Sunday, May 19, 2013

Horse Vaccines

So How Do Vaccines Work?

A horse vaccine contains a harmless form of a disease-causing organism.

When the vaccine is given to a horse it tricks the horse's immune system into believing its body is under attack by the real thing.

This causes the horse's immune system to work to identify what is attacking it, and to figure out what type of antibodies will kill it.

The horse will produce antibodies until it successfully produces the right type of antibody that kills off the "practice" disease provided by the vaccine.

Thanks to this valuable practice, if the horse should ever be exposed to the real disease it will be able to identify it quickly and begin producing large numbers of antibodies to quickly and efficiently kill it.

Do Vaccines Always Work?

Most of the time vaccines do a good job of providing immunity for our horses, but sometimes a horse can get sick anyway. No vaccine is ever a 100% guarantee your horse won't get sick.

If your horse does become ill with a disease he or she has been vaccinated for, the chances are good that the vaccine will at least reduce the symptoms and duration of the illness.

How Long Does A Vaccination Last?

Usually, horse vaccines do not provide a lifetime of immunity. You should consult with an equine veterinarian in your area to know what vaccines to give to your horse, and when or how often to repeat them.

Common Terms Associated With Horse Vaccines and Vaccinations

When talking to your veterinarian and/or buying vaccine it can be confusing to hear the proper terms sometimes used with horse vaccines, or to read them on the package label.

Below is a short list of very common terms used when talking about vaccines:

Adjuvant:  A vaccine adjuvant is something that is mixed with the vaccine to cause a better immune response by the horse's body. Not all vaccines have or need adjuvants. Common adjuvants that come with some vaccines for horses today are Havlogen and Spur.

Antigen:  An antigen is a substance that stimulates the immune system to produce antibodies.

Attenuated:  Attenuated means weakened, thinned, reduced, or diminished. Many vaccines are made from attenuated strains of disease-causing organisms.

Efficacy:  When talking about vaccines, efficacy means the ability to create or produce the desired amount of protection from disease.

Intramuscular Injection (IM):  An intramuscular injection is when medications (including vaccines) are delivered into the muscle by a needle. Many equine vaccines are given by intramuscular injection.

Killed Vaccines (also called inactivated vaccines):  This is a vaccine that contains a disease causing organism that has been killed or inactivated. Killed vaccines are frequently teamed up with an adjuvant (see "adjuvant," above) to help boost the immune response.

Modified Live Vaccines (also called modified-live vaccines or live-attenuated vaccines):  These are vaccines that contain disease producing organisms that are still alive, but they have been modified (see "attenuated," above) so that they don't cause illness.

Pathogen:  A pathogen is any organism that causes disease.

Subcutaneous Injection (SQ):  A subcutaneous injection is when medications (including vaccines) are delivered just underneath the skin by a needle. Some equine vaccines are given by subcutaneous injection.

Virulent:  Virulent means full strength, not weakened, capable of causing illness or disease.

Common Equine Diseases

Tetanus:  Often referred to as “lockjaw”, tetanus is caused by a toxin-producing bacterium that is often found in the soil. It can enter the skin through cuts, wounds or a newborn’s umbilicus.

Symptoms include muscle stiffness and rigidity, flared nostrils, prolapsed third eyelid and legs stiffly held in a sawhorse stance. As the disease progresses, muscles in the jaw and face stiffen, preventing the animal from eating or drinking. More than 80% of affected horses die.

Strangles: A highly contagious, yet rarely fatal, bacterial infection characterized by abscess of the lymphoid tissue of the upper respiratory tract.

Strangles is transmitted through contact with infectious excretions and surfaces containing the resilient bacteria.

Encephalomyelitis: More commonly known as “sleeping sickness”, this virus is transmitted to horses by mosquitoes that have acquired it from birds and rodents.

Eastern (EEE) and Western (WEE) equine encephalomyelitis have been noted in the United States.

Venezuelan (VEE) equine encephalomyelitis has not been seen in the U.S., however a recent outbreak occurred in Mexico.

