Experts Fear Brucellosis Progress Could Slip

Aug 20, 2021  | 7 min  | Ep4701

Out West, the rise of an old livestock disease in wild animals has natural resource officials keeping a close watch in order to be ready for what might come next.

Colleen Bradford Krantz explains in this week’s Cover Story.


The near eradication of brucellosis, a costly bacterial disease that affected a large number of U.S. cattle herds in the early part of the last century, is one of the nation’s major livestock- and public-health triumphs.

Ryan Clarke, Veterinary Services, USDA: “It was very prevalent in 1934, when our brucellosis program began, when they figure maybe 50 percent of the herds were infected. The program began and they started testing for and removing those animals that were infected. By 1957, they reckoned about 13 percent of the herds were infected in the United States, like 234,000 herds. Then in the early ‘40s, they did develop the vaccine… In 2008, for the first time, there were no infected herds in the United States.”

Experts worry, however, that infected wildlife – particularly elk and bison in the Yellowstone National Park area - are slowly reversing some of that progress in cattle. The disease can cause cows to abort their calves and have milk production fall dramatically.

There is additional concern another strain of brucella bacteria that particularly affects hogs is being spread by wild boar in the southern United States.

Ryan Clarke, Veterinary Services, USDA: “Now, since 2008, of course, we’ve had a number of herds that have been infected, but they were infected by wildlife…. Back in the ‘30s, it was people buying cattle that were infected and those cattle infected their cattle. Now, that’s all gone. …but now it’s …wildlife coming into farms and ranches and aborting and passing the disease that way.”

Dr. Clarke, one of USDA Veterinary Services’ top experts on brucellosis, says livestock will sniff or lick the aborted materials and easily become infected with the resilient bacteria.

Brucella, the bacteria that causes the disease, also can be passed to humans - often through unpasteurized milk – and causes fevers and other symptoms that, left untreated, can become chronic.

With Brucella, which cost the livestock industry about $400 million annually in the mid-1900s, now nearly eliminated from U.S. pastures and feedlots, human infections have also fallen.

Ryan Clarke, Veterinary Services, USDA: “They’ve proven in a number of countries that if you can control it in animals, it’s controlled in humans also.”

Because the vaccine currently used on cattle and bison isn’t as effective on wildlife like elk, scientists are working on a new version. There’s one problem: several types of brucella bacteria are included on the federal government’s list of possible biological terrorism agents. As a result, the bacteria falls under strict regulatory controls limiting study to the nation’s most secure scientific laboratories, like the National Animal Disease Center in Ames, Iowa.

Steven Olsen, National Animal Disease Center, Ames, Iowa: “So that meant… bio-level 3, containment for both laboratory and animal work and that’s expensive and most places do not have that capability so, for that reason, you saw the number of laboratories and scientists working in the large-animal hosts go down.”

Recently, some USDA officials have agreed with animal scientists it may be time to consider removing the disease from that list so researchers can work outside the lab. At a minimum, they hope research will be allowed near Yellowstone.

Steven Olsen, National Animal Disease Center, Ames, Iowa: “It’s still kind of a work in progress as I understand it...The agent is already running loose in those wildlife populations out there so you aren’t introducing anything into that environment that’s not already there.”

Dr. Olsen points out that, even with an effective vaccine for wildlife, finding a way to administer it to free-ranging animals such as elk would be problematic.

In Montana, state veterinarian Dr. Marty Zaluski, who has seen area cattle producers have to deal with the return of the disease, has been encouraging federal officials to move ahead with a policy change. If approved, two types of brucella bacteria could be removed from the select agents list. National security officials, however, are still weighing the pros and cons.

Dr. Marty Zaluski, Montana State Veterinarian: “There’s a fairly long history of nations wanting to weaponize brucellosis and use it as a bioterrorist weapon. I believe that certainly the USSR - the prior Russia - had a program. I believe this country looked at it as well ....I believe that historical record is really the reason why this agent was included in this list….But I would argue it’s misplaced.”

Zaluski says treatment and prevention of the disease has come a long way.

Dr. Marty Zaluski, Montana State Veterinarian: “If you are terrorist and you choose your weapon of choice as brucella abortus, you are not the brightest crayon in the box. We have a ready test for this disease, the incubation period - the time from exposure until illness - can be several weeks. We have a very inexpensive and effective treatment for this disease. Contrast this type of an agent to ebolla or anthrax... and it just doesn’t make sense to me.”

Zaluski worries that federal officials could, in trying to protect human health by keeping brucella on the list, inadvertently increase human cases by not allowing the scientific community a simpler way to study brucellosis in wildlife.

Dr. Marty Zaluski, Montana State Veterinarian: “My concern is that without interventions that are effective, brucellosis is going to spread throughout the entire contiguous range of elk in the Rockies and the Northwest. Based on a map I saw from the Rocky Mountain Elk Foundation, that includes anywhere from 10 to 12 states. And so I don’t know whether that’s going to happen in 20 years, 30 or 40 years, but ….the outcome… if we don’t develop better tools, is somewhat bleak.”

For Market to Market, by Colleen Bradford Krantz,

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