Deer have a new enemy: Epizootic Hemorrhagic Disease.

The virus has already killed more than half of the 300 blacktailed deer in UCSB’s Sedgwick Reserve. The deer at the 6,000-acre natural research center developed high fevers, brain hemorrhaging, blindness, deafness and erratic behavior before dying. The virus, however, only seems to infect deer, which is good news for the reserve’s California condors and human caretakers.

The two-month-old outbreak initially appeared to affect only deer at Sedgwick Reserve, though deer carcasses have been recovered from the Woodstock and Rancho Siswoq Areas in the foothills of the Santa Ynez Mountains. When the deaths began two months ago, a number of potential causes besides a virus were put forward, including humans poisoning the deer. Scientists have now narrowed their suspect list to mosquitoes or ticks wielding Epizootic Hemorrhagic Disease.

“Two weeks ago, we took our first good blood sample; the deer had a temperature of 106 degrees, which is some of the highest recorded for ungulates,” Sedgwick Reserve Director Michael Williams said. “It had lost all abilities of hearing and sight.”

The deer was discovered just before it died, feeble and unable to struggle or run – a lucky find for biologists. Animals tend to hide any signs of injury or illness because predators read any sign of weakness as an invitation to dinner. The deer’s condition made the sample especially useful because it meant the blood was more likely to contain the lethal virus.

Diane McClure, the campus veterinarian, said the deer’s blood sample was tested for “virus isolation.” The blood was sent to UC Davis, and schools as far away as Iowa and Michigan, for testing. Blood cultures determined that the virus killing the deer is likely Epizootic Hemorrhagic Disease.

“If it’s that disease, which they’re almost certain now, it only affects deer,” Williams said.

Identifying the disease is an important step in containing it. Deer are still dying, but one hope is that disease will burn itself out by spring.

“The virus is an orbivirus, moved around by biting insects,” said Samuel Sweet, associate professor of ecology, evolution and marine biology. “This sort of thing pops up occasionally, then suddenly disappears.” It results in “increased pressure in brain and spinal fluids, which leads them to suffer a whole series of strokes. The pressure is not pleasant.”

If mosquitoes are infecting the deer, the plague could end by winter, Sweet said.

“Because of the first few frosts, the mosquito transmission cycle is probably gone because they can’t withstand the cold,” he said.

On the other hand, if weather-resistant ticks are transmitting the Epizootic Hemorrhagic Disease, the virus could last an indeterminable amount of time.