Symptoms vary, but all result from degeneration of the brain. Early signs include fever, depression and loss of appetite. As it progresses, staggering gait and paralysis may develop. Depending upon the strain, between 20 and 100% of infected horses die.

West Nile Virus:  A virus transmitted by mosquitoes that have acquired it from birds or other animals. West Nile Virus infects the central nervous system, and presents with symptoms similar to Encephalomyelitis.

Although it has been responsible for equine deaths, most infected horses can achieve full or partial recovery with supportive therapy.

• Rabies: The rabies virus is most often transmitted through contact with the saliva of an infected animal.

Rabies affects the central nervous system and leads to cerebral dysfunction, including excess salivation, abnormal behavior and aggression.

Though horses are infected infrequently, it is always fatal. Rabies can be transmitted from horses to humans.

Equine Herpesvirus/Rhinopneumonitis (EHV): Two distinct viruses, equine herpesvirus type 1 (EHV-1) and equine herpesvirus type 4 (EHV-4) cause two different diseases, both of which are known as rhinopneumonitis.

Both types cause respiratory problems that may include fever, lethargy, loss of appetite, nasal discharge and coughing.

EHV-1 may also cause abortion, foal death, neurological signs and paralysis. Rhinopneumonitis is spread by aerosol or direct contact with secretions, instruments or drinking water.

The virus may not present any symptoms in carrier animals. Immune protection for pregnant mares requires vaccination with EHV-1 vaccine specifically labeled for abortion protection.

Influenza: One of the most common respiratory diseases in horses, influenza is highly contagious. The virus can be transmitted by aerosol transmission from horse to horse.

Symptoms are similar to those in a human with a cold, including dry cough, nasal discharge, fever and loss of appetite. Horses that travel or are exposed to other horses are most at risk.

Potomac Horse Fever: An acute enterocolitis caused by ingestion of bacterial spores that may be found in pastures bordering creeks and rivers. Symptoms can include mild colic, fever, diarrhea and abortion.

PHF is a seasonal problem with geographic factors.

How and Where to Inject

Horse Injection Guide

Neck Region: Extreme care necessary to hit safe “triangle” of muscle – neither too high in the neck into the large ligament (ligamentum nuchae), nor too low in the neck close to the cervical vertebrae (neck bones).

Though most frequently used, one must avoid the jugular area.

• Hindleg or Hamstring Region: Easy to reach and large muscle area. Be aware horse may kick.

Chest or Pectoral Region:  Easy to reach. Be aware horse may strike, or possible swelling may make walking difficult.

Gluteal or Hip Region: Easy to reach. Be aware that if a post-injection abscess forms here it is difficult to treat. Not a recommended area.

Step-by-Step Injection Guide

• 1.  Use 20-22 gauge, 1.5-inch needle.

• 2.  Use a new, sterile needle for each dose of vaccine and for each horse.

• 3.  Keep needle sheathed until immediately before use.

• 4.  Disinfect skin with alcohol. Tap skin a few times and thrust needle in quickly, deep into muscle, straight all the way to the hub.

• 5.  Carefully attach syringe to inserted needle. Pull back plunger slightly to insure you are not in blood vessel. Blood will appear if you are. If so, withdraw and try again.

• 6.  After withdrawing needle, massage site for 30 seconds after injection to distribute vaccine and help avoid soreness.

• 7.  Allow horse to rest and get free exercise for 2 to 3 days following vaccination, during which time horse may experience slight soreness and lethargy.

Can Vaccines Have Side Effects?

The short answer is yes. In very rare cases vaccines can cause a severe allergic reaction called anaphylaxis. Anaphylaxis is always very serious and can even lead to death.

Vaccines may also cause reactions at the site of injection ranging from mild stiffness, soreness, and swelling, to abscesses.


As with other health information presented here. Since we are not Veterinarians, we can only hope that the user will take the information in the spirit that it is given - as informational. This information is not intended to replace information attained from a Veterinary.

If you are on a vaccination schedule, do not alter your vaccine regiment - especially if it was setup by your veterinarian or other trained animal health care professional.

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