Strangles (equine distemper) is a contagious upper respiratory tract infection of horses and other equines caused by a Gram-positive

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were a ...

, ''

Streptococcus ''Streptococcus'' is a genus of gram-positive ' (plural ) or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. Cell division in streptococci occu ...

equi''. As a result, the lymph nodes swell, compressing the

pharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its ...

, larynx, and

trachea The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends from th ...

, and can cause airway obstruction leading to death, hence the name strangles. Strangles is

enzootic Enzootic is the non-human equivalent of endemic and means, in a broad sense, "belonging to" or "native to", "characteristic of", or "prevalent in" a particular geography, race, field, area, or environment; native to an area or scope. It also has ...

in domesticated horses worldwide. The contagious nature of the infection has at times led to limitations on sporting events.

Signs

Shetland pony with strangles (side view)

A horse with strangles typically develops abscesses in the lymph nodes of the head and neck, causing coughing fits and difficulty swallowing. Clinical signs include

fever Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...

up to 106°F and yellow-coloured

nasal Nasal is an adjective referring to the nose, part of human or animal anatomy. It may also be shorthand for the following uses in combination: * With reference to the human nose: ** Nasal administration, a method of pharmaceutical drug delivery ** ...

discharge from both the nose and eyes. Abscesses may form in other areas of the body, such as the abdomen, lungs, and brain. This is considered a chronic form of strangles called "bastard strangles", which can have serious implications if the abscesses rupture. Horses develop this form of strangles when their immune systems are compromised or if the bacteria rapidly invade the body.

Complications

Possible complications include the horse becoming a chronic carrier of the disease,

asphyxia Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that ca ...

due to enlarged

lymph nodes A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that incl ...

compressing the larynx or windpipe, bastard strangles (spreading to other areas of the body),

pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severi ...

, guttural pouch filled with

pus Pus is an exudate, typically white-yellow, yellow, or yellow-brown, formed at the site of inflammation during bacterial or fungal infection. An accumulation of pus in an enclosed tissue space is known as an abscess, whereas a visible collection ...

, abscesses, purpura haemorrhagica, and

heart disease Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, ...

. The average course of this disease is 23 days.

Cause

The disease is spread by an infected horse when

nasal discharge Rhinorrhea, rhinorrhoea, or informally runny nose is the free discharge of a thin mucus fluid from the nose; it is a common condition. It is a common symptom of allergies (hay fever) or certain viral infections, such as the common cold or COVID-1 ...

or pus from the draining

lymph node A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that inc ...

s contaminate pastures, feed troughs, brushes, bedding, tack, etc.

Prevention

Both intramuscular and intranasal vaccines are available, although their efficacy is rated at no more than 50%. Isolation of new horses for four to six weeks, immediate isolation of infected horses, and disinfection of stalls, water buckets, feed troughs, and other equipment can help prevent the spread of strangles. As with any contagious disease, hand washing is a simple and effective tool.

Treatment

As with many streptococcal infections, beta-lactam antibiotics (e.g

penicillin Penicillins (P, PCN or PEN) are a group of β-lactam antibiotics originally obtained from ''Penicillium'' moulds, principally '' P. chrysogenum'' and '' P. rubens''. Most penicillins in clinical use are synthesised by P. chrysogenum using ...

s) are the most effective treatments, but some authorities are of the opinion that use of antibiotics is contraindicated once abscesses have begun to form, as they predispose to lymphatic spread of the infection (bastard strangles), which has a much higher mortality rate. After an abscess has burst, keeping the wound clean is important. A diluted

povidone-iodine Povidone-iodine (PVP-I), also known as iodopovidone, is an antiseptic used for skin disinfection before and after surgery. It may be used both to disinfect the hands of healthcare providers and the skin of the person they are caring for. It may ...

solution has been used with good results to disinfect the open hole, flushing the inside with a syringe-tipped catheter or with a

teat A teat is the projection from the mammary glands of mammals from which milk flows or is ejected for the purpose of feeding young. In many mammals the teat projects from the udder. The number of teats varies by mammalian species and often corr ...

cannula A cannula (; Latin meaning 'little reed'; plural or ) is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of samples. In simple terms, a cannula can surround the inner or outer surfaces ...

, followed by gentle scrubbing to keep the surrounding area clean. Symptomatic therapy is an alternative treatment, and is where warm packs are used to mature the abscesses so making them less painful and more comfortable for the horse, but once the abscesses have been matured, they must be kept clean to prevent further infections. This treatment for ''S. equi'' only helps reduce pain for the horse rather than curing the infection.

Outcomes

Strangles has an 8.1%

mortality rate Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of d ...

. Mortality is lower in cases without complications than it is in cases of bastard strangles. The disease is very contagious and

morbidity A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that ...

is high. Precautions to limit the spread of the illness are necessary and those affected are normally isolated. An isolation period of 4–6 weeks is usually necessary to ensure that the disease is not still incubating before ending the quarantine.

Epidemiology

Equines of any age may contract the disease, although younger and elderly equines are more susceptible. Young equines may lack immunity to the disease because they have not had prior exposure. Geriatric equines may have a weaker immune system.

References

External links

Strangles information sheetAmerican College of Veterinary Internal Medicine consensus statement on StranglesStrangles in Horses, fact sheet, MSU Extension serviceStrangles in Horses, Merck Vet Manual
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