Hair loss syndrome in black-tailed deer was first described in western Washington in 1995. The condition is caused by a heavy infestation of Eurasian louse in the genus Damalinia (Cervicola) sp. The normal hosts of this louse are European and Asian deer and antelope, which are not seriously affected by the lice. In contrast, when black-tailed deer become infested, they develop a hyper sensitivity reaction. This species of lice has been found on elk in Washington, but the elk do not suffer the severe hair loss seen in deer.
Beginning in 2003, WDFW began receiving reports of deer in the Yakima area with symptoms of hair loss syndrome. The lice involved in that infestation were identified as Bovicola tibialis, yet another exotic old world species with fallow deer as the normal host.
For more information on hair loss syndrome, see WDFW's deer hair loss syndrome fact sheet at http://wdfw.wa.gov/conservation/health/hair_loss/.
3rd of February, 2016