Does my horse need to be vaccinated for strangles?
This is question we’re asked pretty frequently, especially since strangles hasn’t been common in our area in the past. Unfortunately, with the rise of “feedlot” brokers and lack of quarantine procedures at most barns, we’re starting to see more of this frustrating disease!
For a refresher on the disease, visit our “frequently asked questions about strangles” page!
So. . . should you vaccinate? This is going to depend on a lot of factors so stay with me!
The main issue with the strangles vaccine itself is that it’s not 100% safe (though, to be honest, is anything ever 100% safe?), and it doesn’t always provide complete protection against the disease.
The major risk of the strangles vaccine is an autoimmune condition called purpura hemorrhagica. This condition causes the horse’s immune system to attack his own blood vessels, a reaction called “vasculitis.” The most common symptom of purpura is swelling of the legs, head, neck, or whole body. This condition is often fatal, due to death of the skin, heart muscle, lung tissue, or GI tract tissue. The good news is that this is RARE, and we can help predict which horses will have this reaction.
Horses at risk for purpura are the ones who have a high titer against the strangles bacteria already. Receiving the vaccine is risky for these horses. Luckily, a simple blood test to measure the titer is available and affordable (around $100 depending on several factors). I recommend a titer prior to considering vaccination for most horses, but older horses (>12) and horses who have had a strangles vaccine in the past are most at risk. Titers are strongly recommended for these horses!
The type of strangles vaccine used makes a big difference in safety and effectiveness as well. There are currently two strangles vaccines available, a killed, “m-protein extract” which is given in the muscle, and a modified live vaccine that’s given intranasally. The intranasal vaccine is more effective and probably safer with regard to risk of purpura. The intramuscular vaccine only reduces disease outbreaks by about 50%, while the intranasal one seems to perform much better (due to the fact that it stimulates immunity right where the bacteria enter the horse- the nostrils!).
There’s one problem with the modified-live intranasal vaccine though, and that’s the risk of forming abscesses at separate injection sites. This means that a horse should, ideally, not receive any other injections (vaccines, joint injections, etc) on the same visit as a strangles vaccine. If a horse receives an intranasal vaccine, then sneezes a cloud of modified live vaccine all over everywhere, a small amount of bacteria could remain on the skin. If a needle then punctures the skin, it can “drag” the bacteria inside and begin abscess formation. The horse won’t get strangles, but the abscess will probably have to be drained in order to heal. Though this complication is also super rare, we usually recommend that horses receive strangles vaccines at a separate visit from their other vaccinations. If a horse needs to get all his vaccines at one time, giving the strangles vaccine AFTER the other injections is the best idea.
Once a horse receives the initial strangles vaccine, he’ll need a booster in three weeks to become completely protected. After that, yearly or twice yearly boosters are recommended based on overall risk of exposure.