SALEM, Ohio – Eighty-nine cows and 16 workers have tested positive for bovine tuberculosis exposure at a 3,700-cow dairy farm in Tulare, Calif.
The exposed cattle have been killed and an autopsy revealed one had a lung infection, meaning it was the only cow capable of spreading the disease by air. Approximately 30 others had infected lymph nodes.
The rest of the herd has been quarantined.
The California Department of Food and Agriculture is testing additional herds that have been in contact with the infected animals. This includes testing herds that have purchased animals from the dairy within the last 18 months.
In order to determine the origin of the tuberculosis, all animals the dairy has purchased within the last eight to 10 years will be examined.
Transfer. Airborne exposure through coughing and sneezing is the most common way animals transfer the bovine tuberculosis to each other and to humans; however, it can also be transferred through consumption of contaminated water, feed or milk, according to the Ohio Department of Agriculture.
“Dairy workers may contact bovine TB while in close contact with an infected animal, or by drinking raw milk from an infected animal,” said California’s agriculture department. “The exposure risk beyond the affected dairies is minimal.”
There is no economical vaccine or treatment for tuberculosis in cattle, said Lee McPhail, assistant chief of the Ohio Department of Agriculture’s Division of Animal Industry.
Close to home. Ohio achieved tuberculosis-free status Sept. 19, 1990, and the last reported case in the state was in 1985, McPhail said.
Although tests are not routinely conducted for tuberculosis, the disease is still monitored, McPhail said.
“Slaughter surveillance” is conducted on all slaughtered animals. If signs of tuberculosis are found, further examination is conducted and a trace is conducted to the farm of origin, McPhail said.
Some auctions, sales and interstate movement also have testing; however, “the primary way to test is by looking at cull cows as they go to slaughter,” said Bill Shulaw, Ohio State University veterinarian.
Losing freedom. California is not yet in danger of losing its free status, McPhail said, unless tuberculosis is found in more herds within the state. The disease must be found in two or more herds within a specified period of time before the state can lose its status.
When tuberculosis is found in a cow, all circles around the animal are tested, including other animals on the farm and the herd where the animal originated.
When a state loses its TB-free status, the biggest burden is increased testing for moving animals, Shulaw said.
When an animal from an infected state is transferred to another state, an individual tuberculosis test must be done on the animal. In addition, a tuberculosis test must be done on the entire herd of origin, Shulaw said.
Tuberculosis was the main reason milk pasteurization began in the early 1900s, he said. People were drinking milk that had not been boiled and, therefore, contracted the disease from the milk of infected animals.
“Pasteurization virtually eliminated [the disease],” Shulaw said.
TB elsewhere. Texas lost its free status earlier this month after two herds tested positive for bovine tuberculosis. Therefore, Texas breeding cattle transported out of state must test negative for tuberculosis and be officially identified.
Michigan lost its free status several years ago when white-tailed deer and cattle tested positive for the disease.
(You can contact Kristy Alger at 1-800-837-3419, ext. 23, or by e-mail at firstname.lastname@example.org.)
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