No Biochemical Barriers: Difference between revisions

** The Goa'uld are a race of parasitic worms that evolved on some distant planet, but seem to be capable of infecting every sentient race they come into contact with, without any discernible difficulty. They supposedly need to acquire the genetic code from a species they're going to infest and apparently do this via sex, which is...[[Nightmare Fuel|odd]], at least the first time. Also, the Jaffa were initially created to allow larval Goa'uld time to adjust to human hosts. (Prior to the Jaffa, many more Goa'uld died of rejection sickness.) The Goa'uld still can't parasitize some species, such as the Retou. It's also explicitly noted a couple times that some species or human populations are resistant or immune to Goa'uld infestation, but the Goa'uld make a habit of wiping them out.

* A ''[[Doctor Who]]'' episode had a human stung by the venomous tongue of a Silurian warrior, and begin to mutate. This trope is simultaneously played straight (it does affect him), subverted (the Silurian doesn't understand why he doesn't just die) and partially justified (Silurians and humans are both technically earthlings; they are just separated by millions of years of evolution).

* ''[[Star Trek: Enterprise]]'' had an episode where a disease that was apparently a universal infector was used as a sociology experiment by an alien race that had surpassed physical existence -- they wanted to see what cultures would do if infected by an incurable airborne alien virus that killed quickly.

** The Star Trek novel ''Uhura's Song'' was all ''about'' finding the cure for an epidemic striking both humans and the catlike Eeiauoans, complicated (among other factors) by the fact that nobody on the planet that should hold the solution recognized its symptoms.