Streptococcal infections

Streptococcal infections play an important role in equine clinics around the world , because they can cause serious illness with variable and often fatal symptoms. There are two pathogenic bacterial species of Streptococcus sp. that play a fundamental role in horses : Streptococcus equi ssp. equi and Streptococcus equi ssp. zooepidemicus.


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  • 1 Pathogenic bacterial species
  • 2 signs
    • 1 Streptococcus equi ssp infection. equi:
    • 2 Streptococcus equi ssp infection. zooepidemicus:
  • 3 Diagnosis
  • 4 Treatment
  • 5 Prevention
  • 6 Source

Pathogenic bacterial species

There are two pathogenic bacterial species of Streptococcus sp. that play a fundamental role in horses :

  • Streptococcus equi ssp. equi.
  • Streptococcus equi ssp. zooepidemicus.

A Streptococcus equi infection causes mumps, which occurs with inflammation of the upper respiratory tract, mucopurulent nasal discharge, and inflammation of the regional lymph nodes. This infection quickly causes an abscess (usually in the submandibular area), which can be small and resolve over time, or it can be very large, open and need specific treatment. Equine mumps is highly contagious; a horse can be a carrier and transmit the infection , even if it does not show any apparent symptoms. This means that if a preventive strategy of reproduction and vaccination is not adopted, aInfection can cause very extensive outbreaks of this disease among horse populations . S. zooepidemicus is also known to cause paralysis in foals (polyarthritis) and sporadic abortions in pregnant mares.


Symptoms may vary for different Streptococcus species :

Streptococcus equi ssp infection. equi:

Equine mumps:

A contagious infection characterized by the formation of abscesses in the lymph nodes that drain the mucosa of the upper respiratory tract.

  • Incubation period: 3-6 days.
  • Often the first symptom is refusal of foodand drink.
  • Feverup to 41 ºC.
  • Catarrhal inflammationof the mucosa of the upper respiratory tract and inflammation of the lymph nodes of the pharynx and the mandibular region, where abscesses form.
  • Mucopurulent runny nose.
  • Infectionof the central nervous system or of the heart in the most severe cases.
  • Course of the disease: approximately two weeks in each individual, although an outbreak in a stud can last for several months.
  • A chronic form known as “false mumps” may appear, with subsequent infectionof other organs in addition to the upper respiratory tract.

Streptococcus equi ssp infection. zooepidemicus:

  • It is the most frequently isolated pathogenic microorganism in diseasesthat affect the respiratory system.
  • It can cause a venereal infectionthat can cause sporadic abortions .

It can cause paralysis in foals (polyarthritis).


Equine mumps can be diagnosed from clinical symptoms, although not all horses will present with the typical swelling of the lymph nodes in the head and neck. In the past the culture of the bacteria was carried out from samples obtained by nasal lavage or with a swab. However, this diagnostic method is not always accurate because there is a possibility that the horse will not kill bacteria in the early stages of infection or that bacteriadie on the way to the lab. The most reliable method is to analyze the DNA of the bacteria, which also allows the differentiation of the two subspecies, S. equi and S. zooepidemicus.


Treatment of the infected horse :

Proper treatment of horses with mumps often depends on the stage and severity of the disease . The opinion of veterinarians on the administration or not of antibiotics is clearly divided. However, most cases of horse mumps require no treatment other than adequate rest, a soft, dry bed, and a good quality, moist, palatable, soft diet while the disease is allowed to run its course. The horse must have easy access to food and water .

Horses with initial clinical symptoms.

During an outbreak, immediate antibiotic treatment of new cases during the initial acute phase of fever and depression can be curative and can prevent abscess formation. The antibiotics are administered for 3 to 5 days. Penicillin is generally considered the antibiotic of choice for the treatment of non-pneumococcal streptococcal disease, although other drugs may be used , depending on their ease of administration or the point of infection .


To stop the spread of Streptococcus equi infections, good hygiene and good management are essential .

Infected horses should be separated from clinically normal horses. Precautions to be taken:

  • Schedule the exercise of infected horses after that of healthy horses, to avoid the possible transmission of bacteria to horses or stables by riders.
  • That no infected horse has access to a starting box or similar device.
  • Avoid direct contact between horses.
  • People who have had contact with horses during exercise should disinfect their hands immediately afterward.

Vaccination has been shown to greatly reduce the incidence of mumps and the severity of symptoms it causes. It is indicated to vaccinate healthy horses (that is, those that do not show clinical symptoms of this or any other disease ) and it is recommended as an essential tool to prevent outbreaks of horse mumps.


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