3/31/2010 - Vaccination Reactions II

Vet tip of the Day: "Allergic" reactions to vaccination
Key Words: Urticaria, hives, hypersensitivity, anaphylaxis

Most importantly, remember that severe vaccination reactions are rare.  That's why it was difficult to find a decent picture - sorry for the quality of this one.  True hypersensitivity or anaphylactic reactions to vaccines, while rare, do occur and require immediate attention.  The physiology behind these reactions is very complex and poorly understood in horses. 

Anaphylaxis refers to a shock reaction by the body to some foreign substance.  In the case of vaccines, anaphylaxis can occur the first time a vaccine is administered.  An anaphylactic response can vary from mild hives that appear hours after a vaccine is given, to acute life-threatening cardiovascular collapse which can occur within minutes of vaccination.  Epinephrine is the preferrred initial treatment for severe anaphylasis.  It works by counteracting the immediately life-threatening components of the body's severe inflammatory response.  It is usually administered by intramuscular injection.  In the most severe cases, it may be given intravenously.  Administration may be repeated every 15-20  minutes if necessary.

Hypersensitivity and immune-mediated reactions to vaccines also occur and may have similar clinical signs to anaphylaxis.  When these reactions occur, they usually are less dramatic than acute, severe anaphylaxis.  Signs may include swelling of the muzzle, face and throat region, which can lead to respiratory distress, or may manifest as hives, or urticaria.  Depending on the severity and progression of the clinical signs, treatment may include steroidal or non-steroidal (phenylbutazone, flunixin/banamine) anti-inflammtory agents, and/or anti-histamines.

When a horse experiences an adverse reaction to vaccination, the question always arises, should the horse be vaccinated again?  If the reaction is a very sore neck, sometimes changing vaccine brands, and thus the adjuvant used, will help.  If the horse has a true anaphylactic or severe hypersensitivity response to vaccination, the problem is more complex and the decision to repeat vaccination should be made based on the severity of the reaction and consideration of the true risk of the disease against which vaccination is directed.

Finally, for those of you who adminster your own vaccines, be aware that storage conditions are extremely important for vaccines.  Vaccines that are not stored at proper temperatures are significantly more likely to cause adverse reactions than those kept cool at all times. Also, correct administration of intramuscular shots, both with respect to location of the injection and injection technique, play important roles in the safety of injections.  If you choose to vaccinate your own horses, be sure to obtain instruction from a licensed veterinarian or licensed veterinary technician concerning the correct administration of intramuscular injections.  And be sure that your vaccines have been properly stored before you purchase them, check the expiration date, and keep them carefully stored until they are administered.  Better yet, take advantage of the chance to visit with your vet and have a spring wellness check up and make an appointment with your veterinarian to give your spring vaccinations!

It's cold and snowy on March 31 in Northern Nevada.  What's it like where you are?  Looking forward to spring and good riding weather.

03/30/2004 - Vaccination Reactions

Vet tip of the Day: When Vaccinations go Wrong
Key Words: Vaccine, adjuvant, immune system, clostridium

Vaccination season is drawing to a close, but I thought I would return to this subject one more time to talk about vaccination reactions.  Of course I would like to tell you that I have never had a horse demonstrate an adverse response to vaccination, but that would be a big fat lie.  Fortunately, I can tell you that I have never had a horse suffer a serious vaccination reaction that didn't respond promptly to appropriate treatment. There are several types of adverse reactions to vaccination, and it is important that you understand how they differ, both in onset of signs, and seriousness of consequences.


By far the most common adverse reaction to vaccination is the simple sore neck.  I vaccinate hundreds (literally) of horses every spring, and this year to date I know of only two horses which developed significant signs of neck pain following vaccination.  Typically the day after vaccination the owner notices that these horses are unwilling to move their heads, show signs of pain if one of the vaccination sites is touched, and exhibit swelling at the vaccination site.  Occasionally the discomfort will be so severe that horses will not lower their heads to eat or drink, or will pull back if pressure is applied to a lead rope when they are haltered.  Years ago I had a client call to tell me that her horse was having a seizure when in fact the horse's neck was so painful that when the owner tried to lead her forward she reared over backwards in response to the pain.  The vast majority of inflammatory reactions after vaccination resolve within 48 - 72 hours with palliative therapy including warm compresses and phenylbutazone.

This "sore neck" reaction to vaccination is NOT an allergic response to the vaccine.  It is an exagerrated inflammatory response to the ingredient in the vaccine that stimulates the horse's immune system.  This ingredient is called an adjuvant, and is very important in causing vaccines to elicit a strong antibody response by your horse's immune system.  Without this response, the vaccine will not be effective in preventing the disease against which it is directed.  Drug companies spend a lot of time and money developing different adjuvants.  Their goal is to find an adjuvant that is a potent stimulator of the immune system but does not cause severe local soreness.  Over the years I have used many brands of vaccines, and have come to be a staunch supporter of Intervet vaccines.  I believe that their adjuvant causes very few advers reactions, and I have been impressed with the company's dedication to client education and with their committment to research and development of new products to protect horses' health, such as Prevenile, their DNA based West Nile vaccine.

