Additional brucellosis cases found in Wyoming herds

In addition to the existing case in Park County, brucellosis has been confirmed in a privately owned bison herd in Park County, and is suspected in a cattle herd in Sublette County.
Preliminary tests Nov. 23 indicate possible brucellosis in one Sublette County cow tested at the Riverton Livestock Auction. By the next day, the Wyoming State Veterinary Lab confirmed a second blood test as “hot.” The suspect herd is under quarantine, and was blood-tested Nov. 28, by Wyoming Livestock Board (WLSB) veterinarian Chris Strang. Adjacent and contact herds are being notified, and the cow has been slaughtered and tissue samples sent for culture testing. Results of the blood and culture tests are expected within the first week of December.
While the infection outbreak in the bison herd is not related to the brucellosis case in the Park County cattle herd discovered in late October, it is within the Wyoming Designated Surveillance Area (DSA), and appears to also be caused by exposure to infected free-ranging elk.  
“The (bison) herd owner was selling 12 heifers by private sale for out of state slaughter,” said Wyoming Assistant State Veterinarian Bob Meyer at a public meeting in Meeteetse Nov. 30. “The herd owner wanted to make sure they were clean from brucellosis, and had them tested Nov. 10. Out of the 12 heifers, there were two reactors. We euthanized one of the heifers and took blood and tissue samples that were cultured by the Wyoming State Veterinary Lab and the National Vet Services Lab. On Nov. 24 that heifer was confirmed to have Brucella abortus, Biovar 1, the field strain of brucellosis.”      
The WLSB’s state veterinarians began testing the herd, and out of 253 bison, 18 more reactors were discovered.     
USDA-APHIS designated the herd as an “affected herd,” and the WLSB quarantined it and one adjacent herd. Meyer anticipates testing to be completed on the affected herd and adjacent herds by Dec. 10. Epidemiologic interviews are underway to determine the extent of this outbreak. The WLSB is referring to the affected bison herd as Herd 2, while the case discovered in the Park County cattle in October is referred to as Herd 1.
Meyer says there are about 1,400 head of bison in the entire herd, and he is working with the owners to test the remainder of the herd and develop a herd management plan.  
“There are two contact herds for sure, and there may be one or two more,” says Meyer.  “No cattle have gotten in with these bison, and the bison haven’t gotten out, but there are cattle that share a boundary. We’ve tested all the cattle herds that were related to first herd, and we have a good start on some of the herds that are adjacent to second herd. Some of the herds that are adjacent to the second herd are also adjacent to the first herd, and they’ve already been tested and were negative. So far, we haven’t found any cows in an adjacent herd that could explain the infection of those herds. The preliminary epidemiology points to infected elk as probably being the source of these infections.”   
Over the past year and a half, USDA-APHIS has coordinated with all state veterinarians to develop changes to the federal brucellosis rules. The state veterinarians of Wyoming, Idaho and Montana have had considerable input into these discussions. The new or “Interim Rule” provides the state and affected herd owners with some flexibility in how situations are handled.  
Wyoming State Veterinarian Jim Logan said in a recent news release, “We expect to have occasional brucellosis cases in our DSA since we have the last remaining reservoir of Brucella abortus in this country in the Greater Yellowstone Area. Livestock producers take many precautions to prevent exposure to wildlife, but there are some situations that even the best management cannot always avoid.”
As Logan is out of the office on medical leave, Meyer has taken the lead in the brucellosis cases.
The WLSB encourages producers not to panic, as the affected herds should be able to “test-out,” or slaughter only confirmed brucellosis infected animals, rather than slaughter their entire herds.
Echo Renner is a field editor for the Wyoming Livestock Roundup and can be reached at echo00@tctwest.net.