Bit & Bridle

Equine Strangles Information

Other Names

  • Strangles
  • Distemper (older historical term)

What is Strangles in Horses?

Strangles is one of the most common and contagious infectious diseases affecting horses worldwide. It is caused by the bacterium Streptococcus equi subspecies equi (commonly abbreviated to S. equi) and primarily targets the upper respiratory tract, causing painful abscesses in the lymph nodes of the head and neck. The name “strangles” comes from the strangling effect caused by severe lymph node swelling, which can compress the airway and interfere with breathing and swallowing.

The disease affects horses, ponies, donkeys, and mules of all ages, though younger horses (under 5 years) are most susceptible. Strangles is a notifiable disease in many countries and considered a serious welfare concern. Outbreaks can spread rapidly through yards, competition venues, and livery stables, causing significant disruption and economic loss.

What Causes Strangles in Horses?

Streptococcus equi equi is a highly virulent, gram-positive, beta-haemolytic bacterium. It is shed in large quantities in nasal discharge and pus from ruptured abscesses. The bacteria can survive in the environment — particularly in water sources and on equipment — for weeks to months, making environmental contamination a significant ongoing risk even after infected horses have recovered.

Routes of Transmission

  • Direct nose-to-nose contact: The primary route. An infected horse shedding S. equi can pass it to a healthy horse through close contact at fence lines, shared troughs, or during transport.
  • Contaminated water and feed: Shared water buckets, troughs, and hay nets are common transmission routes. The bacterium can persist in standing water for several weeks.
  • Fomites: Contaminated tack, grooming tools, rugs, clothing, and human hands can carry the bacteria from horse to horse. Flies can also act as mechanical vectors.
  • Carrier horses: This is where strangles becomes particularly insidious. Up to 10% of horses that recover from strangles become asymptomatic carriers, harbouring S. equi in the guttural pouches. These horses show no signs of illness but continue to shed bacteria intermittently and act as a persistent source of infection within a herd.

Signs and Symptoms of Strangles

The incubation period is typically 3–14 days. Clinical signs usually follow a predictable progression:

Early Signs (Days 1–5)

  • Fever (often the earliest sign, typically 39–40°C / 102–104°F)
  • Depression and loss of appetite
  • Nasal discharge — initially clear and watery, becoming thick and mucopurulent
  • Mild swelling around the jaw or throat area
  • Mild cough

Established Disease (Days 5–14)

  • Pronounced swelling and pain in the submandibular and retropharyngeal lymph nodes
  • Difficulty swallowing and opening the mouth
  • Reluctance to lower the head (due to lymph node pain)
  • Extension of the neck to ease breathing
  • Profuse, thick, yellow-green nasal discharge
  • Abscesses forming in the lymph nodes — these ripen and eventually rupture externally, releasing large quantities of pus

Complications

Most horses recover fully, but a small percentage develop serious complications:

  • Bastard strangles: Internal abscess formation in organs such as the lungs, liver, spleen, or brain. This is a life-threatening complication that can occur weeks to months after apparent recovery.
  • Purpura haemorrhagica: An immune-mediated vasculitis triggered by the immune response to S. equi. Horses develop severe, painful oedema (particularly of the limbs and head), skin necrosis, and petechial haemorrhages. Can be fatal.
  • Laminitis: Systemic infection can trigger secondary laminitis.
  • Guttural pouch empyema: Infection within the guttural pouches can result in accumulation of pus and chondroids, requiring endoscopic treatment.

Diagnosis

Clinical signs are often characteristic, but laboratory confirmation is essential for both accurate diagnosis and outbreak management. Diagnostic options include:

  • Bacterial culture: Swabs taken from nasal discharge, ruptured abscesses, or guttural pouch washes can be cultured to confirm S. equi. Culture takes 2–3 days.
  • PCR testing: More sensitive than culture, particularly for detecting carrier animals. Results are typically available within 24–48 hours. PCR of nasopharyngeal swabs or guttural pouch lavage is considered the gold standard for carrier detection.
  • Blood antibody tests (iELISA): Serology measures antibody levels against S. equi. Very high titres suggest recent infection or persistent carrier status and can prompt further investigation. However, vaccinated horses will also have elevated titres.
  • Endoscopy: Visual examination of the guttural pouches by nasopharyngoscopy is essential to identify horses with guttural pouch empyema, chondroids, or ongoing carrier status.

