SANTA FE – With the sudden deaths last week of more than 100 elk in an area of less than a square mile – and no other unusual deaths or sickness noticed since – New Mexico wildlife biologists are facing a confounding mystery that likely will take weeks to solve.
“I’ve never seen anything like this,” said Kerry Mower, wildlife health specialist with the state Department of Game and Fish.
“And I’ve talked with other wildlife biologists who’ve seen large die-offs, and I’ve not run across anyone who has seen anything of this magnitude,” he added in a telephone interview Wednesday. The deaths were reported the morning of Aug. 27 on private land between Las Vegas and Ocate.
Various materials have been sent to laboratories both in and out of the state for testing, but it will take weeks to get results, Mower said.
But one immediate public health threat has been ruled out: anthrax, which occurs naturally in New Mexico.
“That was ruled out right away,” said Paul Ettestad, public health veterinarian with the state Department of Health.
That still leaves a lot of other possibilities, but no obvious front-runners. One of the most unusual aspects of this case is that so many animals were affected so quickly in such a short period of time – perhaps a day or so.
Mower said he has some regrets that the department’s news release and subsequent media reports on the die-off pointed a finger toward epizootic hemorrhagic disease (EHD). Some aspects of the event are consistent with such a diagnosis, but others aren’t, he said.
For example, deaths from an infectious disease generally are spread out over a longer time as creatures are infected and get sick on different days as it spreads among a herd.
And, Mower added, it does appear that a whole herd may have been affected by this die-off. The dead animals included mostly females and calves or yearlings, with a few young males who hadn’t gone off on their own yet. “If there are any survivors, they are not milling around the area,” he added.
Also, while EHD is relatively common in New Mexico, resident animals don’t often die from it. That’s because they usually are exposed to it often enough to have a reservoir of antibodies to fight off an infection, Mower said. In other words, they are immune.
Animals that do die from EHD in New Mexico generally tend to be, for example, elk brought in from other states to a game ranch. If those imported animals don’t have antibodies to EHD, they may die after being exposed here to the virus, which is carried by gnats, he said.
“In New Mexico, Arizona and western Texas, the exposure (of animals to EHD) is often enough that we don’t see mortality,” Mower said.
When a lot of animals die in a short period of time in a small area – in this case, think of an area three-quarters of a mile long and one-third of a mile wide, Mower said – the suspect generally is a single point source. “Something they all drank or ate,” Ettestad said.
Mower said he four-wheeled all around the site and didn’t see any obvious groupings of poisonous plants. But, he added, some subtle changes sometimes can make a plant deadly. Under certain soil conditions, for example, plants might pull up excess selenium, a trace element that in high enough doses can fell an animal as large as an elk, he said.
“If you Google ‘elk die-off,’ you get 2004 in Wyoming, where many died very close to each other,” Ettestad said. It turned out that they had eaten a certain type of lichen off rocks that, in a post-drought situation, had become toxic, he said.
The New Mexico carcasses have been left in place, Mower said. “In this kind of heat, they go really, really fast,” he said, adding that ravens, vultures, coyotes and bears all have been feeding on them. There has been no sign of those other species becoming ill or dying, which potentially could happen if the dead animal had ingested a toxic substance.
But not necessarily. “There are some toxins that are less deadly to carnivores than to ruminants,” Ettestad said.
So, at this point, the mystery remains while everyone awaits test results on everything from gnats caught in the area to the stomach contents of the dead elk.
“I’d rather not even speculate on what caused it,” Mower said.