Germ Warfare M*A*S*H : Season 1 Episode 11

Hawkeye moves a wounded North Korean soldier into The Swamp, rather than let him be shipped out before he's stable. During the night he and Trapper play Dracula, and siphon off a pint of Frank's blood. The soldier then contracts hepatitis, so they have to test Frank without him knowing, and have to keep him away from Margaret and the patients.