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Routine Vaccination in Horses – Tetanus and Strangles

Equine vaccinations are a crucial component of any equine health program. They allow us to protect our horses against infectious diseases that can cause severe illness and/or death in the individual.

You may find that recommendations for routine vaccines differ from area to area and between veterinarians. This is often a result of disease prevalence and risk. Your veterinarian is the best person to advise you on the appropriate course of vaccination for your horse.

In deciding what vaccinations your horse needs, your vet will assess:

  • Exposure risk (weather; where you live; age, use and sex of your horse)
  • Potential risk of adverse reactions (eg does your horse have concurrent disease such as Cushings?)
  • Severity and consequence of the disease (is there potential for the disease to infect humans? eg. Hendra virus)

In saying this there are two routine vaccinations that your vet may advise you to give to your horses – Tetanus and Strangles.

Tetanus Vaccination

Tetanus is a disease caused by the bacterium Colstridium tetani.

Bacterial spores that cause tetanus are found in soil, dust and animal faeces and can live for many years as they are highly resistant to heat and dryness.

Tetanus spores enter the bloodstream via any break in the skin caused by wounds, surgical procedures or erupting teeth.

These spores produce a neurotoxin that affects skeletal muscles, resulting in rigidity and spasm. It is an extremely serious disease that without early treatment, will likely result in an agonising death.

It may take some time from inoculation of the body with the tetanus spores until the toxin produces the infection. However, once the toxin is produced, the course of clinical signs is rapid and progressive.

Signs Of Tetanus

The initial clinical signs of tetanus can be very vague. It may appear as if the horse has colic or perhaps has tied up. The horse may be showing signs of lameness, particularly if the initial injury is hoof-related. Sometimes the horse is not eating or dropping food from their mouth. They may be unable to chew.

Within hours you will see muscle stiffness progressing to generalised muscle spasticity. Often horses will stand with their legs outstretched in the ‘sawhorse’ stance.

Other signs include prolapse of the third eyelid, a ‘grimacing’ look where the lips are pulled back and nostrils are flared. The ears are rotated down and backward. Often the tail base is raised and you may notice an increase in breathing effort.

As the disease progresses, any loud noise or startling due to movement or touch will evoke clinical signs of advanced muscle rigidity, third eyelid prolapse, rolling back of the eye and the horse may fall over. Horses that are down often lie with their legs rigidly outstretched, unable to be bent. Their head and neck is often extended upward. The muscles of the diaphragm involved in breathing are usually the last to be affected. Paralysis of these muscles leaves the horse unable to breathe and the horse will die from respiratory failure.

Prevention Of Tetanus

Thankfully there is a vaccine that protects against equine tetanus. While no vaccine is ever completely fail-safe, this vaccine has a high success rate.

All horses with an unknown vaccination history require an initial vaccination, followed by a booster a month later to protect against tetanus. Foals are given vaccine protection at birth (Tetanus Anti-Toxin) and then receive a course of vaccinations starting from 3 months of age.

Depending on the type of vaccination protocol your veterinarian choses, booster vaccinations may be yearly or every five years. Please discuss with your veterinarian to decide what vaccination protocol is right for your horse.

Strangles Vaccination

Strangles is a highly contagious and infectious disease caused by the bacterium Streptococcus equi that affects the lymph nodes of the upper respiratory tract of horses.

Transmission of S.equi is either due to direct contact from horse to horse, or from contact with fomites (property, equipment, clothing etc) that have been contaminated with infectious pus secretions.

Some horses are deemed carriers of S.equi. This means that they can carry the disease without becoming ill themselves, but spread it to susceptible horses. S.equi does not survive for more than 6–8 weeks in the environment.

Strangles most commonly occurs in younger horses (weanlings and yearlings) however, there are no age restrictions. Senior horses and those with concurrent disease or those that have not been vaccinated are at greater risk of infection and re-infection.

Signs of Strangles Infection

Horses infected with Strangles often have a high temperature (greater than 39.5°C) and are dull/depressed and off their food. They may have a clear, watery nasal discharge that soon develops into a thick, yellow pus.

There is often swelling of the lymph nodes and glands under the jaw and in the throat latch region. As the disease progresses, these lymph nodes and glands enlarge, become abscessed and rupture. In severe cases, the horse may have difficulty swallowing and breathing.

Prevention Of Strangles

It is recommended to vaccinate horses that travel and/or frequently have contact with horses from different areas.

For horses that have never been vaccinated against Strangles, or who are well overdue for vaccination, the vaccine protocol is a course of three vaccines, each given two weeks apart. It is recommended that a booster vaccination is given at least every 12 months, and every six months in horses that travel and/or contact other horses regularly.

Many veterinarians will combine vaccination of Strangles with Tetanus vaccination with a single ‘2 in 1’ vaccine.

The protocol when using a ‘2 in 1’ vaccine for unvaccinated horses, or those whose vaccination status is unknown, is a course of three injections, each given two weeks apart:

  1. First injection - ‘2 in 1’ vaccine
  2. Second injection - Strangles only vaccine two weeks later
  3. Third injection - ‘2 in 1’ vaccine given two weeks later

Yearly ‘2 in 1’ boosters are required to maintain immunity.

Additional Vaccinations

In QLD and some areas of NSW, it is highly recommended that you vaccinate your horse against the important zoonotic disease caused by Hendra virus. A horse can contract Hendra virus directly via sniffing or eating matter recently contaminated with flying fox urine, saliva or birth products. An infected horse can also spread infection to other horses (and humans) via body fluids and nasal secretions.

Source: https://www.abc.net.au/news/2011-09-12/hendra-virus-explained/2881140?nw=0&r=Map

Hendra virus infection in horses is often difficult to recognise due to a wide range of clinical presenting signs that can mimic other conditions. Initial signs noticed often include a mild nasal discharge or fever and colic-like symptoms. As the disease progresses, the horse will often have difficulty breathing and show weakness with neurological signs such as an uncoordinated gait and muscle twitching that quickly progresses to recumbency and death.

Previously unvaccinated horses require two initial vaccinations given 3 to 6 weeks apart, followed by a booster 6 months later. All horses who have received the initial three vaccine protocol then require yearly boosters.

It is also recommended that breeding stock are vaccinated. To learn more about what vaccines mares and foals require, check out our article Routine Vaccinations Of Breeding Horses.

About the author

Dr Leigh Davidson BVSc, BApplSc

Director at Your Vet Online

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