Risk-Based Equine Vaccinations


    Equine vaccination
    your horse can help keep him healthy and in some cases save his life.
    According to the American Association of Equine Practitioners, every
    horse should receive “core vaccinations” against diseases that
    threaten the general horse population—eastern and western equine
    encephalomyelitis, West Nile virus, tetanus and rabies. Click here to take the Horse Health College course on core vaccines.

    vaccinations—“risk-based vaccinations”—protetct against
    diseases that usually affect only certain horses, such as those
    exposed to large numbers of horses at competitions or those traveling
    to an area experiencing a disease outbreak. These diseases include
    anthrax, botulism, equine influenza, equine herpesvirus, equine viral
    arteritis, strangles, rotaviral diarrhea and Potomac horse fever.

    your horse need risk-based vaccinations? That’s a question best
    answered by your veterinarian, who can recommend a vaccination that’s
    best suited to your equine friend’s individual needs.

    rapidly fatal disease, caused by a spore-producing bacteria, affects
    horses as well as other animals and humans. Infection can occur if
    the horse ingests or inhales the spores, or if the spores contaminate
    a wound. Fortunately, anthrax is not widespread, occurring only in
    areas with alkaline soil conditions, which allow the organism to
    survive. Horses pastured in areas known to have a high level of
    anthrax spores in the soil should be vaccinated.

    is caused by powerful toxins produced by Clostridium botulinum
    bacteria, which is also found in the soil. The toxin blocks
    transmission of nerve impulses, which causes progressive weakness,
    paralysis, inability to swallow, and often death. Shaker Foal
    Syndrome and Equine Grass Sickness are examples of two forms of
    botulism that affect horses.


    highly contagious viral disease is one of the most common infectious
    diseases of the equine respiratory tract, especially for horses from
    one to five years old. Although equine influenza is found throughout
    much of the world, epidemiologic findings indicate that infected can
    be evaded by quarantine procedures (for example, isolating
    newly-arrived horses for at least two weeks) and pre-exposure

    influenza is spread by virus-containing droplets dispersed during
    coughing. The signs of infection include a high fever, watery nasal
    discharge and a harsh, dry cough.
    Lethargy, weakness and lack of appetite commonly occur. The clinical
    signs usually last only a few days, but the cough can persist for
    weeks. In mild cases, recovery occurs in about 2 to 3 weeks; in
    severe cases, it can take 6 months. Because the influenza virus
    attacks the lining of the respiratory tract, affected horses may
    develop secondary bacterial infections such as pneumonia and chronic


    herpesvirus type 1 (EHV-1) and type 4 (EHV-4) cause respiratory
    disease ranging from subclinical to severe. Symptoms include fever,
    malaise, lack of appetite, nasal discharge and cough. Infection
    usually occurs in young foals, but also occurs in weanlings,
    yearlings and other young horses, such as those starting training.
    EHV-1 can cause abortion in mares, the birth of weak foals, or a
    paralytic neurologic disease. EHV-1 and EHV-4 are spread via
    secretions of infected coughing horses, by contact (direct and
    indirect) with nasal secretions, and for EHV-1, contact with aborted
    fetuses and associated fluids and tissues. The viruses become dormant
    in most horses, which show no signs of infection or virus shedding
    until they are stressed.

    mature horses have some degree of natural immunity to herpesvirus
    respiratory infection, but they may expose other susceptible horses.
    Unfortunately, the development of natural immunity does not occur
    with repeated exposure to the abortive or neurologic forms of
    herpesvirus infection.

    Viral Arteritis

    viral arteritis doesn’t usually cause life-threatening illness in
    health adult horses, but it can cause abortion in pregnant mares and
    occasionally causes death in young foals. Infected post-pubertal
    colts or stallions usually become persistent carriers. Transmission
    frequently occurs by direct contact with respiratory secretions, as
    well as by venereal transmission by infected breeding stallions. The
    virus can also be spread through contact with contaminated objects.

    viral arteritis infections are often subclinical or even
    asymptomatic. Clinical signs, when present, include fever; lethargy;
    lack of appetite; swelling of the lower limbs, scrotum, prepuce or
    mammary glands; hives; swelling around the eyes; conjunctivitis
    (inflammation of the lining of the eyelids); and a watery or mucoid
    nasal discharge. Abortion frequently occurs in unvaccinated pregnant
    mares. Young foals may develop pneumonia, which can be fatal.

    Horse Fever

    horse fever is caused by Neorickettsia risticii, a bacteria-like
    organism. Originally identified in the eastern United States near the
    Potomac River, it also occurs in other temperate locations, primarily
    between late spring and early fall. Cases tend to occur in areas
    where the disease has been confirmed.

    signs of Potomac horse fever include fever, mild to severe diarrhea,
    laminitis, colic and decreased abdominal sounds. The disease can
    cause fetal infection and abortion in pregnant mares, but this is
    uncommon. The risk of infection is low in foals.


    rotavirus is a significant cause of foal diarrhea, causing more than
    half the cases in some areas. The disease can affect as many as 50
    percent of susceptible foals, but with appropriate veterinary care,
    the death rate is less than 1 percent. Transmission of the virus
    occurs when the foal ingest fecal material. The resultant intestinal
    damage causes maldigestions, malabsorption and diarrhea.

    a mare prior to foaling will markedly increase the foal’s antibody
    titer to rotavirus. Vaccination of a newborn foal has no effect on
    the severity of rotavirus infections.

    highly contagious disease, which commonly affects young horses, is
    caused by the bacteria Streptococcus equi subspecies equi. The
    organism is spread by direct contact or by indirect contact with
    stalls, pastures, grooming equipment, hands, clothing and even
    insects contaminated with nasal discharge or pus from draining lymph

    of strangles include fever; difficulty eating or swallowing; lack of
    appetite; noisy breathing; swollen lymph nodes (with or without
    abscess formation); and thick yellow mucoid nasal discharge. After
    recovery, some horses become carriers and shed the bacteria for
    variable periods of time.

    some horses, exposure to streptococcus antigens via infection or
    vaccination can lead to purpura hemorrhagica, a non-contagious
    disorder caused by an immune-medicated vasculitis (inflammation of
    the blood vessels). Clinical signs include hivs with edema (swelling)
    of the legs, lower abdomen and head; hemorrhages under the skin and
    or mucus membranes (such as those in the mouth), tissue sloughing,
    and swelling of the head, which may limit breathing. Horses with
    purpura hemorrhagica need prompt veterinary care.

    See all course materials.


    1. These sound really nasty. But also, many of the symptoms are so similar. It would be hard to know what is going on without a proper test.

    2. I’m so glad my horse has already had his shots. Plus most of these aren’t around my area. Very happy to learn all this stuff!


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