COVER 1 - NMHBA SUMMER 2017 low res

There are three different types of equine influenza
vaccine available: 1) an inactive or killed vaccine,
given intramuscular, 2) a modified live virus (MLV),
administered intra-nasally, and 3) an inactive/killed
canary pox vaccine, a slightly different category that runs
in concert with the flu virus antigen.
“These are
the goals of
vaccination—to
reduce severity of
illness, to reduce
recovery time,
and to reduce
the horse’s ability
to spread the
disease.”
response and creates strong immunity. We
know that those vaccines work very well.
There are several other vaccines that are
moderately immunogenic, such as the
West Nile vaccine. Herpes and influenza
are not, and this why we tell people who
have horses in high risk categories that
they need to vaccinate a minimum of
twice a year, and many will need to be
vaccinated three or four times per year if
you really want to protect that horse. For
these horses, both the influenza and herpes
vaccinations need to be administered at
regular intervals,” he says.
There are three different types of
influenza vaccine available. “One is
inactivated or a killed vaccine, given as
an intramuscular injection. Every vaccine
company offers one of these. There are
also modified live virus (MLV) vaccines,
and currently just one on the market for
horses. It was developed in the early 1990’s
and there are good challenge studies to
show that it gives protection for up to six
months. This one is administered intranasally,
and is the only one approved for
intranasal use. The third type is a canary
pox vaccine, with a different carrier—
that runs in concert with the flu virus
antigen and helps the immune system
mount a response. This one is in a slightly
different category, but is basically still an
inactivated/killed vaccine,” Crisman says.
“One thing that is crucial for any horse
that has never been vaccinated before, is to
start with a two-dose series. If you don’t
give the booster shots, there will be no
immunity. We have a lot of data showing
this. You need to give the priming dose,
and then a few weeks later the booster—
which will stimulate the immune protection
for whatever period of time it lasts. After
the initial booster series, how often you
vaccinate (once, twice, or 3 to 4 times
annually) would depend on the risk and
general environment of the horse,” he says.
No vaccine is 100% effective. “Some
are better than others, but the risk-based
vaccines, like equine influenza and equine
herpes, are not the greatest. If your horse
was vaccinated a couple months prior to
exposure, he may still get sick but have
less severe clinical signs. An unprotected
horse may have three days of fever and
your vaccinated horse may only have
one. Vaccination can certainly reduce the
severity of clinical signs and shorten the
convalescent period (maybe one week
instead of three weeks). The other big
thing that vaccination does is reduce the
shedding.” Even if the horse does get sick,
he won’t shed as much virus and won’t
shed it for as long, and might not be as big
a risk to other horses.
“These are the goals of vaccination—
to reduce severity of illness, to reduce
recovery time, and to reduce the horse’s
ability to spread the disease. It’s like an
insurance policy. Some people may not
want to vaccinate, but after working in a
veterinary hospital for decades, I’ve seen
many instances where a $20 vaccine would
have prevented a $2,000 medical expense.”
With this small investment, the horse
wouldn’t have suffered through the illness.
“Ideally we would like to provide
long-term immunity with vaccination,
but influenza doesn’t lend itself to a
vaccine that’s as dependable as the ones
for diseases like tetanus, rabies, or EEE.
Those pathogens lend themselves to good,
solid protection, in comparison. We see
a lot of cases where horses die from EEE
or from West Nile, especially when people
don’t vaccinate. The virus is still out there.
The protection varies between vaccines for
different diseases, but it will still help your
horse,” says Crisman.
Vaccine Strains
Some people ask why the CDC designs
a new influenza vaccine for humans every
year, but not for horses. “This is because
of what is known as antigenic shift and
antigenic drift. These are different in horses
versus humans,” he says.
“All influenza viruses originate from
birds. They are the source of all influenza,
and migratory birds may carry the virus,
spreading it over large areas. The virus
mutates in the birds and may cause
problems when it jumps from birds to
mammals. This is how we got swine flu and
other types of flu—especially in mammals
that are living in close proximity to birds.
The real worry begins when it jumps from
mammals to humans. This is where it
becomes very challenging,” says Crisman.
32 New Mexico Horse Breeder