USDA Scientists Amplify Genetic Secrets To Detect Animal Diseases
WASHINGTON. D.C.
Amplify a radio wave and inaudi
ble signals become sounds, such as
music or speech. In the same way,
a new technology based on a
polymerase chain reaction (PCR)
is amplifying hidden genetic infor
mation to reveal animal diseases
that have been difficult to detect
Since the discovery of PCR in
1985, the U.S. Department of
Agriculture’s Animal and Plant
Health Inspection Service
(APHIS) has been putting the PCR
technique to practical use in the
laboratory. APHIS also is involved
in licensing commercial produc
tion of the diagnostic kits that
make use of the process.
“Disease organisms may be pre
sent in an animal at a very low
level, especially in the early stages
of infection," said David Espeseth,
who heads the licensing division in
APHIS. “Detecting these organ
isms can be like hunting for a cer
tain piece of a jigsaw puzzle. PCR
technology provides a way to amp
lify the target piece exactly, many
times over, so that the chances of
finding it are greatly increased.”
The technology relies on look
ing closely into the organism’s
DNA its genetic blueprint.
Since each blueprint is unique, it
reliably reveals the identity of its
owner.
“PCR doesn’t amplify the entire
DNA complement It focuses on
one unique, detectable sequence,”
Espeseth said. “It’s like duplicat
ing just the needed edge of the
target puzzle piece. This is spee
dier and more efficient than old
propagation methods that repli
HEY!
4 e fsih-HAY DEMO. DAY—to°j?(K)
2240 MOWER CONDITIONER
★ ADDED ATTRACT!
1470 BALER
„ „ „ _ - . - T Umberger’s Of Fontana, Inc.
Lebanon Valley Implement Co., Inc. Rt 4 Box 545 Lebanonj PA 170 42 717 « fi7 - Ifil
700 E. Linden Street, Richland, PA 17087 8 m || es E . of Hershey on Rt. 322 7i7-»b7-sibl
717-866-7518 “Serving the Agriculture Community Since 1932 M
cated an entire organism."
Once scientists identify the
unique sequence that will reliably
indicate the presence of the disease
organism, they synthesize a com
plementary DNA sequence called
a DNA probe. If the disease organ
ism is present in a test sample, the
targeted sequence will pair with
the DNA probe. A color change or
radioactive glow built into the
DNA probe confirms the disease.
“DNA probes have been used
for some yean and are extremely
accurate,” said Espeseth. “The
pairing never happens if the dis
ease isn’t present Without ampli
fication, however, DNA probes
aren’t very sensitive. Amplifying
the DNA with PCR techniques
produces a very specific and very
sensitive test for the presence of
animal disease organisms.”
Espeseth’s group recently
licensed the first PCR-based diag
nostic test kit which is now com
mercially available. It identifies
the bacteria responsible for para
tuberculosis (or Johne’s disease),
which is a chronic, contagious,
incurable disease of ruminants.
The PCR-based test takes 24 hours
much less than the existing test
which depends on bacterial cul
tures and takes about 10 to 12
weeks.
In the future, PCR tests also
promise to support the fight
against pseudorabies, a contagious
viral disease of swine that spurred
American pork producers to call
for a nationwide eradication prog
ram that began in 1989. Develop
mental work on PCR is being con
ducted at the National Veterinary
Come S
Services Laboratories (NVSL) in
Ames, lowa.
“Pseudorabies can be carried by
an apparently healthy pig, which
may suddenly begin to shed the
virus, infecting others in the herd,”
said Jon Katz, who heads a team of
APHIS microbiologists at NVSL.
“Available diagnostic tests scan
for antibodies or infectious viruses
but may miss latent infections that
will be caught by PCR techniques.
The gain in accuracy could help
the swine industry rid itself of the
disease more quickly.”
