Vaccinating Your Horse - What, When and Where

Do you know what you should be vaccinating your horse against?

There are many diseases across the world that our horses can contract, and thankfully there are some we can vaccinate against. The purpose of the vaccination can be one or more reasons, including preventing the disease occurring or spreading, reducing the symptoms of the disease, reducing the mortality of the disease, reducing the risk of infecting other species, and disease eradication.

Below is the summary of these diseases, their symptoms, and the recommended vaccination protocol. As always, if you have concerns regarding any of these, speak with your veterinarian.


Also Known As: Equine Distemper

A horse with ruptured lymph nodes as a result of strangles

A horse with ruptured lymph nodes as a result of strangles

Cause: Streptococcus equi

Prevalence: Worldwide

Spread: Via contact of the discharge of infected horses as they graze, drink or groom, or contamination from handling the infected horse without proper quarantine measures. Not contagious to humans.

Symptoms: The bacteria infect the lymph nodes near the throat and face in nearly all cases. As the bacteria create pus, an abscess forms and the nodes swell. In some cases, the lymph nodes can obstruct the respiratory tract and obstruct breathing, hence the name strangles. Fever, ocular (eye) and nasal discharge present.

Risk Factors: Horse in contact with other horses, shows and events. It is also possible for some horses to become non-symptomatic carriers (they look healthy but spread the disease).

Initial Vaccination: 3 doses 2 weeks apart.

Repeat Vaccination: Every 6-12 months after initial course.



Also Known As: Lockjaw

Cause: Clostridium tetani

Prevalence: Worldwide

Spread: The bacteria is present in the soil, and contamination occurs after the bacteria enter an open wound.

Symptoms: Initially present as stiffness and reluctance to move, which progresses to muscle spasms, nostril flaring, wide eyes and difficulty chewing. The muscle tremors then spread across the body, resulting in violent jerking movements in response to sudden noises or movements.

Risk Factors: Majority of unvaccinated horses that contract Tetanus will die.

Initial Vaccination: 2 injections 4 weeks apart, then another injection 12 months later.

Repeat Vaccination: Every 1-3 years after initial vaccination course.


Equine Hendra Virus

Cause:  Hendra Henipavirus

Prevalence: Australia

Spread: Bats are listed carriers of Hendra, but it is unknown how the virus transmits to horses. Horses and humans can be infected through contact with respiratory and salivary secretions, urine or faeces of an infected horse.

Symptoms: fever, nasal discharge, difficulty breathing, colic, muscle twitches, difficulty walking and lack of appetite have been noted in horses carrying Hendra. Sudden death after a brief illness can occur also.

Risk Factors: As this is a newly discovered disease, more research is pending on its spread and prevention. It is recommended to keep sick horses quarantined and there has been some discussion about ensuring bats don’t have access to contaminating feed bins and water troughs with faeces or urine. Unfortunately the mortality rate is high for both humans and horses, and there has been some other species which have been exposed to this virus.

Initial Vaccination: 2 vaccinations 3 weeks apart, then a third 6 months later.

Repeat Vaccination: Annually after that. Note: horses that receive the Hendra vaccine in Australia need to be microchipped and recorded on a central registry.



Also Known As: Equine Herpes Virus

Cause: EHV-1 or EHV-4, although there are 5 known EH viruses

Prevalence: Worldwide

Spread: Via inhalation of infected respiratory discharge, or contact with infected aborted foetal material.

Symptoms: respiratory discharge, lethargy, decreased appetite, and spontaneous abortion.

Risk Factors: Horses transported to high risk grounds (showgrounds, racetracks) or horses living with horses that travel.

Initial Vaccination:  2 vaccinations 4 weeks apart, then a booster 6 months later.

Nasal discharge, commonly seen with Herpes or Horse Flu

Nasal discharge, commonly seen with Herpes or Horse Flu

Repeat Vaccination: annually for low risk horses, as frequently as 6 monthly for higher risk horses.


