Murmuration - S1-E9
Plot hole: The team went to look for a leopard with a natural mutation which would imply a black panther or a leopard with a mutation. But then they find normal leopards who have already started killing people, and in the hospital it was clear that the leopards were already exposed to Reiden's Mother Cell, yet they persisted with the "cure".
Answer: In the episode "Blame It on Leo", Leo Butler, who use to work for Reiden, tells the group about the "mother cell." He explains it's Reiden's molecule vector. So it's something Reiden created. In real life science, vector cells are used to introduce DNA sequences from one organism to another. There are a variety of ways for this to occur, however, in the show not much explanation is given about how Reiden's mother cell works (and tends to bend how it works to the will of the plot).
Bishop73