, but they are unable to melt the ice. That night, Carmen defrosts of her own accord and turns out to be in an advanced state of decomposition. She attacks Lister and spits part of her jaw and tongue down his throat, infecting him with Epideme, an intelligent virus (with an annoying personality) that was supposed to cure nicotine addiction, but in practice kills its victims within 48 hours, then reanimates their corpse to find a new victim to transfer itself to.

Lister tries reasoning with Epideme directly through a communication link, but has no luck in convincing the virus to leave. Kochanski comes up with a drastic plan to save Lister's life: coax the virus to move down toward Lister's hand and then cut off the hand, isolating the virus outside his body. However, they end up cutting off Lister's right arm instead of the left one as he had requested, and they only manage to dispose of part of the Epideme virus, with the result that they only succeed in prolonging Lister's life by an hour. Lister sneaks aboard the Leviathan with some explosives, intending to kill both himself and Epideme, but the virus talks him out of it by revealing that the destination of the Leviathan was Delta VII, a research base that might have a cure.

When Starbug arrives at Delta VII, it turns out that the planet has been destroyed in order to deal with a massive Epideme outbreak – a fact that the virus was fully aware of, and used in its attempt to prevent Lister from killing himself. With Lister on the verge of death, Kochanski injects Lister with a drug that stops his heart, then gets his corpse to bite her left hand, infecting it. After amputating her left arm she reveals that it was actually Caroline Carmen's arm, and that her own left arm is intact. Kryten and Kochanski then revive the now virus-free but now one-armed Lister.