Colorado Parks and Wildlife officials have identified the cause as shope papillomavirus, a rabbit-only virus with no cure that produces wart-like tumours known as papillomas, particularly around the face and head of cottontail rabbits, 9NEWS reports.

Some rabbits in Colorado are sporting unusual wart- and tentacle-like growths, but officials say it's not something to worry about.

They may look like real-life jackalopes, but these rabbits owe their peculiar appearance to an infection caused by a cousin of the human papillomavirus.