Wiki had some other neat comments too...
"It is possible that the tales of jackalopes were inspired by sightings of rabbits infected with the Shope papilloma virus, which causes the growth of horn- and antler-like tumors in various places on the rabbit's head and body.[1] [2] However, the concept of an animal hybrid occurs in many cultures, for example as the griffin and the chimera. Indeed, the term 'chimera' has become the categorical term for such composites within the English language."
I wonder if this is the same virus that got into Bryan's Setosa? Oh No!