The Case For Vaccination

It was like no colic I had ever seen.  The foal ambled about the bay mare’s side, poking occasionally at his unresponsive dam’s udder.  The mare, though trembling, standing camped out, and sweating, didn’t shift away from her foal or kick at her belly.  She didn’t do anything.  Her vitals didn’t match her symptoms – her heart-rate was sky-high, yet her gums didn’t look that bad, and she wasn’t trying to drop or roll.  As I took her temperature, the tail gave me the clue.  It was cocked out behind her, almost rigid.  Stepping back, her camped out stance, rigid muscles, and tail position clicked together in my head.  I’d seen it in goats and cattle, but never in a horse.  I double-checked her eyes.  Sure enough, the third eyelid protruded slightly.  I felt sick to my stomach – tetanus.

Tetanus was one of those diseases whose signs I learned in vet school but never expected to see in a horse.  Horses had been routinely vaccinated against tetanus for decades; it was simply a part of routine maintenance.  However, the commonplace nature of vaccines in society has, in its own way, put the act of vaccination at risk.

Once upon a time, vaccination was a novel, almost miraculous way to prevent disease.  With the discovery of human vaccines against diseases such as smallpox, polio, and measles, the shadow of childhood mortality faded dramatically.  Yet, as the generations go on, fewer and fewer people remember the very real threat posed by the diseases against which we now vaccinate.  And now, in human medicine, we risk coming full circle.  Parents, confused and alarmed by conflicting news reports or overwhelmed by the numerous vaccination recommendations, are beginning to choose not to allow their children to be immunized.  Unfortunately, in immunology, there is a phenomenon called herd-immunity.  Simply put, the fewer members of a group that are immune to a disease, the greater exposure faced by the group as a whole.  Immunity conferred through vaccination or exposure isn’t an all-or-nothing proposition.  It exists on a spectrum and can be overwhelmed by excessive exposure.  When exposure overwhelms immunity, we get disease.

What do human vaccinations have to do with horses?  Simple – humans make medical decisions for our horses, and our attitudes toward medical technology influence the care of our horses.  Over the decade I spent in equine practice, I noticed a shift in client approaches toward vaccination.  On one hand, many of my clients were better informed about available vaccines than ever.  On the other hand, clients were bombarded with conflicting and often erroneous information regarding vaccination.  Terrified by stories from message boards regarding serious vaccination reactions (rare) or abortions in mares (actually fairly common, and not linked by any evidence to vaccination), clients would often choose to do nothing – accepting the very real risk of disease rather than face the feared (and statistically unlikely) risks of an adverse outcome.

The information age has produced another side-effect.  Our media cycles are now so fast and intense that they are more like media-tornadoes, sweeping away everything but the issue of the moment.  When West Nile virus hit the West Coast in 2004, I began to hear a sentiment that was completely unexpected and weirdly persistent.  “Just give him the West Nile vaccine, Doc.  He doesn’t go anywhere, so he doesn’t need anything else, but I don’t want him to get that West Nile.”  These clients were up to date on the need for West Nile Virus vaccination, but somehow, in the space of a year, they had forgotten the purpose behind any of their horses’ other yearly shots.  I felt like a broken record explaining over and over that mosquitoes not only carried the dreaded West Nile Virus but also the viruses that cause Eastern and Western Equine Encephalomyelitis.

A funny thing had happened.  Horse owners had vaccinated for so long against “Sleeping Sickness” and tetanus with their yearly “3-ways” that it had been decades since most of them had seen cases of these diseases.  The horse community had forgotten why it was vaccinating.

We vaccinate to prevent disease.  Vaccines help an animal to develop the antibodies that will fight a disease-causing agent (pathogen) within the body.  Vaccines are not a smart bomb designed to wipe-out a disease in the environment. Over time, if a large enough percentage of the host population becomes immune and the pathogen does not evolve to develop an end-run around this immunity, a disease may become eradicated as was the case with smallpox.  However, since immunity is not 100% and since many pathogens hide in intermediary carriers such as snails, mosquitoes, and birds, vaccination of one population may not eliminate the disease.

In other words, just because we don’t see it that doesn’t mean it isn’t out there.  Vaccine technology is developing rapidly, and there is a wide array of vaccine products available for horses.  Please, talk with your veterinarian.  Find out what vaccines your horse needs and why.  The mare in the first paragraph had never been vaccinated against tetanus.  As I euthanized her, two thoughts passed through my head: 1) How senseless it was for her to die of something a $10 shot could have prevented, and 2) Her foal hadn’t gotten any tetanus antibody from her, and was now at high risk for the same disease.

Keeping a horse healthy is complicated enough even under ideal circumstances.  Let’s not lose horses to preventable disease.