If you have a busy boarding or show barn, you dread hearing a horse cough or discovering a drippy nose. Both are early warning signs that mean you might be about to watch a respiratory disease spread like wildfire through your barn. These nasty and highly contagious infections, while not deadly as a rule, can stop your barn’s activity in its tracks. And until recently, it seemed there was very little you could do about it.
Sure, there were vaccines available, but their efficacy was questionable. The traditional intramuscular vaccine for strangles (a.k.a. equine distemper), for example, not only has a history of conferring poor immunity, but also tends to produce painful localized reactions at vaccination sites. Though it may lessen the impact and severity of strangles, most veterinarians feel the vaccine won’t prevent a horse from contracting the disease—and many believe that the risk of an injection-site reaction is greater than the risk from strangles itself. As a result of this, the treatment is often not recommended to horse owners or trainers.
Intramuscular vaccinations against influenza (flu or “the snots”) have a checkered track record. The vaccines are generally only effective against a couple of the most prevalent strains of influenza—and since the virus is extremely prone to mutation, treatment doesn’t provide very broad-spectrum protection. Further, drug effectiveness often lasts only weeks, necessitating repeated injections throughout the show season.
But there’s good news. Years of immunological study have finally paid off with a brand-new approach to equine vaccination. Based on the idea that better immunity is conferred by a vaccine administered where the disease naturally takes hold (i.e. in the respiratory tract), researchers unveiled, in 1998, a strangles vaccine that goes straight up the horse’s nose.
“Of 780 horses vaccinated in one trial, none had any adverse reactions of any kind and most tolerated the nasal spray format very well.”
Manufactured by Fort Dodge Laboratories, and marketed as Pinnacle I.N., the pump spray vaccine is made from a “modified live” version of Streptococcus equi (the bacteria which causes strangles). In other words, the bacteria are altered by removing some of the surface proteins, so they’re no longer able to cause disease, but can still trigger an immune response in the horse. The organisms in the vaccine do multiply in the horse and have the potential to cause a very mild local infection or local lymph node swelling, but they can’t revert to a virulent (infectious) format and die off in the environment of the respiratory tract much faster than the unmodified S. equi. An initial nasal dose, followed by a booster two weeks later, is enough to confer immunity to the horse for a year.
Early results for Pinnacle I.N. have been extremely promising. Of 780 horses vaccinated in one trial, none had any adverse reactions of any kind and most tolerated the nasal spray format very well. In another trial, 85 percent of foals who received the intra-nasal treatment showed far milder symptoms of strangles when they were deliberately exposed to the disease as compared with 40 percent of foals who were classified as having developed mild symptoms without the vaccine.
Hot on the heels of Pinnacle I.N.’s release was the launch of an intranasal influenza vaccine, Flu Avert I.N. Introduced by Heska Corporation in November 1999, the new flu spray is also based on the “modified live” approach and claims to provide immunity for at least six months, a significant improvement over previous intramuscular vaccines for influenza.
Chances are we’ll soon see nasal-spray versions of vaccines for other troublesome respiratory diseases, such as equine herpes virus (formerly called rhinopneumonitis) and rotavirus, a major cause of pneumonia in foals. Exactly how much better these vaccines will be is still to be determined, but it's certainly safe to say they’ll be an improvement on the ones currently available. And that’s going to give horsemen a vital edge in the battle against lost time and performance. [sm]
Karen Briggs is an Ontario-based freelance journalist and photographer, a Canadian Equestrian Federation-certified coach, an equine nutritionist and an eventer.