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;
bill.tomson@dowjones.com
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