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Animal Health

Producers say Strain 19 vaccine needs reconsidered

Written by Cat Urbigkit
Pinedale ­– It’s a question of acceptable risk. Is it an acceptable risk to use the RB51 brucellosis vaccine when we continue to have brucellosis outbreaks? Or is the better choice ­– the more acceptable risk – to reauthorize the use of Strain 19 in western Wyoming cattle herds while knowing it causes false-positive reactors that must be slaughtered to determine if they were actually infected with the disease?
    Sublette County cattlemen maintain that federal animal health regulations don’t reflect today’s brucellosis reality. The regulations provide for the state to lose its brucellosis-free status if the infected herd is not completely depopulated within 60 days. But the producer knows that even if his entire herd is slaughtered and he restocks his ranch, the threat of disease transmission hasn’t been reduced one bit. That’s because he lives in western Wyoming’s Greater Yellowstone Area, home of the wild reservoir for brucellosis: wild elk and bison.
    Wyoming State Veterinarian Walt Cook said the Sublette County herd owner, desperately trying to figure out how to save the herd he’s tried hard to build, is “a victim of antiquated regulations.”
    USDA Animal and Plant Health Inspection Service’s Bret Combs said his agency’s preference is to depopulate entire infected herds, rather than having the herd owner enter into a long-term quarantine and testing program. Combs said in the Sublette County case, “The disease still exists there,” even after the cattle are gone.
    “How much sense does it make if you’re not going to address the source?” Combs questioned.
    Sublette County cattlemen called for an exception to the rules that would allow cattle herds in this high-risk area of western Wyoming to use Strain 19, which they feel has the ability to provide greater protection to their herds than RB51.
    Bondurant’s Kevin Campbell said years ago, before brucellosis vaccination was mandatory, producers using Strain 19 had elk on their winter cattle feedlines and brucellosis was a rarity in their cattle herds. Now that vaccination is mandatory, and RB51 is the only option, western Wyoming has had recurring brucellosis outbreaks in cattle herds.
    Animal health officials pointed to the weakness of Strain 19 in that it causes false-positive test results, and that cattle must be destroyed to learn if they actually contracted the disease. Local cattlemen pointed out it’s preferable to have to kill a few false-positive cows than to slaughter entire breeding herds because of RB51’s failure to provide protection.
    The meeting brought more than 100 producers to town to discuss the current brucellosis situation on June 17, but much of the discussion turned to the vaccine.
    While Strain 19 and RB51 provide about the same protection in the short-term, producers learned at the meeting that RB51’s effectiveness wanes after about three years. The two cows that were destroyed last week were estimated to be about four years old, and had been calfhood vaccinated with RB51.
    Animal health officials are recommending adult cows be booster vaccinated with RB51 every few years in western Wyoming’s high-risk area. RB51 has been in use nationwide for about 10 years, so producers and animal health officials are beginning to learn the long-term effectiveness of the newer vaccine.
    Cook has the ability to request APHIS consider an exception to federal rules to allow the use of Strain 19 in that corner of Wyoming. Whether APHIS would grant such a request is unknown. The issue is expected to receive additional discussion in the coming weeks as the state struggles to deal with the current brucellosis outbreak.
    Meanwhile, the Daniel-area cattle herd where the two infected cows originated was bled for testing last June 18 and animal health officials were preparing plans to quarantine and test all contact herds, as well as bulls sold from the original herd. At this time in the epidemiological investigation it is unknown how far the testing net will be cast.
    Cat Urbigkit is a correspondent for the Wyoming Livestock Roundup.