Vaccinating Against Strangles, Pt. 2 – Know The Facts First

Streptococcus equi, the causative agent of Strangles, is perhaps the most contagious bacterial disease a horse can have. Once exposed to the bacteria, your horse and you are potentially on the way to three weeks of misery. And if S. equi finds its way into the barn, wild fire is the only phrase to illustrate the spread of the disease.Streptococcus equi, the causative agent of Strangles, is perhaps the most contagious bacterial disease a horse can have. Once exposed to the bacteria, your horse and you are potentially on the way to three weeks of misery. And if S. equi finds its way into the barn, wild fire is the only phrase to illustrate the spread of the disease.

Story originally posted by: Katie TimsHorseCity.com Free-Lance Writer

Streptococcus equi, the causative agent of Strangles, is perhaps the most contagious bacterial disease a horse can have. Once exposed to the bacteria, your horse and you are potentially on the way to three weeks of misery. And if S. equi finds its way into the barn, wild fire is the only phrase to illustrate the spread of the disease.

With strangles being that pervasive, most horse owners can’t run fast enough to the vet supply for a bag full of shots. But not so fast – there are a few things you should know before you pop off the needle cap and plunge head long into an inoculation program.

Even if you follow the directions to a tee, vaccinating against strangles does not guarantee your horse won’t contract the disease sometime down the road. "In the case of the exposed, potentially already infected animals, the clinical attack rate should be reduced by 50 percent," notes Dr. John Tuttle DVM, professional services manager at Fort Dodge Animal Health. This means that even if you do vaccinate your horse it still has a half chance of coming down with strangles.

"In the face of an outbreak and potential pre-vaccination exposure, owners should be informed of this so they are not disappointed with the results," he continues. Although it’s not the prefect preventative, properly administered vaccine does appear to lessen the severity and duration of strangles.

With some equine ailments, once the horse is vaccinated against or recovers from the disease, the animal has a formidable natural immunity. That’s just not the case with strangles. "It does not stimulate the horse’s immune system very well," explains Dr. Tuttle. "S. equi is probably one of the most complex behaving organisms there is. "One reason strangles is so tricky is because a protective shell, which keeps it from being destroyed by the horse’s white blood cells, encapsulates the bacteria. Consider it a cloaking device, allowing S. equi to travel freely and safely to its respiratory tract destination.

There are two routes a horse owner can take when vaccinating against strangles. There’s the intra-muscular injection, which is an inactivated whole bacterium. This means the outside shell is intact, but the bacteria are basically dead. "Manufacturers tried to make it as close to the bug as they could so that it would stimulate the horse’s immune system," explains Dr. Tuttle. "Unfortunately by doing that the vaccine ran the risk of increased side effects."

The IM strangles vaccine can be a painful experience – in more ways than one. Not only are there the usual risks inherent with all preventative injections, but inoculated horses might also experience side effects mimicking strangles, including nasal discharge, lethargy, extreme soreness in the neck muscles and even abscesses. Pain in the horse’s neck can be so severe that owners must elevate food and water because the horse will not lower its head to eat and drink. There are steps you can take to help the horse through this period. Ideally, the injection should be given in the hind leg to minimize effects to the neck muscle. Next, the horse should be encouraged to move about the paddock or pasture versus being confined to a stall.

"If a person wants to give the injectable, then I would pre-medicate the horse with Bute or Banamine for a few days prior to and a couple days afterward," Dr.Tuttle suggests.

Along with the IM vaccine, there is the intra-nasal variety that is deposited up into the nose through a four-inch flexible tube. This type goes directly to the source of the problem without taking a detour through the horse’s muscular and vascular system. You see, no matter if S. equi enters the horse’s body through inhalation or ingestion, this nasty bacterium congregates in the head and neck region and sets up headquarters in the guttural pouch, or middle ear. When the vaccine is administered directly to the strangles base camp in the nasal cavity, it produces a powerful localized immunity capable of delivering a knockout punch to the S. equi bacterium.

"In the nasal passage and in the back of the throat there is all sorts of lymphatic tissue which when stimulated do produce antibodies," Dr. Tuttle explains. "What we’re trying to do is get that vaccine deposited to where you can get a localized response." Why does that work? "It stimulates different antibodies," Dr. Tuttle answers. "With the intra-nasal, you’re hitting the upper respiratory system, which includes the trachea, up through the throat and nose. It localizes the antibodies where the disease actually is encountered."

It might also produce fewer repercussions than its intra-muscular counterpart. "There is still the potential with the IN, but not near the incidence," Dr. Tuttle claims. Whereas the injectable vaccine is fairly straightforward in its administration, horse owners should consult an experienced veterinarian with the intra-nasal.

Just like any preventative inoculation, it’s vital to maintain the follow-up regimen. "Once given, it is important that the second booster be given within two to three weeks," Dr.Tuttle advises. "The initial IN dose produces a rapid antibody response, but it’s short lived. The second dose produces a more profound duration of immunity.

"If there is a lapse between the first and second vaccinations, the horse is susceptible to strangles. In fact, if the horse actually contracts the disease and then is given a vaccination, it can experience a serious condition referred to as purpura. The double dose of S. equi via transmission and vaccination can overly stimulate the horse’s immune system, which might accelerate into an irreversible high gear.

"It goes overboard and the antibodies act just like little Pac Men," Dr. Tuttle describes. "Simply put, they are looking for the Strep bacteria but unfortunately they bite through some of the blood vessels and they get to oozing serum through the skin." Purpura is the absolute worst-case scenario. And thank goodness, it’s extremely rare.

Although many horse owners might chose the intra-nasal vaccination over the intra-muscular, the American Association of Equine Practitioners recommends that a combination of the two be given, starting with foals at four to six months of age. Each targets a specific group of antibodies and when administered in tandem, gives your horse the best protection possible. The group suggests that at-risk adult horses be vaccinated one or two times per year. Vaccination protocol should be modified, depending on the horse’s condition, age, use as well as the climate and potential exposure.