ProMED-mail |

Published Date: 2005-06-12 23:50:00
Subject: PRO/AH/EDR> BSE, bovine - USA (03): susp.
Archive Number: 20050612.1637

BSE, BOVINE- USA (03): SUSPECTED
********************************
A ProMED-mail post
<http://www.promedmail.org>
ProMED-mail, a program of the
International Society for Infectious Diseases
<http://www.isid.org>
[1]
Date: 11 Jun 2005
From: ProMED-mail <promed@promedmail.org>
Source: Reuters via MSNBC [edited]
<http://msnbc.msn.com/id/8182017>

USDA uses 3 mad cow tests on suspect animal
-------------------------------------------
A U.S. animal tested positive for mad cow disease and additional tests will
have to be done at a British laboratory to confirm the results, the U.S.
Agriculture Department said.
The USDA has used at least 3 different tests on the current suspect animal with
varying results. Due to the uncertainty, the department has decided to send
brain samples to a reference laboratory in Weybridge, England, for confirmatory
testing. USDA will also conduct further testing, which will take several days
to complete.
The only U.S.-confirmed case of mad cow disease, or bovine spongiform
encephalopathy, was found in December 2003 in Washington state dairy cow.
The USDA reported on 18 Nov 2004 [see ref. at end, - Mod.JW] that the suspect
animal tested "inconclusive" in 2 rapid screening tests. The quick tests,
referred to as ELISA, take only a few hours to identify whether abnormal prion
proteins are present in an animal's brain tissue sample. Misfolded prions are
believed to be the cause of BSE, which slowly disintegrates neural tissue and
is always fatal.
To test an animal carcass using the rapid test, scientists snip off a small
amount of the brain stem for testing. A reagent mixture consisting of digestion
enzymes is used to isolate the BSE-specific prion protein in the sample.
Antibodies are then added to the sample to detect the prions. A chemical is
then added to the sample that enables it to emit light, and the light is
measured by a computer. In general, a negative sample is white and a positive
is yellow.
IHC tests
---------
The USDA reported on 23 Nov 2004 that the suspect animal tested negative in 2
IHC tests. The immunohistochemistry test, or IHC, involves a staining
technique to determine whether the brain sample has the BSE agent.
After placing antibodies on a suspect brain sample, the test causes a chemical
reaction that can detect the abnormal form of the prion protein found in BSE.
The test, considered the "gold standard" by the USDA, requires 2 to 3 days to
complete.
Western blot test
-----------------
The USDA's Inspector General earlier this week recommended that the department
retest the suspect animal using the western blot test. The USDA reported on
Thursday that the sample returned a "weak positive" for mad cow disease and
would need additional testing.
The test, arguably more sophisticated than the IHC test, homogenizes a suspect
brain sample and treats it with a protease enzyme that destroys normal prion
proteins, but not the abnormal protein. The sample is then run through a gel-
type separation using specific antibodies that will give bands. The USDA said
the molecular weights of those bands are used to determine the outcome of the
test.
These tests typically take 1-2 days to complete.
--
ProMED-mail
<promed@promedmail.org>
******
[2]
Date: 11 Jun 2005
From: ProMED-mail <promed@promedmail.org>
Source: AP via MSNBC [edited]
<http://msnbc.msn.com/id/8183299>

Q&A About Mad Cow Disease
-------------------------
New suspicions of mad cow disease in the United States have arisen from a fresh
round of testing on 3 cows that were cleared of infection last year [2004].

