Star Trek The Original Series Rewatch: "The Pirates of Orion"
Production episode 22020 Stardate: 6334.1 Captain’s log. There’s been an outbreak of choriocytosis on the Enterprise, but McCoy has it under control, so the ship can still fulfill its mission to attend the dedication ceremony for a new Academy of Sciences on Deneb V. However, Spock collapses on the bridge and is taken to sickbay. He’s contracted choriocytosis, and it’s fatal to beings with copper-based blood. The nearest supply of the only drug that can cure him is four days away, but ...
Source: tor.com