Equine Influenza

Also Known As: Horse Flu

Cause: equine-1 (H7N7) and equine-2 (H3N8). It is thought H272 may be extinct as it hasn’t been recorded in over 2 decades.

Prevalence: Worldwide

Spread: Via infected air

Symptoms: fever, cough, nasal discharge, lethargy and decreased appetite, which can develop into pneumonia.

Risk Factors: This is highly virulent, so exposure to any horse that is infected can shed the virus. There are some horses that can develop immunity but still shed the virus. Horses travelling or interacting with new horses are at higher risk of contracting the disease.

Initial Vaccination: 2 vaccinations 4 weeks apart, then a booster 6 months later.

Repeat Vaccination: annually for low risk horses, as frequently as 6 monthly for higher risk horses.


Potomac Horse Fever

Also Known As: Shasta River Crud, Equine Monocytic Ehrlichiosis

Cause: Neorickettsia risticii

Prevalence: North America

Spread: Accidental ingestion of an insect that has ingested a larval stage of the fluke Neorickettsia risticii. It is not spread from horse to horse, although many horses in the same paddock may be affected.

Symptoms: acute fever, depression, low appetite, mild colic, decrease in defecation, diarrhoea. Abortion or acute laminitis may also occur

Risk Factors: this is a disease that is difficult to prevent, but incorporating particular farm management approaches with the vaccination can reduce the risk of contamination.

Vaccination: Early spring, with a booster early summer, each year.



Cause: a neurotopic virus from the lyssavirus genus

Prevalence: Europe, Asia, Africa, North & South America

Spread: Via contact with infected saliva into an open wound. Often, an infected animal biting is the primary cause.

Symptoms: Horses infected with Rabies show a variety of symptoms but nearly all are neurological, including muscle weakness, trembling, lack of coordination, circling, head pressing, sensitive to touch or sounds, aggression or sudden death.

Risk Factors: Rabies is fatal to all animals, and can be transmitted across many species, including humans.

Initial Vaccination: First vaccination followed by a booster 3-6 weeks later.

Repeat Vaccination: Annually after initial course.

Head pressing, a symptom of neurological problems including viruses

Head pressing, a symptom of neurological problems including viruses



Also Known As: Eastern Equine Encephalitis (or Triple E), Western Equine Encephalitis, Venezualan Equine Encephalitis, Sleeping Sickness

Cause: Viruses from the Alphavirus genus

Prevalence: North and South America

Spread: By mosquitos

Symptoms: fever, anorexia and depression, followed by neurological symptoms.

Risk Factors: The disease has a risk of being spread to other animals including humans via mosquitos. Mortality rate tends to be high, and those that recover will often have neurological damage.

Initial Vaccination: 2 vaccinations 4 weeks apart

Repeat Vaccination: annually, preferably just before ‘mosquito season’


West Nile Virus

Cause: a virus of the Flavivirus genus

Prevalence: North and South America

Spread: via mosquitos

Symptoms: Similar to that of horses with encephalitis.

Risk Factors: Mortality rate is significantly lower, but some animals have been reported to experience ongoing neurological symptoms after recovery.

Initial Vaccination: 2 vaccinations 4 weeks apart.

Repeat Vaccination: annually, preferably just before ‘mosquito season’.


African Horse Sickness

Cause: a virus from the Orbivirus genus

Prevalence: Africa & Middle East. It was also seen in Spain and Portugal in the late 1980’s but has been eradicated with strict cull and vaccination programs.

Spread: via midges and mosquitoes. Some ticks may also transmit the disease.

Symptoms: Fever, cough, respiratory distress, abdominal pain. 2 main forms affect either the respiratory tract of the heart, and the third is often mild.

Risk Factors: Mortality rate in horses is quite high, being nearly 90%. It is lower in other Equids.

Vaccination: Annually, between August – October, where the main vector activity is low.