What You Should Know About Vaccines – But Didn’t Dare to Ask…

By: Dr. Dieter Oberbichler, DVM

It’s that time of year again, the birds are chirping, the grass is sprouting, and dreams of horse showing and trail rid-ing are intoxicating our minds! This also means it’s every vet’s busiest season for Herd Health. And with herd health appointments comes the hot topic of vaccines. What vac-cines do I really need? Is it really necessary to vaccinate? There are a lot of opinions out there, but all I can say is that I’d rather deal with a “dreaded” vaccination over the actual disease we want to prevent!!

The AVMA (American Veterinary Medical Association) defines core vaccinations as those “that protect from diseases that are en-demic to a region, those with potential public health significance, required by law, viru-lent/highly infectious, and/or those posing a risk of severe disease. Core vaccines have clearly demonstrated efficacy and safety, and thus exhibit a high enough level of patient benefit, and low enough level of risk to justify their use in the majority of patients.”


A deadly virus that will kill its host once the central nervous system has been infected. I guess the werewolf legend is based on the behavioural changes this virus causes in the brain of sick animals. Shy, wild animals suddenly appear tame, and seek contact with other animals or humans. If they are bitten by an animal with these symptoms, the virus will be transmit-ted from the saliva into the blood stream of the victim.

In horses, cattle, sheep, and other herbivores, rabies does not usually produce the classic “CUJO like” signs, with salivation and aggression, they initially often just appear list-less, off-food, with mild neurologic symptoms like “head pressing” and disorientation. The infected animal will die within about 2 weeks of showing symptoms and while the risk to get bitten by a horse is low, the saliva is high-ly infectious. There is no cure for rabies once it reaches the central nervous system – euthanasia is the only solution; health authorities will also need to be involved due to the potential danger to human lives.

We currently have a flare-up of rabies in Ontario and vaccination of domestic animals against rabies is mandatory (with some exceptions).For dogs and cats the vaccination interval can be extended to three years under certain circumstances, however it is NOT SO FOR HORSES – a booster is required every year to maximize protection!

Caused by the bacteria “Clostridium tetani”, tetanus is fatal in most cases. The spores of these bacteria survive for many years in the soil. If these spores get into wounds, the bacteria “re-activates” and produces a very potent neurotoxin, which blocks neurotransmission, resulting in uncontrollable muscle contraction and spasm (tetany).

It is one of those diseases, that if you have seen it once, you will never forget it again. I remember heart-breaking cases of horses that I could not help despite all efforts, and even after referral to university hospitals the chances for survival are slim, and the road to recovery is slow.

Some have asked me: “Why do we have to vaccinate horses yearly, when humans need it only once every 8 to 10 years?” Similar to the 3-years rabies vaccine in dogs and cats, it depends on the individual vaccine and the immune-response it creates in the animal.

There is simply no Tetanus vaccine available that guarantees reliable protection for more than a year in horses. If you ignore that, you are simply rolling the dice!

Both diseases are transmitted via mosquitos, and the viruses cause neurologic symptoms in horses and other animal species. Certain bird populations are the reservoir for these viruses, and the horse is one of the dead end hosts – this means that a sick horse is not a risk for infection of other animals.

The fatality rate for Eastern Encephalitis is be-tween 80% and 90%; and about 30% of all horses that contract the West Nile Virus showing neu-rological symptoms will simply not make it!

In 2015 OMAFRA listed 5 Eastern Encephalitis cases, and 3 West Nile Virus cases. The actual number of affected horses might be higher as not all cases are confirmed by lab work, or even reported.

I am very aware that we can have adverse vaccine reactions and side effects. But preventative administration of the core vaccines is for sure the lesser evil, in my opinion! I emphasize that every owner in the end, has to make the decision for their horse.

Any vaccine can cause allergic reactions, and even anaphylactic shock. Your veterinarian is prepared to deal with these extremely rare occurrences. The most common side effects are muscle soreness and stiff necks. The horse might need to be fed with a hay net, so that it doesn’t have to bend down to the floor. Non-steroidal medication like Phenylbutazone or Banamine should be given for a few days, and then they will absolutely get over it.

Horses with underlying muscle disease can “tie-up”. I see occasional colic, and every now and then a horse spikes a fever. Further complications are swelling at the injection site and abscess formation.

All of these complications are usually non–life threatening, and when properly dealt with are minor compared to the protection vaccines of-fer. Science evolves constantly, so we might find better ways in the future to protect our horses. Vaccination intervals and recommendations might change over time, but for now – in the interest of the horse – yearly vaccinations with the core vaccines are the way to go.

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