Strangles is an highly contagious respiratory infection of horses that is caused by the bacterium Streptococcus equi (S. equi).
It is one of the oldest known equine infectious diseases and is the most commonly diagnosed equine infectious diseases around the world.
The bacteria accumulate in the throat region of the horse within hours of infection, and then infect the local lymph nodes under the jaw resulting in abscess formation a few days later.
Strangles is rarely fatal, but can cause severe discomfort to cause difficulty eating, and respiratory distress due to large abscesses pushing on the airway. Infection rarely spreads to other parts of the body, yet when this does occur abscesses may form in other organs such as liver, kidney, lungs or spleen. When this happens, it is known as ‘Bastard Strangles’.
The infection may also trigger a hypersensitivity reaction triggering the disease purpura haemorrhagic, which is rare, yet often fatal.
Unfortunately due to the stigma attached to Strangles amongst the wider equine community diagnosis and the required effective control may be hindered, therefore, it is vitally Important to:
- Increase awareness and emphasise importance of early diagnosis and control.
- Improve openness and communication within the equine community. Owners + Vets + Yard Owners.
- Develop a contingency plan for a strangles outbreak.
The disease is characterised by a high temperature (often >39.5°C)
Followed by any of the following symptoms:
- Abscesses in the lymph nodes of the head and neck.
The abscessed lymph nodes may drain externally or into the guttural pouches (blind-end sacs connected to the throat in horses) resulting in nasal discharge;
- Profuse nasal discharge
Transmission of Strangles
The spread of Strangles usually requires direct close contact between infected and susceptible animals or indirect carriers, such as people’s hands/clothing, grooming and yard equipment, communal drinking troughs, of the bacteria from horse to horse.
The incubation period of strangles varies from 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 far longer, up to 3 weeks or more.
Around 10% of horses that recover from strangles become persistently infected with S. equi. These apparently healthy ‘carriers’ harbour the bacteria in congealed bean-sized balls of dried pus called ‘chondroids’. The diagnosis and treatment via endoscopy of carriers is critical to preventing future outbreaks.
A presumptive diagnosis can be made by the vet from the horses clinical presentation.
To confirm diagnosis, the bacteria has to be identified using other techniques:
- Taking a Nasopharyngeal swab for culture (grown) in a lab and identification. Yet animals carrying the bacteria can be difficult to detect using the culture test and negative results from a single nasopharyngeal swab do not prove that an animal is not infected. However, three consecutive negative swabs over a 2-week period tested for culture and PCR will provide strong evidence that the infection has been eliminated.
- Taking a blood sample for ELISA detecting antibodies the horse has generated against the bacteria. This is used to screen for exposure of the horse to strangles within the last 6 months.
- Guttural pouch Endoscopy. Culture and PCR of lavage samples collected from the guttural pouches on a single occasion is considered the Gold Standard and to have equivalent sensitivity to collection of 3 Nasopharyngeal swabs. The diagnosis of carriers can be confirmed by guttural pouch endoscopy where a small camera is passed into the guttural pouch. During this process chondroids can be physically removed from the guttural pouch and antibiotic gel instilled to kill off residual bacteria. Treatment of carriers in this way can be extremely effective and can prevent further outbreaks.
The majority of cases are uncomplicated and only require supportive care (such as soft food, shelter, anti-inflammatories) and drainage of abscesses by the use of hot packing or surgical lancing by the vet.
Antibiotics are not always useful as they cannot penetrate the centre of an abscess where there is no blood supply. However, early treatment with antibiotics may be helpful if lymph nodes have not become enlarged. Each case should be assessed individually.
Control & Prevention
Due to the highly contagious nature of Strangles it is vital to stop further spread of the disease. The ease with which the disease spreads through groups of horses is largely dependent on how an outbreak is managed.
Prevent Direct Transmission
Prevent contact of infected horses with all other horses.
Stop any horses from going on or off the yard, and therefore isolating the infected animals
Identify and segregate into 3 groups to control disease within the herd:
- Infected horses
- Horses who have had close contact with infected horses
- Horses who have had NO contact with infected horses.
Prevent Indirect Transmission
Strict hygiene is essential to minimise the spread of disease to uninfected horses.
Extra care should be taken to ensure that horses which are not infected don’t become infected:
- DO NOT SHARE any of the same equipment (tack, grooming kit, buckets etc..) as those with Strangles.
- PROTECTIVE CLOTHING is worn when dealing with infected horses and is removed before moving between horses.
- HAND WASHING between horses.
- FOOTBATHS containing disinfectant should be placed at the entrance/exit of all areas of infection and used on entrance and exit.
Any infected horses should be dealt with after all uninfected horses.
If the correct protocols are followed with extreme care, it may be possible to resume normal operations on uninfected parts of premises.
Strangles is a very unpleasant and potentially life-threatening disease which causes a great deal of suffering. However, with care, outbreaks can be controlled, and the worst effects avoided.