Horse Disease Prevention – Vaccinations

Another concept I apply to vaccinations is first to determine if you have an open or a closed herd.  A closed one is where the horses go nowhere beyond the boundaries of the farm and no strange horse comes in.  Leaving for a horse show or a hospital visit or a clinic is the definition of an open herd.  Adding new horses or boarding at a boarding barn where horses come and go is also an open herd.  Closed herds need vaccinations against diseases found on the farm such as tetanus and rabies.  Potomac horse fever (PHF) and the encephalitis diseases transmitted by mosquitoes can be considered on closed farms.  So can botulism and anthrax.  But closed farms do not need to consider strangles, flu or rhino.

In horses, the diseases to absolutely vaccinate for are the deadly diseases tetanus and rabies.  Worth considering in this group are the encephalitis diseases of EEE (Eastern Equine Encephalitis), WEE (Western EE), VEE (Venezualan EE) and West Nile Virus (WNV).  All of these can kill with tetanus and rabies being everywhere.  Additionally if your horse contracts rabies he can give it to you and you will die.  Only 1 person on record has survived rabies.  I personally have been attacked by a rabid horse and went through the post exposure protocol.  Vaccinate every horse you have for rabies and do not argue this with me.  I have only seen one horse die of tetanus and there is no reason to not vaccinate your horses for this.  Again, do not argue with me on this.

The encephalitis diseases can kill your horse but they only occur during the mosquito season.  Most governments have sentinel birds that are tested daily for this primarily avian disease.  If they detect it they sound the alarm and if it is found in your area, vaccination against this disease is warranted.  The horse is considered a “dead end host” meaning that the virus doesn’t belong in the horse.  It lives in birds but if a mosquito bites an infected bird and then bites a horse they will become very sick and many die.  In humans, the WNV also jumps from birds to horses and also humans so you will definitely hear if WNV is occurring in the human population.

All the other vaccinations for horses will protect in varying degrees but avoiding exposure is a better course.  These include strangles, influenza, equine herpes virus and Potomac Horse Fever (PHF).  Avoiding new horses coming into a group is effective.  Avoiding a common drinking source is effective for strangles. Botulism is endemic in the soil of certain areas and use of a vaccine should be based on the local vet recommendation.  Anthrax is also a local disease so follow your local vet recommendations.

Potomac Horse Fever is a seasonal disease that has spread across America.  Listen to your local vet recommendations and if unvaccinated, know the first signs of this disease and treat with antibiotics.  When this disease first appeared the tell tale sign for me was a horse avoiding his sweet grain but eating the hay as if nothing was wrong. This was before any diarrhea had started and it was also July through September in New York.

Equine Viral Arteritis (EVA) is another vaccination you need to consult your vet before giving.  It is used in breeding stallions but once vaccinated, the EVA test will be positive. Many breeding organizations require a negative EVA test and thus the positive stallion will be excluded.

Current vaccines are made of two parts.  The first part is the antigen which is a piece of the bacteria or virus or a killed or attenuated virus.  This is the part that the innate or cellular response is made from.  You can call these the 1st responders of the immune system and include T-killer cells as well as groups of inflammatory molecules called cytokines.

The second part of a vaccine is the adjuvant which is a compound that intensifies the antigenic response without actually creating the disease.  It stimulates the adaptive or humoral immune system creating the immunoglobulins that will remember the antigen and mount an attack on any future invasion of the antigen.  This is the purpose of a vaccine – to protect the horse from a future attack of a specific disease.

The more lethal a disease is, the better the response of the adaptive immune system to target and destroy the pathogen.  The weaker the disease or the more variants the pathogen has, the poorer the adaptive response to the disease.  Variants in viruses is why there is no vaccine effective for AIDS or hepatitis-C in humans.  Antigenic drift is why vaccines need to be boosted for diseases such as influenza and EHV.  Only time will tell if a vaccine will be effective against a constantly changing SARS-CoV2 (COVID-19).

A nano-vaccine is being tried for the first time in humans against the new disease called COVID-19.  Here the adjuvant is being eliminated as more but smaller (nano size) antigens are being used as both the antigen signal and the boosting of the humoral response.  This is why, at the time of writing this, a vaccine for COVID-19 is being so rapidly developed.  It is a new technology that may be more effective and have fewer side effects that worry so many against using vaccines.

Vaccination reactions including stiff necks and fever are common after injection.  Many vaccines are now being given intranasally which makes sense for any virus that invades the upper airway.  In SARS-CoV1, the virus only inhabited the upper airways.  This is why this coronavirus was not as worrisome and was quickly eliminated.  However SARS CoV2 inhabits both the upper and lower airways and can have a more devastating effect on the respiratory tract.  An intranasal vaccine may not be effective for this disease.

When I practiced and administered intramuscular vaccine injections I rarely had sore necks or horses with fevers.  I attribute this to shaking the vial like crazy then drawing up 3 ml of the vaccine and then injecting it back into the vial repeatedly until all the settled sediment in the bottom corners of the vial were emulsified.  I then drew up the required dose and immediately injected it into the muscle.  If more than a minute had passed from drawing it into the syringe I once again drew air into the syringe and shook it like mad, expressed the air and injected.  If a vaccine came preloaded into a syringe (not from a multidose vial) I would also draw up air and shake until no more sediment was seen.  Then I would express the air and inject the vaccine.  Injection reactions were so rare that I cannot remember any.

Another tip I would offer is to always give a vaccine for an “R” disease such as Rabies or Rhino on the Right side of the neck.  This way if there is a reaction you know which one caused it.

Another tip is to avoid the vaccines with multiple diseases in one.  Unfortunately it is hard to find vaccines with just tetanus alone so I found that one vaccine with tetanus combined with the encephalitis diseases (EEE, VEE, WEE, WNV) all in one is OK.  Just shake.  ALWAYS give rabies as a separate vaccine and never combined with others.  It is too important a disease with horrible consequences for both you and your horse.

I never give more than 2 vaccinations at a time each with the minimal amount of diseases in the syringe.  Giving too many diseases at once I feel overwhelms the immune system.  I know this requires multiple visits from the vet or better record keeping on your part but giving tetanus, rabies, EEE, WEE, WNV, flu,rhino and PHF all at once is unreasonable.  One of the driving forces behind multiple disease vaccines is the sale of them to veterinarians.  Every spring I was approached by a vaccine manufacturer with offers to purchase their new multi-disease vaccine and if I bought so many units the price would drop substantially or free goods were added worth thousands of dollars and all with delayed billing so I could have vaccination specials to develop income to pay for it all.  Marketing before the health of the horses is what I would tell them.  The truth be told here.

The bottom line here for horse vaccinations is to do them for diseases that will kill your horse, do them judiciously if you need protection (open versus closed herds), avoid diseases by quarantining new arrivals and shake the vaccine like crazy before injecting them.

Vaccinations in horses – Part 2

Vaccinations in horses – Part 3

Podcasts

• Vaccinations For Horses– The Horse’s Advocate Podcast #016 (June 30, 2021)

• Vaccinations For Horses– The Horse’s Advocate Podcast #016 (June 30, 2021)