From Creatures Wikia
Norn Immunidefiency Disease is an illness in Creatures 2 that is only found in certain Norns made with a Genetics Editor. NIV is similar to HIV; it weakens the Norn's immune system, making it vulnerable to dangerous diseases that could be fatal, such as AIDS. Norns also infected with NIV will pass it on when they kiss-pop, which can lead to an epidemic. However, regular Norns are completely uneffected by NIV, as they do not have the genes required to become infected.
The NIV Norns and NIV were created by Mike L Anderson