8. Strangles

What is the aetiology for strangles?

Strangles, also known as equine distemper, is a **contagious upper respiratory tract infection** caused by ***Streptococcus equi (subsp equi)*** **serogroup E**

What is the epizootiology of strangles?

Age – **5 months to 5 years**

Source of infection – infected horses

Persistency in **pharynx for 8 months and remains a risk of infection**. Possible reinfection in 6 months interval. Maternal Ab protect first months of life for up to 3 months, but this disappears within 5 months and not yet developed own immunity.

What are the hosts of strangles?

all equidae

What is the transmission for strangles?

**direct contact, aerosols**, feed, water, equipment

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* Very contagious disease

What is the pathogenesis of strangles?

Excretion through **nasal discharge**

* Acute rhinitis, pharyngitis, laryngitis, regional purulent lymphadenitis.

Dissemination to other lymph nodes, organs. 

* **Abscess formation especially in the guttural pouch = typical sign**. 

After clinical recovery **purpura haemorrhagica 30-50% mortality** 🡪 no complete recovery just clinical

Initial lesions occur in nose, pharynx, larynx, and lymph nodes, before the pathogen disseminates to other lymph nodes and organs. There is swelling of lymph nodes, causing compression of the respiratory tract, which may lead to strangulation (hence the name).  **After clinical recovery, there is overproduction of certain antibodies against the pathogen**. These antibodies deposit on blood vessel walls and activate a strong immune response. White blood cells accumulate and release enzymes that damage blood vessels. The blood vessels become leaky, which results in haemorrhage and loss of fluid into the tissues.

What is the incubation period of strangles?

1-3 weeks

What are the clinical signs of strangles?

Fever, anorexia, depression, **nasal discharge**. 

Dyspnoea, productive cough, **swallowing difficulties. Enlarged, painful, hot lymph nodes due to acute inflammatory process.** 

Lymphadenitis, purulent nodules, **obstruction oedema of legs**. 

**Guttural Pouch Empyema** – filled with pus, which may be concurrent with classic strangles or follow in the immediate convalescent period.

What are the complications caused by strangles?

Complications – pneumonia, meningitis, peritonitis

* **Laryngeal hemiplegia** – involves paralysis of the throat muscles. It is commonly referred to as roaring. The condition may follow abscessation of cervical lymph nodes. 
* Anaemia due to immune mediated lysis of RBC in convalescent or recovery period

Atypical form – mild fever, anorexia, nasal discharge

Apart from the problem of long-term guttural pouch carriers, recovered horses may shed from their nose and in their saliva for up to 6 weeks following infection. All horses that have been infected with equine strangles should be isolated from other susceptible animals for a **minimum of 6 weeks** following infection.

What is the diagnosis of strangles?

Clinical signs, **bacterial isolation from nasal swabs and pus**, antibody detection by **hemagglutination**

What is the treatment for strangles?

Penicillin, **surgical treatment**

What is the prevention against strangles?

Quarantine, hygiene, isolation of new, **vaccination**