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June 9 2006


USDA: Much Still Unknown About Two US BSE Cases


WASHINGTON (Dow Jones)--The U.S. Department of Agriculture now believes the only two native-born U.S. cows to contract mad-cow disease were infected with a little understood and rare "atypical" strain that throws into question how the animals were infected.


USDA Chief Veterinarian John Clifford told Dow Jones Newswires this week that the latest two cases of BSE in the U.S. - found in Alabama and Texas  are abnormal, differing from the common form of the disease found in Canada and the U.K.


Clifford also said USDA has no plans to change the way it safeguards the U.S. beef supply.


An internal USDA memo stated, "There is no evidence to justify any changes in surveillance methods, disease control, or public health measures already taken in the United States."


Clifford agreed, saying, "Until the science proves otherwise, we'll be treating all of these cases as BSE and the normal, typical BSE, and we still feel confident that the safeguards we have in place are effective."


USDA regulations ban beef from non-ambulatory, or "downer," animals from the human food supply as well as require that some bovine tissue - such as brain and spinal cord material - considered to be risky for carrying BSE infection be removed before processing.


The U.S. also guards against cattle infection by  prohibiting the feeding of bovine material to cattle because of the belief that BSE is spread solely through contaminated feed.


But this "atypical" form of bovine spongiform encephalopathy found in the U.S. might not be spread through feed.


Clifford said he didn't know if the two U.S. cows were infected through contaminated feed - as most normal cases are - or whether they simply developed the disease spontaneously or by some other way.


There are different theories, Clifford said. "There may be spontaneous cases, but I can't say that there are or are not at this point in time."


Linda Detwiler, a consultant to major food companies and former Agriculture Department veterinary disease specialist, said, "There is so much that is unknown about the cases now."


There are several theories as to how cattle could develop an atypical form of BSE, if it even is BSE that the Alabama and Texas cows contracted, Detwiler said.


Transmissible spongiform encephalopathy, or TSE, is the umbrella neurological disease category that BSE - also called mad cow disease - falls under, together with the scrapie, traditionally found in sheep.


And one possibility, Detwiler said, is the cows could be contracting a form of sheep TSE, now believed to be transmissable to cattle.


Two things that do seem certain, she said, are that the atypical disease contracted by the two U.S. cows can transmit infection and it is detectable by current forms of testing.


She said French scientists have been successful in using atypical BSE to infect mice, but much is still unknown about transmissibility between cattle or if that is even possible.


The USDA memo said the abnormal BSE found in the Texas and Alabama cows "had different molecular characteristics (from normal BSE) that are similar to a few described cases in France."


Clifford, talking about the two infected native-born cows, said "there was abnormal prion protein present." And the cows' brains didn't have "the spongiform lesions that you would typically see" in the brains of a traditional BSE case.


"One important question," USDA said in the memo, "is whether the different types of atypical BSE are transmissible to cattle, and no such evaluations have been done."


The only traditional case of the more common variety of BSE found in the U.S. was discovered in Washington state in December 2003. That cow, according to USDA, was born and infected in Canada before being sent south to the U.S. Canadian and U.S. officials tracked down the source of infection for that cow and other Canadian animals to contaminated feed produced in western Canada.


But in regards to the native-born BSE cases, USDA said, "There are many unanswered questions about these unusual findings, and additional research is needed to help characterize the significance - or lack of significance - of any of these findings."


Source: Bill Tomson; Dow Jones Newswires; 202-646-0088;






































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