Page 34 - NMHBA Summer 2017

“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.”
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.
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 intra- nasally, 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