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[Fwd: [Fwd: [riskanal] RE: Anthrax testing]]
There has been so much interest in anthrax that the following email from
the Risk Analysis listserv seemed especially helpful regarding anthrax
testing. My thanks to Dr. Betty Jensen and the Risk Analysis
professional
Sincerely,
Maury Siskel maury@webtexas.com
================================
-------- Original Message --------
Subject: [riskanal] RE: Anthrax testing
Date: Wed, 17 Oct 2001 09:12:21 -0400
From: "Jensen, Betty K." <Betty.Jensen@pseg.com>
Reply-To: "Jensen, Betty K." <Betty.Jensen@pseg.com>
To: "Mailing List for Risk Professionals" <riskanal@lyris.pnl.gov>
Below are excerpts from today's (10/17/2001) WSJ which sheds some light
on the issue. You can probably get the entire article from the web.
Questions of Security: Nevada Case Illustrates Difficulty in Identifying
Anthrax --- CDC's Preliminary Tests on Microsoft Letter Are Negative,
Contradicting State Results
By Laura Johannes and Rebecca Buckman
10/17/2001
The Wall Street Journal
A6
"The doubt over the Nevada case highlights the resulting confusion when
harried labs struggle with a suddenly expanded workload. It also
illustrates what some experts have been saying privately for weeks:
Testing for anthrax isn't always a black-and-white matter. The anthrax
bacteria, Bacillus anthracis, looks, and often behaves in tests, a lot
like its harmless cousins, B. cereus, B. subtilis and B. thuriengensis"
"As many as a dozen tests can be needed just to determine whether
anthrax is present, let alone identify the specific strain. No single
test alone can identify anthrax but "a decision tree with other events
allows you to start to narrow it down," said Calvin Chue, a research
scientist at the Johns Hopkins Center for Civilian Biodefense Studies."
"Dr. Todd said tests done at the Nevada State Health Laboratory
included a "capsular staining test," which uses a special dye to
illuminate a distinctive sugar found on the outside of anthrax, and
the "gamma phage test," in which the sample is subjected to a virus
that has the ability to cut up anthrax but not many other types of
bacteria."
"However, Dr. Chue, who served as a consultant to the U.S. government
in the mid-1990s testing soil in Iraq for evidence of biological
weapons, said those tests alone may not be enough. "I wouldn't be
at all certain right now," Dr. Chue said." "Michael Osterholm, a
bioterrorism expert at the University of Minnesota, added, "I'd
reserve judgment before I said `yes,' " to the presence of anthrax
in Reno."
"Adding to doubts, even the Reno sample that was viewed as an
overall positive by state officials failed an important "fluorescent
antibody" test, in which a protein known to bind to anthrax is
dyed green, then applied to the sample to see if it sticks. That
test is very hard to read, but is considered a critical part of
identifying anthrax. Officials at Nevada's lab couldn't be reached
for comment."
"The CDC spokesman was unable to provide detailed information about
its testing procedures yesterday. However, experts familiar with
its labs say technicians there will likely perform more
sophisticated tests, such as an Elisa test, which uses antibodies
that bind to anthrax. The lab also will likely do a test called a
"polymerase chain reaction," which is considered a gold standard
for identifying anthrax; that test compares known genetic
sequences of anthrax to DNA in the sample."
"Identifying Anthrax
A battery of tests are needed to confirm the presence of anthrax. A
mystery sample is first put on a nutrient plate and given eight to 12
hours or more to grow. Then an initial set of basic tests can
determine the probability of anthrax, but some combination of further
tests is needed for confirmation.
Basic Tests
-- Eyeball test: Anthrax looks like a bunch of rods linked
together like cars in a train. But other bacteria look like this too.
-- Gram-Positive: Anthrax has a particular type of cell-wall
structure that shows up purple on a simple dye test. Again, many
other bacteria will show up purple.
-- Gamma Phage: A type of virus, called gamma phage, can easily cut
apart anthrax. The phage leaves many types of bacteria alone.
-- Capsular Staining: Anthrax is surrounded by a sugar capsule
which shows up as smooth and glassy when treated with a special dye.
Many other bacteria look rough and jagged along the edges.
-- Motility: Many types of bacteria tend to swim around in
liquids, but anthrax generally stays put.
-- Beta Hemolysis: Some bacteria cut up blood cells taken from
sheep, but anthrax doesn't do this.
Antibody Tests
-- Fluorescent Antibody: The sample is flooded with an antibody,
which has been dyed fluorescent green, then washed; if it sticks,
it's likely anthrax. But this test can sometimes be hard to read.
-- Elisa (Enzyme-linked immunosorbent assay): Uses two separate
antibodies to test the sample. It also uses numerous "controls," in
which known anthrax and other bacteria are subjected to the test.
Genetic Tests
-- PCR (Polymerase chain reaction): Involves testing short
stretches of genetic material to compare with the known genetic
sequences in anthrax. Only certain labs can do this test, including
the Centers for Disease Control and Prevention. It's considered
the "gold standard" and is rarely wrong.
-- DNA Sequencing: This is one of the best tests, but very few
labs can do it; the CDC and the U.S. Army lab at Fort Detrick, Md.,
can, however.
Sources: Johns Hopkins Center for Civilian Biodefense Studies,
Southern Research Institute."
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