Papilloma virus may explain the "jackalope" legend

The photo is one of three images of a diseased rabbit, explained at Reddit as suffering from a viral infection:

The cottontail rabbit papilloma virus (CRPV), or Shope papilloma virus, is a type I virus under the Baltimore scheme, possessing a nonsegmented dsDNA genome. It infects rabbits, causing keratinous carcinomas, typically on or near the animal’s head. These tumors can become large enough that they interfere with the host’s ability to eat, eventually causing starvation.

The Wikipedia entry adds:

The virus is also a possible source of myths about the jackalope, a rabbit with the antlers
of an antelope, and related cryptids such as the wolpertinger. Stories and illustrations of horned rabbits appear in scientific treatises dating back many years, such as the Tableau encyclopédique et méthodique, from 1789 [image at right]