The Rural Voice, 1992-03, Page 16FARM GATES
• All sizes from 4' - 20' in stock
• 1" x 1" tubing • 7 -bar gates
a complete line of
new- Ijfe feeds
••?‘". -
L ALLAGNER Fencing
Amo`
• Sales • Installation
• Free estimates
CARSON'S FEED
AND FARM SUPPLY
Highway 86 E., LISTOWEL
519-291-1094
MONOWAY FARMS
Limited
LANDRACE
HAMPSHIRE
YORKSHIRE
DUROC
Completely Closed Herd
Herd Health Classified "Good"
We have a good selection of bred
gilts for March and April
Limited Time Offer:
With the purchase of a boar or
5 F1 gilts you will receive a $50.00
coupon redeemable towards the
purchase of your next boar.
Offer expires May 1, 1992.
Farm located 6 miles west of Brussels
on County Road #16
Wayne or Paul Fear
Phone: 519-887-7477
Fax: 519-887-9837
QS Rep. Don Ruttan 519-887-9884
12 THE RURAL VOICE
DIAGNOSTICS
NEW DIAGNOSTIC TESTS
by DR. S. E. SANFORD
VETERINARY LABORATORY SERVICES
New tests are a necessary part of
the delivery of diagnostic medicine.
Conventional, time -tested methods
are often time-consuming: culture and
identification of disease agents may
take from several hours (parasites),
one or two days (most routine bacter-
ia) to two or three weeks for most
viruses. Worse yet, if the organism is
not there or will not grow, the search
may be prolonged considerably be-
fore a negative answer is given.
Most of us have heard of Fluores-
cent Antibody (FA) techniques where
a dye (fluorescene) is combined with
antibody, then poured onto tissue
where it seeks out and attaches to a
disease agent, if present in the tissue.
The disease agent is then identified
by looking through a special FA mic-
roscope. This method can be rapid
and reliable but still has many short-
comings, not least that it is technical-
ly challenging. FA has a tendency to
cross-react with other materials in the
sample, causing possible misdiagno-
sis.
Some of the disease agents cur-
rently identified using FA include:
IBR, BVD and BRSV viruses in cat-
tle; TGE in pigs; and ILT in poultry.
Many of the newer tests I am about to
describe use more sophisticated
versions of the FA concept to more
easily and reliably identify an agent.
Some tests include: ELISA, Latex
Agglutination (LA), Monoclonal
Antibody, Immunoperoxidase (IPx)
and Nucleic Acid Hybridization/DNA
Probes. Most of these are currently
used in veterinary diagnostic labora-
tories in Ontario; others are at the
door but need modifications before
they can be used routinely.
ELISA Tests: At the start of the
last decade, Enzyme Linked Immuno-
sorbent Assay (ELISA) was little
more than a jumble of unpronounce-
able words to most people. By the
end of the decade ELISA tests had
been installed in our laboratories and
were being used routinely to monitor
diseases, especially in poultry. New
Castle Disease, Bursal Disease, Avian
Bronchitis, Reovirus and Avian Ence-
phalomyelitis are all monitored this
way. Adaptation of ELISA for com-
mon swine diseases can be expected
during this decade. ELISA tests are
also used to identify mycotoxins in
feed, antibiotic residues in meats, and
even for the HIV (AIDS) virus in
human blood.
Latex Agglutination (LA) Tests:
This test has been incorporated in our
laboratories to identify rotaviruses in
scouring calves, sheep, goats and
pigs. Because of its speed and accu-
racy it has considerably shortened the
time taken to diagnose rotavirus ente-
ritis in these species. Another advan-
tage is that the LA test can be done on
fresh faeces which means a whole
animal does not have to be submitted.
One shortcoming is that it can identi-
fy only one type of rotavirus (Type
A). This works well for calves, sheep
and goats since only Type A affects
those species; but not so well for pigs
which can be infected by Type A and
at least three other types.
Monoclonal Antibody Tests: Mo-
noclonals are very specific antibodies
and can be used for any of the tests
that use antibodies. Their use so far,
however, has been restricted because
they are so specific. As a result, they
are currently being used in cases
where cross-reactions have been sus-
pected and a very specific antibody is
needed to ensure that there is no
confusion due to cross-reaction.
Immunoperoxidase (IPx) Tests:
almost identical to FA tests except
that they can be performed on histolo-
gical tissues, making them more ad-
aptable, and easier to use and inter-
pret. IPx tests are now routinely done
for TGE in pigs and BRSV in cattle.
IPx, however, is available and can be
used for a long list of diseases in
livestock and pets.
Nucleic Acid Hybridization/DNA
Probes: a tiny fragment of the genetic