U.S. agriculture authorities have quarantined another herd of cattle in the state of Washington since a dairy cow there was diagnosed with mad cow disease last week. Officials say some of the cows will be killed.
A third herd in the northwest U.S. border state is now isolated after the U.S. Department of Agriculture found it contained a cow shipped from Canada with the diseased animal.
The other two quarantined herds include the infected cow's calves, and authorities say there is a slight chance of mother-to-calf transmission of the disease.
Eighty-one animals are thought to have arrived from Canada with the sick dairy cow, but the U.S. government has located only 11 so far, including those in the three herds.
The original cow has been slaughtered, and the U.S. Agriculture Department's chief veterinarian, Ron DeHaven, said the agency is considering whether to kill also those that came with her and others that subsequently lived on the same Washington farms.
"And I think it's safe to assume that at some point, that some or all of those animals will need to be sacrificed," he said.
Dr. DeHaven went on to say those that arrived with the sick cow might have been infected in Canada from the same feed more than six years ago. That was before the two nations imposed bans on feeding cattle parts to other cattle. Mad cow disease is believed to be transmitted this way.
But he concedes that the agency's concern with public fears might lead it also to sacrifice cattle that simply lived with the infected animal, even though mad cow disease is not contagious.
"The science would suggest that only those animals that have a direct link back to the premises of origin and would be birth cohorts of the infected cow represent any kind of risk at all, as well as the progeny from the infected cow," he said. "Having said that, it would be disingenuous if I were not to suggest that there is also some public perception concerns with other animals that might have been associated with those animals that would be of concern from a scientific or diseased transmission standpoint."
The Agriculture Department official says agency and cattle industry representatives will meet next week to discuss new U.S. government feed safety rules announced Tuesday. Under them, cattle too sick or crippled to walk can no longer be used for human food but must be diverted to pet food and other products. The department said those rule were being planned before the case of mad cow disease was confirmed last week.