Fever Plague
A rare and deadly disease with no known cure until recently. This disease fatally infected both Jonathon and Martha Kent in Superman's youth and left him an orphan despite his efforts to help them. Years later, the same disease infected both Lois Lane and Lana Lang, but Superman, after much difficulty, was able to cure them.
Superman's parents were infected with the disease while on vacation in the Caribeean when they discovered and opened Pegleg Morgan's chest on vacation. In doing so, they inadvertantly exposed themselves to the disease as they released it. They quickly succumbed to the illness despite Clark's desperate attempts to save them.(S No. 161, May 1963: "The Last Days of Ma and Pa Kent")
Much later in 1981, an accident with an artificate at a museum in Metropolis leads to Lois Lane and Lana Lang as well as Clark Kent being infected. While Clark's super immunity quickly subdues the infection, he is well aware that his loves would have only hours to live.
To save them, he tries enlisting Lex Luthor's aid to find a cure. Although Luthor was confident he could do it, he bluntly refuses Superman's offer to reduce his prison sentence in return for a cure. Furthermore, the criminal scientist taunts the superhero by trying to infect himself with the disease. Superman stops the attempt and Luthor mocks him cruelly about his stubborn adherance to his principles even for his most dangerous enemy despite the stakes involved.
Superman decides to cast the women into the Phantom Zone to keep them alive until a cure can be found, but the Phantom Zone prisoners damage the projector severely enough that repairs would take days longer than the women have.
Accepting the inevitable, Superman gives the women each a wonderful night out with Lana as Clark and with Lois as Superman. Then he takes them to the Fortress of Solitude as their infections reach the final stage.
Superman then is inspired to go to the future to see if a cure could be found. However upon arrival, the future Terrans refuse to give it as it would dangerously pollute the timestream. Fortunately while returning to the present, Superman realizes that because he was infected by the disease himself. That means his own blood's antibodies that destroyed his infection could be used to help the women. Superman puts the idea to the test with a double infusion of his blood into them and cures them. In the future, the Terrans noted that was when the cure for the fever plague was found and while it might have been better to tell Superman that, they ultimately decided "All's well that ends well. (S No. 363, September 1981: "The Dying Day of Lois and Lana!")
