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New EPM test
(from
Thoroughbred Times)
Martin Furr, D.V.M., Ph.D., chief of medicine at the Marion
duPont Scott Equine Medical Center in Leesburg, Virginia,
presented results of his research into a novel diagnostic tool
for equine protozoal myeloencephalitis (EPM) using an equine
gene chip and biomarkers.
A simple diagnostic blood test for an active EPM infection has
been difficult to develop because horses with casual exposure to
the disease and those that have been vaccinated against EPM also
have antibodies against Sarcocystis neurona, the pathogen that
causes the disease, circulating in their blood. So, blood tests
often produce false positives. Invasive spinal taps to test the
cerebrospinal fluid are required for more accurate results, but,
until now, a definitive diagnosis of EPM only could be obtained
by post-mortem examination.
Affymetrix Inc., a genetic technology company based in Santa
Clara, California, and Genetraks Holdings in Bethesda, Maryland,
collaborated with Furr in producing a computer chip that can be
used to look at a pattern of activity, called gene expression,
in circulating white blood cells that would indicate an active
EPM infection and discern it from casual exposure and response
to EPM vaccination.
Gene expression means that certain genes that react to the
disease begin to express proteins. Identifying those active
genes and how they interact, then linking them to the specific
disease that causes them is called a diagnostic signature. This
technology does not look at DNA; it only looks at genes that are
actively expressing proteins.
"We developed a diagnostic signature for EPM that proved highly
accurate, at least in the acute phase of infection--up to 28
days," Furr said. "We’ll probably be seeing more work being done
with this methodology because it is so strong."
The genomic biomarkers are expected to be able to provide
information on the stage of disease and the prognosis, as well
as a means to monitor the progression of the disease and its
response to treatment. Additionally, Furr hopes it will give
clinicians a means to detect EPM before clinical signs emerge,
enabling them to stop the progression of the disease before it
causes damage to the central nervous system.
"We had an overall specificity of 95% to 98% in classifying
these horses [with laboratory-induced EPM]," Furr said. "There
are studies ongoing looking at diagnostic efficiency of this
technique in naturally occurring cases. We can’t give you a
timeline on when this test may become available, but we hope it
will be in the next few months when a commercially available
test will be in use."
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