A rare and deadly disease long without a cure. This disease fatally infects both Jonathan and Martha Kent in Superman's youth and leaves him an orphan despite his efforts to help them. Years later, the same disease infects both Lois Lane and Lana Lang, but Superman, after much difficulty, is able to cure them.
Clark Kent's parents are infected with the disease while on vacation in the Caribbean when they discover and open the treasure chest of 18th century pirate Pegleg Morgan. In doing so, they inadvertently expose themselves to the disease within the chest. They quickly succumb to the illness despite Clark's desperate attempts to save them (S No. 161/1, May 1963: "The Last Days of Ma and Pa Kent").
Much later, in 1981, an accident with an artifact at a museum in Metropolis infects Lois Lane, Lana Lang, and even Clark Kent. While Clark's super immunity quickly subdues the infection, he is well aware that Lana and Lois have only hours to live.
To save them, he tries enlisting Lex Luthor's aid to find a cure. Although Luthor is confident in his ability, he bluntly refuses, even after Superman offers 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, who personally cannot take the chance that Luthor couldn't create a cure for himself, stops the attempt and Luthor mocks him cruelly about his stubborn adherence to his principles and how they even apply to himself, a master villain.
Superman decides to cast Lana and Lois into the Phantom Zone to keep them alive until a cure can be found, but the Phantom Zone Criminals damage the projector severely enough that repairs would take longer than the women have to live.
Accepting the inevitable, Superman gives each women a wonderful night out--he sees Lana as Clark and Lois as Superman. He then takes them to the Fortress of Solitude as their infections reach the final stage.
Superman is inspired to go to the future to see if a cure can be found. However upon arrival, the future Terrans refuse to reveal 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, his own blood's antibodies will destroy the infection and can be used to help the women. Superman puts the idea to the test with a double infusion of his blood and cures them. In the future, the Terrans note that this is how the cure for the fever plague was meant to be discovered and while it may have been better to tell Superman, history would lead to the proper outcome (S No. 363, Sep 1981: "The Dying Day of Lois and Lana!").