What Is Wrong With That Deer?

Have you ever seen a deer walking around your neighborhood or in the woods that has odd skin “warts” and thought to yourself, “What is wrong with that deer?”  Well, you wouldn’t be the only one.  Even though it's fairly rare, Idaho Fish and Game receives a few calls each year about deer with abnormal skin growths.

These deer may have dark colored, sparsely-haired growths which are likely to be fibropapillomas, also known as fibromas or simply warts.  This skin disease is called "fibromatosis".  White-tailed deer, mule deer, and other ungulates are susceptible to the skin disease.  The virus that causes deer fibromatosis is species-specific to ungulates; therefore it can't be transferred to humans.

Fibropapillomas are usually sparsely-haired, round, appear firm, and may be located anywhere on the deer.  Sometimes deer have just one or there can be numerous fibromas scattered throughout the skin.  They generally are less than 5 inches in diameter and may be dark in color or appear to be bleeding.  

Fibromas are found mostly on younger aged deer and it is thought the disease can be transmitted through direct contact between deer.  However, the mechanics of transmission aren't completely known and contact with an object that has been in contact with a fibroma may also spread the disease.  Another possible transmission path is by biting insects. 

Most of the time deer with fibromas are unaffected unless the growths are located in areas that impede normal activities like eating, walking, or vision.  The disease is not a significant cause of death for deer and fibromas usually disappear over time.  Deer often develop immunity for fibromatosis after having it, so if they are reexposed as an adult they are generally not affected.  A very small percentage of deer have fibromas.  This condition is not new; it's been present in deer for a long time.

Fibromatosis is species-specific and humans are not known to be affected by the disease.  As unsightly as it is on the outside, meat from a deer with fibromas is not affected, as the fibromas are attached to the skin and not in the muscles underneath.