A century ago, bovine tuberculosis (TB) was responsible for more losses among U.S. farm animals than all other infectious diseases combined. Since state and federal agencies started tracking and eradication procedures in 1917, the disease has mostly been eliminated, but pockets of breakouts throughout the U.S. remain serious and costly for livestock producers.
A year ago, the U.S. Department of Agriculture, Animal and Plant Health Inspection Service and Veterinary Services released “Assessment of Pathways for the Introduction and Spread of Mycobacterium bovis in the United States – a study of the condition based on 2009 conditions.”
The study found that the biggest risk factors are the importation of cattle into the U.S. – both legal and illegal – and exposure to wildlife.
Retrospective epidemiologic analyses of outbreaks in four states (California, Michigan, Minnesota and New Mexico) identified several risk factors for the introduction and spread of bovine TB.
"In California and New Mexico, molecular fingerprinting techniques revealed several strains of Mycobacterium bovis (M. bovis), indicating multiple sources of introduction. Risk factors for California and New Mexico included the importation and commingling of Mexican-origin steers, management and biosecurity practices used by calf-raisers for dairy replacement heifers, and a large influx of purchased additions.
"In states with similar practices and risk factors, both beef and dairy herds are at risk for exposure to M. bovis.
Conversely, Michigan and Minnesota each had just one strain of M. bovis, indicating a point source of introduction and local area spread. The same strains were identified in the wildlife of each state, making cattle contact with infected white-tailed deer (especially contact with feed contaminated by deer) an important risk factor for the introduction and spread of bovine TB in those states and other areas in which infected wildlife reside.”
We asked experts in states where a TB outbreak had occurred to give us a current assessment of the disease. We also included some thoughts from someone who sees TB from a national perspective.
Let us know what you think by leaving a comment below or contacting the author, Karma Metzler Fitzgerald.
to email or call (208) 308-3185.
Rick Smith, DVM
Michigan Bovine Tuberculosis Eradication Program
Michigan Department of Agriculture and Rural Development
Beth S. Thompson, DVM
Minnesota Board of Animal Health
Dr. Annette Whiteford
New Mexico Livestock Board
Dr. Dave Fly
Jamie Jonker, Ph.D.
Vice President, Scientific & Regulatory Affairs
National Milk Producers Federation
Q. What is the status of TB in your state?
SMITH: Michigan has bovine TB endemic in the wild white-tailed deer population in a portion of four counties in the Northeastern portion of the Lower Peninsula. As a result of the TB in the wild white-tailed deer, we find one to three bovine TB-infected cattle herds annually.
Officially Michigan presently has three zones:
THOMPSON: As of October 2011, Minnesota is TB-free. However, the Minnesota Board of Animal Health and the Department of Natural Resources continue to work together in Northwest Minnesota. Within the 10-mile area where the TB-infected deer were found, the Board will continue at least one more year of testing and movement restrictions. The DNR will also test hunter-harvested deer during the hunting season of 2012.
- 72 counties are TB Free
- 7 counties are Modified Accredited Advanced (MAAZ) – occasional finding of infected wild white-tailed deer and infected cattle herds (Antrim, Charlevoix, Cheboygan, Crawford, Emmet, Otsego and Presque Isle counties)
- 4 counties are Modified Accredited (MAZ) – core area of infected wild white-tailed deer and infected cattle herds (Alcona, Alpena, Montmorency and Oscoda counties)
WHITEFORD: Currently there are 3 TB-affected dairy herds in Southern California. There have been 10 TB-affected dairy herds detected in California over the last 10 years. California is classified by USDA as Modified Accredited Advanced.
CULBERTSON & FLY: There are no cases and we are classified TB-free.
Q. What is being done to prevent further spread and contamination?
SMITH: The following steps are being taken:
- Surveillance TB testing in 11 counties where TB infections have been found
- Movement testing in TB areas
- Movement permitting of all animals moving from farms in 11 counties in TB area
- Radio Frequency Identification ear tags on all cattle at the time of TB testing or movement statewide
- Monitoring of cattle through markets and to slaughter
- Wildlife Risk Mitigation Project where farmers develop biosecurity plans for their farms with technical assistance provided by the project
- Mobile patrols
- Inventory reconciliation
WHITEFORD: Currently affected herds are quarantined and operate under a “test and removal” plan to eradicate bovine TB. All cattle moving out of the herd, moving into the herd and in contact with the herds are being traced and investigated for bovine TB. Sources of infection are being investigated.
CULBERTSON & FLY: New Mexico is unique in that we have such a strong set of laws and regulations dealing with movement control; we’re able to substantially limit the possibility of spread because we’re preventing unauthorized movement. As in most states, we continue to require TB tests on dairy cattle that come into the state. It boils down to a combination of good surveillance and a good regulatory structure.
JONKER: The current TB status of all states is maintained by the USDA and is available online.
