This month’s news that four Colorado dairy cows have tested positive for bovine tuberculosis (TB) underscores the sobering fact that the disease remains a threat to U.S. cattle herds.
Nationwide since 1998, at least 82 cattle herds and 10 captive cervid (deer) herds have been detected with bovine TB.
Despite the nation’s efforts to eradicate bovine TB, eight other states have detected it in herds in the last 12 years, according to the California Department of Food and Agriculture (CDFA).
Slaughter surveillance has detected 364 infected cattle since 2000: 34 infected adult cattle and 330 infected fed/fat cattle (75% were Mexican origin), CDFA reported in October 2009. The numbers don’t include the latest Colorado findings.
It’s the first time Colorado has seen TB in cattle herds “in quite a number of years,” Dr. Nick Striegel, Colorado’s assistant state veterinarian said June 24.
Investigation into the TB occurrence at the southern Colorado dairy is ongoing. “Over the next month, we will know more,” Striegel said.
While Colorado has been classified as free of bovine TB until now, other states haven’t been so lucky:
· California officials diagnosed seven cows from three Fresno County herds and one cow from a San Bernardino County herd with bovine TB in 2008. By late 2009, California had TB-tested approximately 419,000 cattle. Two herds were depopulated and over 8,000 cattle killed in the investigation. Two affected herds were put on a test-and-removal program.
In September 2008, California was classified as “Modified Accredited Advanced” (MAA). That status requires veterinarians and producers to check the TB requirements of receiving states when moving cattle out of California.
· Texas detected an affected dairy herd during private testing to sell the herd in 2009. Six infected cows were identified, with the strain type matching that detected in old roping steers of Mexican origin recently slaughtered from a nearby feedlot.
· Nebraska detected an affected cervid herd and an affected beef herd, both through slaughter surveillance, in 2009. Because they have different TB strain types, the infections were not related.
· Minnesota has detected 12 affected beef herds since 2005, and 27 infected free-ranging white-tailed deer. It received split-state status in September 2008 with a Modified Accredited (MA) zone around the affected herds and an MAA zone for the rest of the state.
· Michigan has detected 49 affected cattle herds and four cervid herds since 1998, says Bridget Patrick, risk management specialist for the Michigan Department in Agriculture. The state has three zones: the infected area classified as MA; the Upper Peninsula, which is TB-free; and the rest of the state as MAA. Infected free-ranging white-tailed deer continue to be detected, and infection has been found in several other wildlife species.
In late April, federal officials decreased the number of Michigan counties classified as MA “because we have a good program in place and more counties were eligible to move up in status,” Patrick says. Michigan is the only state, she adds, that requires every cow to have an electronic identification ear tag when it leaves the farm.
· New Mexico detected one new TB herd in 2008. The state has split-state status; an MAA zone around Curry and Roosevelt counties, and the rest of the state TB-free. Although there are no herds with TB at this time, federal rules require New Mexico to maintain its split-state status until next year, says Bobby Pierce, deputy director of the new Mexico Livestock Board.
· Indiana detected three infected cervid herds through slaughter surveillance in 2009. An investigation into a beef cow located two miles away infected with the same TB strain did not identify an affected herd.
· New York detected and depopulated a captive deer herd after a routine test was positive for TB in 2008.
TB is a contagious chronic bacterial disease that often doesn’t show signs until it has reached an advanced stage, according to USDA-APHIS Veterinary Services.
TB is difficult to diagnose with clinical signs alone. In the early stages of TB, clinical signs are not visible. In later stages, clinical signs may include: emaciation, lethargy, weakness, anorexia, low-grade fever, and pneumonia with a chronic, moist cough. Lymph node enlargement may also be present.
If you suspect TB in your herd, you should isolate the animal immediately and then call your veterinarian for a proper diagnosis, USDA-APHIS says.
The best way for cattle producers to prevent bovine TB is to maintain a closed herd or isolate and test purchased additions and cattle re-entering the herd, CDFA says.
· Maintain accurate records of animal identification and movements.
· Prevent contact with cattle of unknown tuberculosis status.
· Arrange professional diagnostic workup of sick animals.
· Establish a tuberculosis testing policy for employees.
Read more on Bovine TB:
Q&A: Bovine Tuberculosis Signs and Symptoms
USDA-APHIS Bovine TB Newsroom
Michigan Department of Agriculture - Reducing the Risk of Bovine TB