I developed goosebumps as I listened to an equine owner on the other end of an emergency phone call as she described her horse’s neck as if it was “being devoured by flesh-eating bacteria.” I hustled out to Barb’s barn to find her description strangely accurate as 40% of her mare’s neck was sloughing skin and muscle on her right side. Questions began swirling around in my head. It did not seem likely that Mary had an injury to the affected area as she is a demure and quiet mare. “Has Mary had any antibiotics or vaccines injected on this side recently?” The answer was, “Yes, we just vaccinated about 10 days ago with the usual upper respiratory vaccine and tetanus. “Was a strangles vaccine also given at the same time?” Barb nodded yes. “But it was not injected there; it was given intranasally.”
The intranasal strangles vaccine is a modified live that is meant to be mixed together to activate and sprayed in the nostrils. Strangles is caused by i bacterium in horses. S. equi causes infection and often abscessation in the lymph nodes of the throatlatch region and under the jaw, namely the retropharyngeal and mandibular lymph nodes. The resulting large and painful swellings are often accompanied by a ropey and copious nasal discharge. Horses are fraught with a huge inflammatory response causing high fever, lethargy and anorexia. We clinically see a multitude of breathing and swallowing complications that lead to a symphony of unsettling noises. These horses look and feel terrible.
But what does this have to do with sweet Mary? The destruction on the side of Mary’s neck is certainly not the typical equine strangles infection with swollen lymph nodes and all of the other miserable symptoms that go with it. Mary’s tissue reaction is likely caused by a rare complication from the routine intranasal strangles vaccine that inadvertently caused an injection site abscess. When preparing or delivering the intranasal S. equi vaccine, droplets can be accidently sprayed, sprinkled, blown or snorted onto hands, syringes and needles. Think about a simple sneeze contaminating a set of hands, a quick encouraging pat on the neck of the horse, and a needle taking the particles into the deep muscles. A routine vaccination for the flu or tetanus now becomes the vehicle for the microscopic, vaccine particles to gain entry and start a cascade of inflammatory reactions.
I do believe that Mary’s intranasal vaccine was correctly given in the nares. The events that followed are unclear, but likely, either the injectable vaccination equipment or the skin on her neck was contaminated with minute particles of her strangles vaccine. These microscopic particles caused the overwhelming inflammatory response on the right side of her neck, resulting in serious tissue damage.
To avoid potentially contaminating other horses, vaccines, supplies and administrators, it is advisable to consider adopting risk-lowering techniques and stellar vaccine handling habits. Hopefully, you will never have to deal with a case as dreadful as Mary’s.
- Wear a clean pair of disposable gloves for each horse
- Administer all injectable vaccines before the handling and administration of the intranasal vaccine against S. equi
- Do not pat the neck prior to injectable vaccine administration
- Have a separate person mix and administer the intranasal S. equi vaccine
- Do not comingle freshly vaccinated and unvaccinated horses while gathering
- Consider vaccinating for strangles on a different day (> 2 weeks) following the injectable vaccines
- Weigh the risk versus benefit when selecting the intranasal or injectable strangles vaccine
About the Author
Dr. Colleen Lewis is a 1996 graduate of Kansas State University, College of Veterinary Medicine. Her career has taken her to many places as a practice owner, consultant, embryologist, and mentor. She enjoys mixed animal practice, teaching, traveling, farming and high school sports with her husband, Andrew and their three boys.
