For good reasons, bovine tuberculosis (TB) is one of the most feared livestock diseases in the country. The U.S. campaign to eradicate bovine TB began in 1917 and virtually eliminated it in the second half of the century.
But the disease appears to be reemerging, evidenced by loss of TB-free status in Michigan, Minnesota, New Mexico and California. Oklahoma is currently TB free, but following a case in 2006, one more by 2010 would cause a status downgrade.
Veterinarians meeting recently at the U.S. Animal Health Association (USAHA) say it's time the U.S. beef and dairy cattle industries collectively begin taking this disease more seriously.
“I hear the beef industry screaming, but I don't hear the dairy industry screaming,” says Richard Breitmeyer, California state veterinarian. “There's a whole lot more we need to be doing than just screaming.”
In California, since December 2007, more than 145 herds and 200,000 cattle have been tested for TB — at a cost of nearly $16 million. Seven infected cattle have been identified.
Breitmeyer says the industry needs to begin immediately working harder in several areas:
- Better bovine TB diagnostics.
- Increased harvest plant surveillance.
- Attention to livestock biosecurity.
- Improved livestock traceability.
First, understand that Mycobacterium bovis, the organism that causes bovine TB, is very similar to the bacterium that causes human TB. And it can affect cattle, bison, deer and elk, along with other warm-blooded species.
More than 95% of bovine TB cases are transmitted through direct contact between cattle. Transmission via contamination of the environment hasn't been documented in the U.S. White-tailed deer in Michigan are thus far the only wildlife reservoir for bovine TB identified in the U.S.
If there are any smoking guns, they appear to be wildlife — deer — in the northern states and Mexican feeder cattle in California.
Minnesota has had 11 cases in cattle herds and 17 white-tailed deer cases since 2005. Michigan has had a large problem in its deer population, which spread to cattle and to at least one deer hunter. DNA testing shows two of the positive California cows share a strain of the bacteria originating in Mexico. In Mexico, M. bovis affects about 17% of cattle herds.
Biosecurity is the key
Chuck Massengill, Missouri state veterinary epidemiologist, says biosecurity is the key.
“Bottom line is that we can't allow animals that may potentially be TB-infected to commingle with breeding cattle — no contact, period,” he says. “This means all Mexican feeder cattle, ‘sport’ cattle and any other cattle of unknown origin unless they've been tested for TB.”
Massengill agrees with Breitmeyer that lack of organized interstate animal traceability is hindering the industry's ability to maintain vigilance on potentially infected cattle. They also agree it's a traceability issue as opposed to a trade issue.
“Once the imported cattle leave a border state like Texas or New Mexico, we lose our handle on them,” Massengill says. “If we know they're coming, we have a better chance of controlling their movement. But the way things are today, we have little clue when imported cattle are headed our way.”
Texas Animal Health Commission (TAHC) TB regulations went into effect April 1, 2008, requiring an approved ID device on dairy cattle being moved within the state. If an animal looks like a dairy animal, make sure it has an official ID device before it's moved within the state, stresses Bob Hillman, Texas state veterinarian.
“Dairy producers, calf raisers, feeders, or even beef cattle owners who have a few dairy animals, must comply with this cattle TB regulation that will aid in tracing cattle TB if it is introduced into Texas,” Hillman says. In October 2007, TAHC enhanced cattle TB and ID regulations for dairy animals entering from other states.
“USDA ear tags, which have been used in the brucellosis and cattle TB programs for years, are available from TAHC area offices at no charge for dairy cattle,” Hillman says.
Cattle owners who use these tags are to maintain a simple log of the animals tagged. Information is to include the date the tag is applied to the animal, tag number, and the animal's breed, sex and age. The record keeping can be as simple as listing the tag number, date and the animal's description.
Texas lost cattle TB-free status in 2002, but regained it in fall 2006 after employing a strategic plan that included TB testing of dairies and purebred beef herds and enhancing slaughter surveillance.
“Preventing the introduction of cattle TB is crucial. But we must be prepared to deal with infection, if it does slip through,” Hillman says. “Identifying dairy and dairy-cross animals will enable us to complete epidemiological investigations more quickly, so infection can be eliminated before it spreads to more herds.”
Clint Peck is director of Montana Beef Quality Assurance, Montana State University.