Doctor Who (1963)

S15E5 The Invisible Enemy (1)

In the year 5000 AD, a supply shuttle from Earth encounters a mysterious, sentient virus in deep space. This virus rapidly infects the crew at a refueling station on Titan. The situation becomes critical when the Doctor also becomes infected. Meanwhile, Leela remains inexplicably immune. As the team races against time, they must uncover the virus's true intentions and why Leela is unaffected.