At its current stage of develop
ment, the PCR technique for
pseudorabies testing has a major
drawback. It requires brain tissue,
which necessitates sacrificing the
test animal. Katz said his team is
working on an adaptation that
would use tonsil tissue instead.
PCR technology also is being
adapted for detecting foot-and
mouth disease, one of the world’s
most destructive illnesses of lives
tock. This highly contagious viral
disease has been successfully kept
out of the United States for the last
several decades. If the disease ever
bypassed APHIS inspectors at the
border and started infecting U.S.
livestock, APHIS would take
prompt countermeasures the
success of which would depend on
early, accurate detection of the
virus.
Richard Meyer is an APHIS
microbiologist at Plum Island
Foreign Animal Disease Diagnos
tic Laboratory, located offshore
near Orient, N.Y., with highly sec
ure facilities that make it safe to
work with exotic disease organ-
BM— ■ ■ ■ (g)
■■■a ■■■■ I
■■■■■ ■ ■ mmmm
This Equipment In
264 ROTARY RAKE
: ROUND BALE WRAPP
HOST: John D. Cassei & Sons
Harrisburg
RED TOP ROAD .7 Ml.
SB-^EI
Harrisburg
US 22
Hershey
US 422
isms. Meyer and his coworkers
have developed a PCR test for
foot-and-mouth disease that can
confirm or deny the presence of the
disease in a fraction of the usual
time. The PCR procedure can be
accomplished in a plastic tube,
while the confirmatory diagnostic
procedure requires sacrificing a
live animal.
Despite the promise of PCR pro
cedures, laboratory workers aren’t
about to throw away their tradi
tional test tubes and culture plates.
Even in situations where PCR pro
cedures are practical, they require
Md. Ag Still
ANNAPOLIS, Md. Mary
land Secretary of Agriculture
Wayne A. Cawley, Jr. has
announced that since Governor
William Donald Schaefer’s trade
mission to Eastern Europe and the
Soviet Union last spring, his
department, along with the Uni
versity of Maryland, has continued
to build strong ties with these
countries.
“In Poland, Hungary, Romania,
and the Soviet Union, we have
increased our contacts and
exchanges. Our follow-up from
the Governor’s trip has been fan
tastic,” Cawley said.
“In January, my department and
the university hosted the governor
and a delegation from Poznan,
Poland. An immediate result of
their visit is a serious effort by a
Maryland poultry processor to
further explore a joint venture in
the poultry area,” said Cawley.
“In Hungary, we are working
with an American businessman on
Action:
* 0 :'v
' ’ v *. v v ."'’"t:***
«*-» ► * ,*, \ *M *, \v>
.&&»m . /, >_ i. - ' ' * • " " -
2170 MOWER CONDITIONER
DEMONSTRATION ★
Allentown
Lebanon
thrata
Lancaster Farming Saturday, Hay 11,1991*05
sophisticated training and equip
ment. which results in increased
operating costs. However, at
times, the procedures already offer
immediate savings, as in the case
of foot-and-mouth disease tests
where a plastic tube can replace a
cow.
“The scientific community is
excited by the potential of PCR
techniques,” Espeseth said. "We
are finding applications in all
fields of medical technology
where DNA identifications can
furnish crucial evidence.”
Going Strong
developing a 6,000-acre farm. The
University of Maryland System
sent three experts to Hungary at the
expense of the Hungarians to help
on the project. The potential is
unlimited,” Cawley said.
Deputy Secretary of Agriculture
Robert L. Walker met with the
Romanian Ambassador in
Washington. As a result, the
Minister of Agriculture from
Romania invited two of the depart
ment’s animal health experts to
visit Romania at the expense of the
Romanian government The trip
took place last fall and laid the
groundwork for future business
contacts.
The department’s most exten
sive contacts have been with vari
ous Soviet organizations. Mary
land farmers hosted 10 students
this past summer from the Timi
ryazev Agricultural Academy and
the Moscow Institute of Agricul
tural Engineers.
1310 BALER
HEY!