COVER 1 - NMHBA SUMMER 2017 low res

“In horses,
however, we are
dealing with
antigenic drift,
instead, which
is fortunate. The
equine flu viruses
have minimal
changes in their
coating.”
“The antigens, which are the surface
proteins on the virus, can shift. This is their
way of eluding the immune system and
surviving/perpetuating. Every virus has its
own method,” he explains. Herpes viruses
hide in the body where the immune system
can’t recognize them; these viruses become
latent, and then come out of hiding later
to cause recurring disease, like shingles in
humans, or IBR in cattle.
“Influenza is different. It doesn’t stay in
the body at all. The trick it developed is the
ability to shift its outer coating. Every time
these viruses circulate around the world,
they mutate and change their coat so the
immune system doesn’t recognize them.”
The virus has a new disguise to escape the
body’s immune defenses.
“In humans, the influenza virus does a
frequent antigenic shift, with a new coat or
disguise. This is why every year the CDC
designs a new vaccine that contains what
they think will be the virus strain that will
hit the U.S. They acquire data about viruses
circulating in the Middle East, Far East, Asia
and Europe, and try to determine which
one will come to the U.S. Some years they
don’t do a very good job of guessing which
strain to incorporate in the vaccine. Another
strain comes in and affects a lot of people.
It’s always a bit of a gamble. They do the
best they can, but there’s no guarantee. The
ever-changing coat on the human flu virus is
called antigenic shift,” he explains.
“In horses, however, we are dealing
with antigenic drift, instead, which is
fortunate. The equine flu viruses have
minimal changes in their coating. The two
that you hear of are HA (hemagglutinin)
and NA (neuraminidase). Those are the
two surface proteins we find in equine
influenza, and there are minimal drifts. We
don’t have to change the vaccine (change
the antigens that are present in those
vaccines) every year. But, it is important
to track them. There are several groups,
and we want to see if there are any major
changes in those populations,” he says.
“About 15 years ago, there was a shift
between European and American strains.
These all originated from what we call
the Florida strain and they broke into two
separate groups that are termed Clade 1
and Clade 2. There is evidence that the
Clade 2 strain predominately circulates in
Europe, and the Clade 1 predominately
circulates in the U.S. We’ve had no
outbreaks of Clade 2 in the U.S., but there
were one or two cases found in imported
horses that were picked up in quarantine
stations. There are no reports of a Clade 2
outbreak in the U.S.” says Crisman.
“A research group at the Gluck Center
looked at the Clade 1 strains that we
have here, in our vaccines, to see if they
would protect against the European
strains, and they do. The OIE, which is
the World Health Organization for horses,
is recommending that horses traveling
internationally should be vaccinated with
both the Clade 1 and Clade 2 strain.
But our data here shows that if there is
an outbreak of Clade 2 in the U.S., our
vaccines should help,” he says.
“Influenza is a pesky virus, but we see
more problems with herpes than with
influenza. It’s not
the influenza
virus itself
that is a big
problem; it’s
mainly the
secondary
complications
that can
occur that can
be tragic. This
sequel can happen
if people don’t follow
biosecurity guidelines,
rest guidelines, etc. If
you take care of the horse,
the virus will run its course
and the horse will recover,”
says Crisman.
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