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Kohnke's Own Seasonal Alert - Strangles Outbreak

Strangles Sympton

Strangles, caused by the bacterium Streptococcus equi, is a highly contagious infectious disease of the upper respiratory tract and lymph nodes of the head, affecting horses, ponies and donkeys.

This endemic disease, which tends to favour the colder months of the year, is easily recognised through the symptoms it presents. Outbreaks generally follow the mixing of groups of horses or the introduction of new horses from an infected property. The disease is generally more common in younger horses whose clinical symptoms will be more severe due to a lack of immunity; however, horses of any age can become infected.

The Streptococcus equi bacterium spreads from horse to horse through both the oral and nasal route, through coughing, or by eating feed or drinking water which has been contaminated by an infected horse or donkey. Contaminated grooming gear, rugs, feed bins, stable utensils, transport vehicles or handlers not practicing correct biosecurity measures can also spread the infection. Streptococcus equi can also survive long periods of time in the environment.

The incubation period of the disease is usually 1 week, but may be up to three weeks. Typical symptoms of strangles are usually displayed within 3-8 days of infection and are as follows:

  • rapid on-set of high temperature (39.5°C to 40.5°C)
  • loss of appetite
  • symmetrical inflammation of the head and neck glands that will often form into abscesses
  • discharge of thick yellow pus from the nose
  • coughing
  • difficult and painful swallowing

Strangles SymptomThe clinical signs may persist in some horses for days to months, however, in most cases, once the affected lymph nodes have abscessed and drained, recovery is uneventful. Abscesses typically rupture and drain within two weeks and when they do burst, thick yellow puss will be discharged.

Affected horses remain infectious for at least four weeks after clinical signs have disappeared, even though they may appear healthy. However, some horses may harbour residual infection in the guttural pouch, subsequently shedding the bacteria intermittently for months afterwards.
Other, more severe complications from Strangles include:

  • Bastard Strangles – Bacteria can occasionally spread through the body, causing abscesses in the lungs, liver, spleen, kidneys, brain, and lymph nodes. These cases can be fatal.
  • Purpura Haemorrhagica – This condition is not common. It is normally associated with the appearance of red spots on skin and mucous membranes, caused by bleeding from smaller, sub-mucosal blood vessels. Swelling of the limbs and head may also be present. It is generally fatal despite treatment.
  • Chronic Carrier Status - A small number of horses carry Strangles in the guttural pouch for months after they have recovered from the disease. Carrier horses appear healthy, but shed bacteria in nasal discharges and are the source of infection for other susceptible horses.

Swift veterinary diagnosis is important in the control and spread of the disease.
Testing for Strangles is carried out by swabbing the back of the nasal cavity (nasopharyngeal swabs) the swabs are sent to a lab to culture the Streptococcus equi bacteria. Definitive diagnosis of Streptococcus equi may take several days to culture and confirm. To obtain a positive swab, swabs must be taken before any antibacterial treatment is commenced.

Bacterial shedding will usually end rapidly after the horse’s clinical recovery, but can be confirmed by negative culture of nasopharyngeal swabs. However, shedding may be intermittent and the occasional horse can become a long-term carrier. Ponies have been known to carry the infection for up to 15 months and have been confirmed as the source of infection for other horses 8 months after being infected themselves. Therefore, before any infected horse or any horse that has come into contact with an infected horse can be considered free of infection, a series of negative swabs are needed.

Immediate veterinary treatment should be sought in any suspected case of Strangles, and an attempt to control infection and treat the symptoms is essential. The affected horses should be kept isolated for 6 to 8 weeks in order to prevent spread to other horses and stringent biosecurity must be observed when handling infected horses.
In many cases where the disease is displayed with less severe symptoms, the best treatment is good nursing and management.

Keeping the horse comfortable and quiet until the abscesses burst, will enable it to acquire natural immunity and will generally recover without complications. To reduce the elevated temperature and painful swellings, a veterinarian may prescribe non-steroidal anti-inflammatory medication. Antibiotics are not always administered or are useful, as they will not penetrate the centre of an abscess where there is no blood supply. Anti–inflammatory medications may be necessary if the horse is suffering from painful swellings of the lymph nodes and/or a high temperature.

Early treatment with antibiotics may be given in some cases, however, if antibiotics are administered prior to testing, a confirmed diagnosis may not be provided. Treating abscesses once they have burst can be carried out by washing the site with warm water and antiseptic. Complications are uncommon and most horses recover uneventfully.

Handy Hint: Immune system support medications and supplements encourage recovery from illness and injury by supporting and promoting immune function in the body. Kohnkes Own® Activ-8 has a role in normalising the immune system in horses to maintain optimum immunity and assist in the recovery from illness and injury.

Strangles TreatmentControl and Prevention
Infection can be controlled through the isolation of infected horses for 4-8 weeks. The spread of Strangles can be limited by the early detection of ‘shedders’ amongst newly-infected horses on the property. All infected horses and all horses in contact, should be placed under veterinary supervision in strict isolation with the highest possible standards of hygiene.

The disease can easily be spread by careless horse handlers. Strict hygiene and biosecurity is necessary for people handling infected horses. Larger home properties, such as studs or agistment centres, may be able to allocate separate handlers to tend to infected and uninfected groups of horses. If one single person must handle both infected and uninfected horses, treatment and daily care of the uninfected horses should be attended to first. Infection free horses and their in-contacts can be diagnosed by taking three nasopharyngeal swabs over a two week period and culturing the swabs for Streptococcus equi. Three negative swabs provide strong evidence of freedom from infection in the great majority of cases.

All new horses coming onto a property, whether or not the horse has come from an infected area, should be monitored closely for at least two weeks after arrival, and ideally quarantined during that period. Any horse which develops a nasal discharge and has come from an infected area should be isolated and swabbed to exclude the possibility of Strangles.

Horses kept on properties in isolation from other horses are not at risk. However, horses which travel to studs, competitions or camps, visit other properties where horses are kept, or those on agistment with other horses, are at risk and a regular vaccination program for Strangles is highly recommended.

Vaccination for Strangles does not always prevent disease in individual horses. However, it can assist control by reducing the severity and duration of symptoms, as well as the spread of disease in an outbreak. An initial course of 3 injections two weeks apart is necessary with an annual booster vaccination thereafter.

John KohnkeHorses should be vaccinated initially as a foal, and the mare should also be regularly vaccinated during her pregnancy. For optimal protection, it is important that horses are given a full course of vaccinations and receive regular annual boosters. Horses should not be vaccinated while actively infected.

Horses which are in high risk areas or within a 200km radius of an outbreak are strongly advised to be vaccinated immediately.

Copyright by Dr John Kohnke BVSc RDA (above Left)

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