Can vaccines replace the hunt?

In a 1997 study the National Academies of Science concluded that, short of a wholesale slaughter of elk and bison in the greater Yellowstone area, the only way to control the disease was to vaccinate all of the park’s bison and elk. Two brucellosis vaccines have been developed for cattle, and one is being tested for use in bison. But the results to date have not been promising, according to Tom Roffe, chief of wildlife health for the U.S. Fish and Wildlife Service. “[The vaccine] confers some immunity in cattle, but it is not great,” he said, noting that cattle in Wyoming that had been vaccinated still contracted brucellosis in 2003. “We know [the vaccine]’s not highly effective in bison.”

Furthermore, Roffe said, tracking and vaccinating 4,900 wild bison is not like giving shots to animals in pens. Given the low level of protection the vaccination affords, he said, it is not worth the expense to vaccinate the park’s herds until a better vaccine is available. Steven Olsen, a researcher at the USDA’s Animal Research Service, said promising work is underway. “There are new vaccine strains, and new technologies have been developed to make more strains,” Olsen said. “Completing the research is not simple. It is going to be years.”

In the meantime the state of Montana has started a plan to create a brucellosis-free bison herd. State rangers have captured 14 Yellowstone bison and plan to capture and quarantine 200 more. The animals go through repeated tests, a process that takes months, to determine whether they are brucellosis-free. The herd will then be bred and relocated in the wild, but not in Yellowstone, where they would again be exposed to brucellosis. The brucellosis-free bison will remain free-ranging outside the park, since they will pose no threat to livestock. Keith Aune, chief of wildlife research at the Montana Department of Fish, Wildlife and Parks, said the project is already under attack from some quarters. “There is opposition to anything you do with bison,” Aune said. “The agriculturalists fear we might be helping spread brucellosis. The environmentalists say the project is cruel to the animals. I look at it as one way to preserve the species.”

Some biologists, including Roffe, believe elk pose a much greater threat to livestock than bison. Recent outbreaks of brucellosis in Idaho and Wyoming have been traced to elk that had mingled with cattle herds. Terry Kreeger, director of veterinary services at Wyoming’s Department of Fish and Game, said there is a lot of debate over how to handle elk in Wyoming, where the animals are kept at feeding grounds during winter. “The elk who feed at the feeding grounds have a rate of infection that is ten times higher than those that do not come to the feeding grounds,” Kreeger said, noting that concentrating the animals increases the spread of brucellosis.

“But we can’t just do away with the feeding grounds, because people don’t want to see elk starving in winter either. Also the feeding grounds can actually help to direct the elk away from cattle.” There are no vaccines that work on elk, and elk have been known to pass the disease to cattle in Wyoming.

Now the state is planning to slaughter female elk that test positive for brucellosis at one of its feeding grounds this winter as part of a test program. But Wyoming doesn’t expect its elk-kill to grab headlines or draw protesters the way Montana’s bison hunt has. “The bison are icons, because they are in Yellowstone,” said Aasheim of Montana’s wildlife department. “But until there’s a solution, we are going to use hunting as a tool to manage them.”

National Geographic
December 6, 2005

Original web page at National Geographic