Q. How have TB incidents in your state affected neighboring states?
SMITH: There is a variety of TB testing requirements that neighboring states have imposed upon Michigan cattle moving to their states. When an infected herd is found USDA Veterinary Services does traces on cattle coming from the affected herd, which at times includes cattle that have moved to other states.
CULBERTSON & FLY: It’s always a cooperative situation between the USDA and the states when there’s a discovery of a case. Like other states, we work with the federal government to do traces if a case is discovered. We determine where that cow’s been, whether there has been exposure, and if there’s a need to test other herds in other states if she came from another state.
Q. How have TB incidents impacted regulations relating to slaughter and cattle sales?
SMITH: For general cattle moving to slaughter there has not been much impact. For the occasional TB-positive herd that is in the process of depopulating, not all slaughter plants want to handle the remaining TB-test-negative cattle due to the enhanced surveillance required, which can slow their processes down.
The requirements of all cattle being tagged with a Radio Frequency Identification ear tag, and TB zone cattle needing to be current on their whole herd surveillance testing, as well needing a movement permit at times slows the processes at sale yards. Because of the disease some sale yards have a higher regulatory presence than they would otherwise.
THOMPSON: As Minnesota’s TB status dropped after the finding of TB-infected herds, the movement of cattle across state lines became more difficult. Some states required whole herd tests or movement tests. Even with split state status, Minnesota producers continued to see increased regulation for cattle movement.
WHITEFORD: It is a zoonotic disease. People can contract bovine TB through consuming illegal soft cheese products, unpasteurized milk and through respiratory exposure to live infected cattle or their carcasses. Humans infected with bovine TB can transmit disease to cattle. To prevent bovine TB, producers should:
WHITEFORD: All dairy cattle entering California require a TB test and regulations on Mexican event cattle are being enhanced.
Q. What should producers be aware of regarding this disease?
SMITH: If producers are buying cattle they should know the source of the animals they buy, they should be sure that all required testing has been performed, all required certification has been met, and that the animals are properly identified. In areas where the disease is not present in a wildlife population there needs to be prudence in adding cattle to the farm, and implementation of sound on-farm biosecurity procedures. In areas where the disease is present in a wildlife population, a biosecurity plan needs to be implemented that addresses the farm’s wildlife risks.
THOMPSON: Official identification and keeping good records is important for this disease, as it is with any disease. If a diseased animal can be traced back efficiently, producers and the involved agencies can save a lot of time, money and manpower. In Minnesota, the disease was found in both the cattle population and the wild white-tailed deer population; good management practices are also very important to stop the spread.
- Maintain a closed herd
- Mandate that calves and heifers raised off-site will not be exposed to or housed with feeder cattle
- Prevent contact between breeding cattle and feeder cattle, including in the sick pen
- Prevent contact with cattle of unknown TB status
- Isolate and test cattle entering the herd
- Establish a TB screening policy for employees
- Obtain TB-free herd accreditation
- Arrange professional diagnostic workups of suspicious, sick or dead animals
- Enhance disease tracing by recording animal identification and maintaining accurate records
CULBERTSON & FLY: The regulators can be helpful in terms of regulatory control, conducting the traces, and sharing information, but producers have the ultimate responsibility for their own herds. They need to be cautious about where they purchase additions to their herds. They need to make sure they’re dealing with reliable sources that practice good measures and require tests. And New Mexico dairy producers are doing just that; they’re being very proactive. We’re also seeing a shift in the industry: there are more closed herds now.
Q. Many have said these incidents prove that stricter traceability and
identification is necessary. Do you agree?
SMITH: Yes. In speaking with animal health officials from other states who have had to deal with TB traces coming to their states, virtually all of them expressed a desire to have the ability to trace animals that Michigan’s traceability program has.
THOMPSON: Good traceability is important when dealing with this disease. Knowing where a diseased animal has been and being able to track exposed animals will allow us to decrease the number of herds involved in an investigation and allows us to more efficiently respond.
WHITEFORD: Because TB is a disease that can be carried by cattle for years, potentially
spreading to other cattle before the animal shows signs of disease, knowing
where an animal has lived during the course of its life is critical.
CULBERTSON & FLY: Traceability is necessary, and there needs to be enough structure in every state to know where cattle have gone and where they’ve come from. New Mexico is a brand state, and we’ll continue with that. The brand is the basis for identifying cattle in New Mexico, and everything else (ear tags, etc.) is supplemental. Ear tags can be lost and they can be changed. The brand is absolute identification.
JONKER: The National Milk Producers Federation’s policy position supports “the establishment of mandatory animal disease traceability at the earliest possible date for reporting livestock movements in the U.S.” The USDA routinely takes more than 150 days to conduct tracebacks in a TB investigation which demonstrates our current system is not working. A national animal identification and traceability system is necessary for disease eradication programs (such as tuberculosis) and preparedness for catastrophic animal diseases (such as FMD). PD
Progressive Dairyman magazine
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