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  • Strangles- what you need to know!

    Posted on by Abii Dowdy

    What is strangles?

    Strangles is the most commonly diagnosed equine infectious disease in the world. It is a highly contagious bacterial infection of the respiratory tract caused Streptococcus equi var equi.

    The bacteria cause large abscesses, usually around the throat, which can restrict breathing and swallowing. Rarely (10%) horses develop serious complications, including abscesses in the brain and abdomen, known as ‘bastard strangles’ which can be fatal. This is more common in horses that are already immunocompromised e.g. elderly horses, youngsters

    Transmission can be through direct contact between infected and susceptible animals, or indirect contact through sharing tack, water sources, feed buckets etc.

    The incubation period of strangles is 7 to 14 days. However, because infected horses can shed the bacterium for long periods, the interval between new cases in an outbreak can be up to 3 weeks or more.

     

    Signs of strangles

    In most cases horses only show some of the mentioned clinical signs. Most horses mount a strong immune response and the infection resolves within 3-6 weeks.

    • Pyrexia (rectal temperature over 38.5 ?C)
    • Depression
    • Thick, yellow nasal discharge
    • Anorexia & difficulty swallowing
    • Soft, moist cough
    • Lymph node enlargement – in rare cases enlargement can cause partial obstruction of airway, hence where the name ‘Strangles’ comes from
    • Lymph node abcessation, which normally rupture within 10-14 days

    Diagnosis

    A diagnosis of Strangles is confirmed by bacterial culture of the organism or detecting DNA of the Strangles bacteria from nasopharyngeal swabs and/or guttural pouch washes. A blood test can be performed to detect the horse’s antibody response to Strangles, but this will give a false negative result is exposure has occurred recently; two negative results, obtained two weeks apart, are required to confirm a negative diagnosis.

    Treatment

    The mainstay of treatment is non-steroidal anti-inflammatories such as bute, danilon or metacam, which brings the horse’s temperature down and improves appetite and demeanour. The use of antibiotics is contentious and may increase the risk of Bastard Strangles developing, but these are sometimes used if the diagnosis is made early enough. The lancing of abscesses may be required in certain circumstances to increase the speed of clinical resolution. Carrier animals may require infusion of antibiotics directly into the guttural pouches.

    Management of an outbreak

    Management should be tailored to each individual yard. Due to the stigma attached to the disease many people want to keep a diagnosis of Strangles quiet, but this doesn’t help in managing the spread of the disease! Clinical cases should be isolated and movement restriction of horses on and off the premises should be enforced, along with strict hygiene measures.

    A traffic light system is often implemented:

    • Red: infected horses and those displaying symptoms
    • Amber: horses that have been in direct or close contact with those in the red group
    • Green: horses that have not been exposed to infected or in contact horses

    Nasopharyngeal swabs and guttural pouch washes should be used as tools to determine when horses can be moved out of the red group. A single negative guttural pouch wash or three consecutive negative swabs taken at weekly intervals are required for a horse to move out of the red group and be given the ‘all clear’.

    All horses in the amber group should have their rectal temperature measured twice daily; any significant rise in rectal temperature should be treated with suspicion and the horse should be moved to the red group. If horses in the amber group have not shown signs for 14 days after exposure, they can move to the green group.

    The carrier horse

    Up to 10% of all horses that have had Strangles can become carriers. This means they continue to shed the bacterium Streptococcus equi after clinical signs have resolved and can be a source of infection to other horses for several years. Shedding occurs during times of stress, such as after transporting, moving yards etc. This is one of the reasons pre-movement Strangles blood tests are often required by livery yards.

    Why?

    Rupture of the retropharyngeal lymph node abscesses into the guttural pouch can result in thickened pus permanently residing there.

    A single nasopharyngeal swab may fail to identify a carrier horse, so it is advised by the Horserace Betting Levy Board (HBLB) that a series of 3 swabs are taken one week apart. Alternatively, a one-off guttural pouch wash can be performed.

    The endoscopic examination and the culture and PCR of guttural pouch washes is a more definitive way of identifying a carrier horse. Saline is flushed through the guttural pouches, collected and sent to an external laboratory for analysis. If the guttural pouch wash is positive, antibiotics can be instilled directly into the pouch or solidified chunks of pus can be removed.