Results for one of the 3, a beef cow, indicated the existence of the disease,
the Agriculture Department said Friday. Now more tests are being done.
Regardless of the findings, the government says there is no health risk to
humans or animals.
Q: Can I get mad cow disease?
A: Not from this animal, because it did not get into the food supply. It was
a "downer" cow, unable to walk. The government banned downer cows from the food
supply just days after the 1st case of mad cow disease turned up in the United
States.
Also banned are tissues from older cows believed to carry the disease,
including the brain, skull and spinal cord. Those materials must be removed
from slaughtered cows older than 30 months, because it's believed that
infection levels increase with age.
Q: What is mad cow disease?
A: Formally called bovine spongiform encephalopathy, or BSE, mad cow disease
happens when proteins in the body bend into misfolded shapes called prions.
Prions deposit plaque that kills brain cells, leaving spongy holes in the brain.
People can get a form of the disease, called variant Creutzfeldt-Jakob disease,
by eating contaminated meat. The disease has killed about 150 people worldwide,
mostly in Britain, where there was an outbreak in the 1990s.
Q: Why were there conflicting test results?
A: Different tests were used. First, initial screening called "rapid tests"
indicated the potential for mad cow disease in 3 cows. Rapid tests look for BSE
by removing normal proteins, then adding chemicals that bind to the abnormal
BSE protein, producing a change in color or some other noticeable difference.
Following the rapid test results in June and November 2004, the government did
further tests using an "immunohistochemistry," or IHC, technique. IHC stains
brain tissue samples to highlight the mad cow protein, and scientists examine
the samples for telltale lesions.
Last week, it did tests using an "immunoblot" or western blot technique.
Western blot destroys normal protein to leave only the abnormal mad cow protein
present.
Q: Why did the government decide on new tests?
A: Last week, the Agriculture Department inspector general recommended another
set of tests. The inspector general's office is an independent arm of the
department that performs audits and investigations.
Officials did not say why the inspector general called for more testing.
Q: Which test is better?
A: The Agriculture Department says both tests are accepted by the World
Organization for Animal Health.
Q: How many cows has the U.S. tested?
A: Since the 1st case of mad cow disease turned up in December 2003 in
Washington state, about 375 000 animals have been tested for the disease,
primarily those that appear sick. The nation's cattle herd numbers 96 million.
There is no test to detect the disease in live animals.
Q: Could another cow get mad cow disease?
A: Not from this animal. The only known way the disease spreads is through
feeding infected cattle remains to other cattle. The U.S. banned the use of
cattle parts in cattle feed in 1997.
Experts inside and outside the government are concerned about loopholes in the
feed ban. For example, cattle remains can go into poultry feed. Poultry litter,
which includes uneaten and digested feed, can then go into cattle feed.
Scientists say the BSE agent could survive and be fed back to cattle.
Q: What happens now?
A: A sample is being sent to an internationally recognized laboratory in
Weybridge, England, that provided independent confirmation of the 1st U.S. case
of mad cow disease. The Agriculture Department also will conduct further tests.
[Byline: Libby Quaid]
--
ProMED-mail
<promed@promedmail.org>
******
[3]
Date: 11 Jun 2005
From: ProMED-mail <promed@promedmail.org>
Source: U.S. Department of Agriculture Department website [edited]
<http://www.usda.gov>

[Excerpts]
The government says there is no new health risk from mad cow disease despite
fresh suspicions about an animal that was previously cleared of the lethal
infection.
The Agriculture Department said Friday night it will seek further testing of a
tissue sample from a "downer" beef cow (one unable to walk) after receiving
conflicting results on tests of it for mad cow disease.
Only one case of mad cow disease has been confirmed in the United States, in a
dairy cow in Washington State in December 2003. Since then, preliminary tests
indicated the existence of the disease in 3 cows, but further testing had ruled
out any infection.
USDA decided this week to perform additional tests, and one of those 3 -- a
beef cow -- turned up positive. Johanns said the department's inspector general
had recommended the additional testing, but the secretary did not say why.
A sample from the animal was being sent to an internationally recognized
laboratory in Weybridge, England, that provided independent confirmation of the
1st U.S. case of mad cow disease. The Agriculture Department will also conduct
further tests.
The officials could not say whether the cow was born in the United States. The
Washington state animal had been imported from Canada, which has had 3 other
cases of mad cow disease. Investigators never located all 80 of the cattle that
crossed the border into the United States with the infected animal.
--
ProMED-mail
<promed@promedmail.org>

See Also