Page 35 - NMHBA Summer 2017

“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
secondar y
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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