When a horse develops a sore neck after vaccination, it is important to notice whether or not the horse is systemically ill.  Specifically, will the horse refuse food and water even when it is placed so that the horse can reach it without lowering its head? Is the horse's temperature over 102.5 degrees?  Is the swelling at the vaccination site severe and increasing over time?  When the swelling is palpated, is there a crackling feeling underneath the skin?  Does the horse appear markedly depressed?  If the answer to any of these questions is yes, then the horse should be examined by a veterinarian.  As stated earlier, the vast majority of inflammatory reactions after vaccination are not serious and resolve within 48 - 72 hours with palliative therapy including warm compresses and  phenylbutazone.  However, in rare cases, it is possible for a bacteria called Clostridium to grow deep in muscle tissue at a vaccination site. If this unlikely event does occur, it can be life-threatening.
Clostridial bacteria exist normally in the environment in a spore form which can only grow in the abscence of oxygen.  Even when a clean needle and syringe are used and the vaccination is administered correctly, it is possible for Clostridial spore sitting on the skin to be carried deep into the muscle tissue by the needle during vaccination.  When this happens it is a random, extremely unlucky event, and does not mean that the vaccine was administered improperly.  Clostridial infections can be life threatening and require prompt and aggressive treatment. The Clostridium bacteria grow rapidly in the abscence of oxygen and produce several toxins which invade the horse's blood stream and cause severe systemic illness which can be fatal. Therefore, it is always a good idea to contact your veterinarian if your horse has an adverse reaction to a vaccine and discuss your horse's specific clinical signs so that you and your vet can decide if your horse needs to be examined.  If you take your horse's temperature and do a physical examination (see blog on this!) and carefully observe your horse's behavior before you call your vet you will be best able to provide important information in making that decision.

In tomorrow's Vet tip of the Day I will discuss Allergic reactions to vaccination and the importance of careful storage and administration of  vaccines, for those of you who vaccinate your own horses.

Until then,

I believe that education is the key to evolution.
I believe that animals are the key to compassion.
I believe the learning never stops.

2/16/10 All Vaccines are Not Equal

Vet Tip of the Day: How Vaccines Vary
Key Words: Antibody, Cell Mediated, Immune System, Virus, Bacteria, West Nile, DNA

We've looked at the factors that help you decide whether or not to vaccinate your horse against a certain disease.  Now let's examine how vaccines work.

All vaccines work by stimulating the immune system in some fashion.  We think most simply of a vaccine as something that stimulates the production of antibodies.  These antibodies then prevent invasion by either a bacterial or viral disease causing organism.  In fact, there are many different classes of antibodies in the equine immune system, and certain classes of antibody are more effective than others in fighting particular diseases.  For instance, IgA antibodies are very effective in fighting off infections that begin in the upper respiratory tract, such as Strangles.  Therefore, the intranasal Strangles vaccine was designed to stimulate a strong protective IgA reponse.  It does this by physically depositing live, chemically altered Strep Equi bacteria onto the back of the horse's pharynx when the vaccine is injected through the nasal passages.  This live bacteria mimics the actual Strangles organism and causes the horse to produce IgA antibodies in the upper airway which then combat the actual Strangles organism when your horse is exposed to it.  The protection is not absolute, and the antibody response to the vaccine is variable.  In addition, because the vaccine contains live, chemically altered organisms, there is a small risk of inducing a vaccine strain case of Strangles in response to the vaccine itself.

In addition to antibody production, the body has is a second, non-antibody dependent arm of the immune system.  It is called cell mediated immunity and is very important in the body's ability to fight viral diseases.  You may have read about the new technologies being used in some of the equine West Nile vaccines.  Instead of using an altered form of the disease causing organism to directly stimulate antibody production, these vaccine use a variety of technologies involving the actual genetic material (DNA) of the disease causing organism.  DNA based vaccines are more effective in stimulating all aspects of the immune system, thereby providing a stronger, more broad based protection against viral organisms, such as West Nile
Virus.  The Intervet DNA chimera vaccine is a fascinating cutting edge product with excellent safety and efficacy against the West Nile Virus.  To learn more about it, Google: Prevenile, Intervet, West Nile.

Finally, while the ideal vaccine will stimulate all arms of the immune system and prime it to rapidly eliminate an invading pathogen, it can only work if the organism causing disease can be consistently identified by the body.  For instance, the West Nile Virus is a very stable, unchanging organism that looks exactly the same to the horse in Massachusetts and the horse in California.  Influenza, on the other hand, is a viral organism that is constantly changing its appearance.  In exactly the same way our human flu produces new strains all the time, equine influenza undergoes small changes in its viral structure that allow it to evade the defenses of horses vaccinated with products produced using older strains of the virus.  So in the case of equine influenza, not only are we dealing with a viral disease, which challenges both the antibody and cell mediated arms of the horse's immune system, but we also are dealing with a disease that frequently alters its appearance, thereby posing one of the greatest challenges to researchers whose goal is to develop highly effective vaccines.

The subject of vaccines, the immune system, and disease prevention is extremely complex.  Luckily, those diseases which our horses may contract which are most deadly, are also the diseases against which it is possible to develop excellent, safe, and effective vaccines.  The prime examples of these are Tetanus and West Nile Virus.  Therefore, these are diseases against which ALL horses should be vaccinated.

The decision whether or not to vaccinate against influenza, rhinopneumonitis, and Strangles, should be made based on your individual horses risk of disease, and the impact that disease is likely to have on your horse's performance and well-being.  Refer to this past Saturday's blog to review the information that will help you make this decision, and then consult with your veterinarian as well.