The Mystery of the Horned Rabbit: Cottontail Rabbit Papilloma Virus

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    When on a hunt with your rabbit dogs, chances are you may have stumbled across a bizarre creature or two. In truth, this could mean a lot of things, as science has a way of surprising us with mutations and other types of odd appearances. One such example of this is Shope Papilloma Virus, which is sometimes referred to as Cottontail Rabbit Papilloma Virus (CRPV) and causes unusual growths to protrude from the bodies of rabbits.

    If you think back to myths you have heard over the years, one that might come to mind is the jackalope. This animal was a horned rabbit, bearing a rack much like that of a deer. It may be possible that you have seen such a critter in a taxidermy shop. The jackalope itself is not a real animal, but the concept of a horned rabbit actually does hold a kernel of truth; it is possible for rabbits to develop growths on their heads that resemble horns thanks to CRPV.

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    Photo: Ryot

    Research into this unusual condition was performed initially back in the 1930's by a scientist by the name of Richard Shope. Upon hearing tales of horned rabbits, he requested one be sent to him. Experiments conducted on these horns revealed the source to be a virus, and he was able to transmit it to other, healthy rabbits, which then grew horns as well. Further research was then done by Francis Rous, who created a liquid from the virus and injected it into rabbits, which caused aggressive, terminal cancer; the head tumors are often malignant as well, causing squamous cell carcinoma. This then led to research on other types of growths with the ultimate conclusion being the establishment of a link between papilloma viruses and cancer thanks to Harald zur Hausen in the 1970's. It is clear that some strains of papilloma virus have evolved to carry cancer causing potential, but as of now it is not clear why.

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    Photo: Flickr

    CRPV is found in rabbits in the wild as well as pets and it is contagious amongst rabbit species. It is most frequently seen during summer and fall due to the presence of biting insects known as arthropods (ticks, mosquitoes), which aid in the spread of the disease. Lesions are generally seen on the upper portion of the rabbit but sometimes appear on feet as well. They will take a circular shape in most cases and be larger than one centimeter in length. The only definitive way to diagnose this disease is through biopsy of the growths, but the visual aspect is pretty damning.

    Dogs, on the other hand, are affected by a strain of papilloma virus that is referred to as COPV, or Canine Oral Papilloma Virus. While this can affect dogs of all ages, breeds, and either sex, it does not transmit from dog to human, or dog to rabbit. Likewise, dogs are unlikely to catch CPRV from rabbits due to the strain essentially being species specific as well as one being cutaneous and the other mucosal. Humans are generally affected by papilloma viruses that reside in different bodily areas than those on rabbits, so transmission is unliklely in this case as well. While dogs may get growths in and around their mouths, it is not due to rabbit contact. Instead, it comes from another dog and can in turn be spread again to fellow canines. COPV growths will sometimes be beaten by the dog's immune system alone, but in severe cases will have to be removed.

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    Photo: Canine Papilloma Wordpress

    Despite the inability of CPRV to infect humans, the question remains as to what one might do if they find themselves in possession of an affected rabbit. While no link between a rabbit and human has been established regarding the transmission of a papilloma virus, whether or not to eat such an animal is and remains a personal choice as there is no guarantee the virus will not or has not mutated to a new strain that could ultimately be spread. A good choice when it comes to the game you eat is always to be better safe than sorry and avoid consuming a rabbit that appears ill in any way, shape, or form.

    Have you ever encountered a horned rabbit in the field? Do you have plans in place should you come across such a rabbit? Let us know in the comments!

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