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Two US BSE Cases From Rare Strain
Chris Clayton
DTN Staff Reporter
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Tue May 30, 2006 02:13 PM CDT
LONDON, England (DTN) -- The two cases of bovine spongiform encephalopathy found in
U.S. cattle over the past year came from a rare strain of BSE found largely in Europe
that scientists are just beginning to identify, according to research by a French scientist.
Researchers in France and Italy who presented their work at an international conference
in London have reported documenting two rare strains of BSE that are harder to detect
and affect mainly older cattle.
Thierry Baron of the French Food Safety Agency presented data to a group of about 250
scientists from more than 20 countries. According to the data, the 12-year-old Texas
cow that tested positive for BSE last June and the 10-year-old Alabama cow that tested
positive last March showed identical testing patterns to a small number of BSE cases in
France, as well as Sweden and Poland.
"They were identical," Baron said.
Scientists gathered in England over the weekend to discuss BSE research advancements
in the 20 years since England diagnosed the first case in cattle. No other country has
mirrored the mad-cow epidemic that England faced, which has led to more than 160
people contracting the human form of the disease and more than 184,000 positive cases
in cattle.
Bovine spongiform encephalopathy, or mad-cow disease, is a terminal neurological
disorder that affects cows. The scientific evidence shows in almost all cases it has been
contracted through contaminated meat and bone meal fed to the cow, typically at a
young age. However, scientists are now finding these "atypical" cases of BSE and
beginning to question if there has been a change in the abnormal protein that causes
BSE or if cattle may be susceptible to a "sporadic" BSE that would affect older cattle.
People contract a fatal form of the disease known as Creutzfeldt-Jakob Disease, which is
sporadic in older people, but the average age of death in the England cases was 29
years old, leading to the diagnosis of variant CJD. Those fatalities have been traced to
eating infected beef products.
Danny Matthews, head of transmissible spongiform encephalopathies at England's
Veterinary Laboratories Agency, said recent research on atypical cases of BSE raises
questions over whether older cattle can sporadically get the disease, or if there are more
strains of BSE than previously understood. Scientists may also be facing something new,
such as "son of BSE," he said.
"We don't fully understand what atypical BSE mean," Matthews said. "Is it spontaneous
or another source causing it? Time will tell."
While the test patterns in the U.S. cases and atypical cases in Europe closely matched,
Baron said there were no known links between any of the positive animals. The French
Food Safety Agency also sent a researcher to the United States to study the positive
Texas case and compare its results to known cases in France that did not match the
typical BSE positive tests.
"You could place them side-by-side and not tell the difference," Baron said.
Baron also raised the prospect that the disease could be sporadic in at least a small
number of older cattle. He acknowledged, however, such a conclusion would be hard to
determine through research because of the small numbers of cattle with this atypical
strain globally.
"It would be very hard to prove," he said.
A German researcher also reported at the conference that testing has uncovered at least
one atypical case of BSE in his country from an older cow that appeared similar to the
atypical cases reported by Baron.
If these atypical cases are sporadic, then that validates the strength of USDA's
ruminant-to-ruminant feed ban and demonstrates that an infectious agent is not
spreading through the cattle population.
Last month, U.S. Secretary of Agriculture Mike Johanns announced a risk analysis by
USDA showed there may be five to seven potential cases of BSE in the U.S. cattle herd
of more than 93 million cattle, based on the USDA's enhanced surveillance testing over
the past two years. Johanns said testing numbers would soon be reduced but he didn't
give an actual figure on the number USDA would test annually.
Art Davis, a USDA scientist for the Animal and Plant Health Inspection Service at the
National Veterinary Services Laboratory in Ames, Iowa, said in his presentation Sunday
the Texas and Alabama test results showed completely different testing signatures than
the Washington state case in December 2003. The Texas and Alabama cases showed
"unusual molecular" prion patterns compared to the typical BSE case, Davis said.
"The classical lesions were not there," Davis told the audience.
Davis, a last-minute replacement presenter for another researcher who was unable to
attend, later said he had not seen the research suggesting the U.S. cases were atypical
until Baron shared his report. Davis said the French researchers worked with staff from
the Agricultural Research Service so APHIS staff may have been unaware of the work.
Linda Detwiler, a former USDA researcher also at the conference said she and other U.S.
researchers were stunned by the report.
The Texas case last June caused USDA to change its testing protocols because USDA
officials initially announced the case as inconclusive, then negative in November 2004
using the USDA's standard immunohistochemistry testing protocol. The Texas case was
only reversed and declared positive after the USDA's Inspector General ordered a new
test on the suspect cow's brain stem using a different test, the Western Blot, which is
the confirmatory test used in England. That came back positive.
Still, Davis told other scientists it was difficult to recognize the case. Half the samples
from the Texas cow tested negative using the Western Blot test.
To validate the difference between atypical and typical cases, Baron said researchers
also used test mice to study the incubation periods of the two strains. The atypical cases
had a longer incubation period before the mice showed clinical signs of the disease.
Chris Clayton can be reached at [email protected]
(CZ)
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