Whether it’s curing existing diseases or encountering new ones, a bit or a lot of pathologies doesn’t hurt a story or make for a bad plot device. Injecting fear and dread into any scenario can be as easy as prescribing an epidemiologist or two.
The scope in speculating future disease can again be endless, e.g microbial, fungal, genetic, psychiatric, crystalline extraterrestrial agents, or cyber infections
Space-whirly, Plague Ship by Andre Norton
Denver Madness, The Sheep Look Up by John Brunner
The Green Line of Death, The Andromeda Strain by Michael Crichton
Helico virus & Silent Untreated Disease Syndrome, Brian Aldiss’s Helliconia Trilogy
Vampiris pandemic, I Am Legend by Richard Matheson
Zombie plague, World War Z: An Oral History of the Zombie War by Max Brooks.
Snow Crash, Snow Crash by Neal Stephenson
See also Plagues in Science Fiction and Fantasy