What causes Hair Loss Syndrome (HLS) in Black-tailed deer? This syndrome is caused by a heavy infestation of the Eurasian louse.
In the spring, black-tailed deer show signs of hair loss syndrome (HLS) which is caused by a heavy infestation of the Eurasian louse. Normally affecting the European and Asian deer, the black-tailed deer have become infested and tend to develop a hypersensitivity reaction to the lice. This causes yellow or white patches along their sides. The lice cause an irritation of the skin and excessive grooming by the deer leads to loss of the guard hairs.
Deer become heavily infested during winter and early spring and many die during this time, especially fawns. Deer that do survive will re-grow their hair and gain weight again during the summer.
Another study concluded that Deer Hair Loss Syndrome (DHLS) is called a syndrome, not a disease, because the cause and method of transmission are not completely understood. The syndrome is most common in black-tailed and Columbian white-tailed deer. Common symptoms include yellow or white appearing hair or bare patches of skin. At first, some deer have darkening or almost black patches of fur. Later, deer may appear emaciated and lethargic, and exhibit excessive loss of hair.
These deer often have a heavy infestation of muscle worms that contribute to their sickness. Poor immune function also may be a contributing factor (Oregon Department of Fish and Wildlife).
Normally moulting of hair of a healthy deer happens twice per year in the spring and late summer. The distribution of hair loss is usually patchy and the deer tends to look scruffy until the moult is complete. A normal moult can be distinguished from disease conditions of the skin by the presence of a normal appearing coat beneath the moulting hair.
Captive deer have been treated with medication for DHLS but there is not practical method of treating deer in the wild.
There are no known cases of humans, pets or livestock contracting DHLS from affected deer.