Treatment

Supportive Care

For uncomplicated strangles, supportive care is often sufficient:

  • Rest and isolation from other horses
  • Soft feed if the horse is struggling to swallow
  • Soaked hay, soft grass, or soaked feeds such as sugarbeet pulp
  • Fresh water readily available at all times
  • Hot-packing of external abscesses to encourage them to ripen and burst
  • Once abscesses have burst and are draining freely, keep the area clean and allow continued drainage

Antibiotics

Antibiotic use in strangles is a nuanced topic. In the early febrile phase (before abscess formation), penicillin can halt disease progression and reduce severity. However, once abscesses have formed, antibiotic treatment is controversial — it can interrupt natural immunity development without eliminating the bacteria, potentially leading to atypical presentations or bastard strangles. Antibiotics are generally reserved for:

  • Horses with severe systemic illness
  • Horses with bastard strangles or guttural pouch infections
  • Cases of purpura haemorrhagica (in combination with corticosteroids)
  • Young foals or immunocompromised horses

Guttural Pouch Disease

Horses with guttural pouch empyema or chondroids require endoscopic treatment, including guttural pouch lavage and, in cases of chondroids, endoscopic removal under standing sedation.

Biosecurity During an Outbreak

Effective containment is critical. Implement the following immediately if strangles is suspected:

  • Isolate all symptomatic horses: Move to a dedicated isolation area with a 6-metre buffer zone. Ideally use a separate building.
  • Cohort exposed horses: Those in contact with the index case should be monitored twice daily for fever and discharge — do not mix with the general yard population.
  • Restrict horse movements: No horses in or out until all horses have tested negative.
  • Dedicate equipment: Separate water buckets, feed bowls, grooming kit, and mucking-out tools for each group. Do not share.
  • Disinfect thoroughly: Use appropriate disinfectants (chlorhexidine, iodine-based products, or commercial stable disinfectants) on all surfaces and equipment. S. equi is susceptible to most standard equine disinfectants when used correctly.
  • Control human traffic: People moving between groups should change outer clothing, disinfect footwear, and wash hands.
  • Notify your vet and relevant authorities: In the UK, strangles is not legally notifiable but should be reported to your vet immediately. The British Equine Veterinary Association (BEVA) operates a voluntary reporting system.

Prevention and Vaccination

Vaccination against strangles is available in the UK. The most widely used vaccine is Pinnacle I.N., an intranasal modified live vaccine. It is given by intranasal administration as a two-dose primary course, followed by annual boosters.

Vaccination is most appropriate in high-risk horses — those regularly mixing with unknown horses, attending competitions, or living in large communal yards. It does not guarantee complete protection but reduces disease severity and the risk of outbreaks. Vaccinated horses should not be tested for strangles by serology for at least 6 weeks post-vaccination, as antibody levels will be artificially elevated.

Vaccination is generally not recommended during an active outbreak. Contact your vet for guidance on timing.

Prognosis and Recovery

The vast majority of horses recover fully from uncomplicated strangles within 3–6 weeks. Once all abscesses have ruptured, drained, and healed, and the horse has been clear of fever for at least two weeks, most horses can return to normal management. Before reintroducing a recovered horse to the general yard population, three consecutive negative nasopharyngeal PCR swabs (taken one week apart) are recommended to confirm the horse is not a carrier.

When to Call the Vet

Call your vet immediately if you notice:

  • Unexplained fever in any horse (temperature above 38.5°C)
  • Nasal discharge combined with swollen lymph nodes under the jaw
  • Difficulty breathing or swallowing
  • Multiple horses falling ill in quick succession
  • Severe limb or body oedema in a horse that has recently recovered from a respiratory illness
  • Any suspected strangles on a competition or sales yard

Frequently Asked Questions About Strangles in Horses

How long is a horse with strangles contagious?

Horses with active strangles are contagious from the onset of clinical signs until at least three weeks after the last abscess has healed. Carrier horses may remain infectious for months or years. This is why three clear nasopharyngeal PCR swabs taken one week apart are the recommended standard before returning a recovered horse to the general population.

Can horses be vaccinated against strangles?

Yes. The intranasal modified live vaccine (Pinnacle I.N.) is available in the UK and Europe. It is not part of the core vaccination programme but is recommended for high-risk horses. It reduces severity and spread but does not offer complete protection. Discuss with your vet whether vaccination is appropriate for your horse’s circumstances.

Can humans catch strangles from horses?

Streptococcus equi equi is primarily a horse pathogen. There have been extremely rare documented cases of humans developing lymphadenitis after close contact with infected material, but transmission to humans is considered very uncommon. Standard hygiene precautions (hand washing, avoiding contact with pus and nasal discharge) are sufficient for most handlers.

What is the difference between strangles and bastard strangles?

Classic strangles involves abscess formation in the lymph nodes of the head and neck. Bastard strangles occurs when the bacteria spread internally, forming abscesses in organs such as the lungs, liver, spleen, abdomen, or brain. Bastard strangles is far more serious, often develops weeks after apparent recovery, and carries a significantly worse prognosis. Signs can include weight loss, intermittent fever, colic, and respiratory difficulties — symptoms that are easily attributed to other conditions.