Equine Strangles: Clinical Signs, Diagnosis, and Biosecurity

Strangles is a highly contagious bacterial infection of horses caused by Streptococcus equi subspecies equi. This article explains how the disease spreads, what clinical signs to watch for, how diagnostic testing works, and which biosecurity measures reduce transmission on your farm. The content is written for horse owners, veterinary students, veterinary technicians, and veterinary professionals who need practical guidance for recognizing and managing this disease.

At a Glance

Strangles is one of the most frequently diagnosed infectious diseases of horses worldwide. The bacterium is host-adapted to equids, meaning it does not naturally infect other species. The disease causes significant welfare and economic costs wherever horses are kept. Understanding the basics helps you act quickly when strangles appears on your property.

Understanding the Disease

Strangles has been recognized as an infectious disease of horses for centuries. The causative organism, Streptococcus equi subspecies equi, is closely related to other streptococci that cause disease in horses and other animals. The bacterium is highly adapted to the horse and does not survive well outside the host for extended periods, but it can persist in the environment under the right conditions.

The disease is characterized by inflammation of the upper respiratory tract and abscess formation in the lymph nodes of the head and neck. The name strangles comes from the fact that severely affected horses can develop such large abscesses in the throat area that they have difficulty breathing, appearing to be strangled.

The Bacterium and Its Behavior

Streptococcus equi subspecies equi is a gram-positive, beta-hemolytic bacterium. It produces several virulence factors that allow it to attach to the lining of the upper respiratory tract, evade the immune system, and cause tissue damage. The bacterium is highly contagious and spreads easily among horses that are housed together.

The organism is host-adapted to equids. While other Streptococcus equi subspecies can cause disease in other animals and occasionally in humans, the subspecies that causes strangles is essentially limited to horses, donkeys, and mules. This host specificity means that the disease does not pose a significant zoonotic risk to people, although basic hygiene measures are still recommended when handling infected horses.

How Strangles Spreads

Transmission occurs through direct contact with an infected horse or through indirect contact with contaminated objects. The bacteria are shed in nasal discharge and pus from ruptured lymph node abscesses. When an infected horse sneezes or coughs, droplets containing the bacteria can contaminate the immediate environment.

Indirect transmission is common. Shared water troughs, feed buckets, grooming equipment, halters, lead ropes, and human hands and clothing can all carry the bacteria from one horse to another. The bacteria can survive in the environment for several weeks, particularly in moist, dark conditions. This environmental persistence means that contaminated pastures, stalls, and equipment can serve as sources of infection for weeks after an infected horse has been removed.

The incubation period is typically 3 to 14 days after exposure. During this time, the horse shows no signs of illness but can already be shedding bacteria. This silent shedding period makes outbreak control particularly challenging because exposed horses may be infectious before they show any clinical signs.

The Carrier State

A critical feature of strangles is the ability of some horses to carry the bacteria without showing clinical signs. These carriers harbor the organism in their guttural pouches, which are large air-filled sacs connected to the Eustachian tubes in the horse's throat area. The guttural pouches provide a protected environment where the bacteria can persist for months or even years.

Carrier horses may shed bacteria intermittently, contaminating their environment and infecting other horses without appearing sick themselves. This carrier state is a major reason why strangles continues to cause outbreaks despite vaccination and biosecurity efforts. Eradication of the disease will not be possible until carriers are identified and treated or removed from the equine population.

Clinical Signs and Disease Progression

The clinical presentation of strangles varies depending on the age and immune status of the horse, the strain of bacteria involved, and the route and dose of exposure. Young horses typically develop more severe disease than older horses with some existing immunity.

Early Signs

The first sign of strangles is usually a sudden onset of fever, often reaching 103 to 106 degrees Fahrenheit. The fever typically appears 3 to 14 days after exposure. Affected horses become depressed, lose their appetite, and may show signs of upper respiratory discomfort.

A clear nasal discharge develops within a day or two of the fever and quickly becomes thick and purulent. The discharge is highly infectious and contaminates the environment as the horse sneezes and coughs. Some horses also develop conjunctivitis with discharge from the eyes.

Lymph Node Enlargement

The hallmark of strangles is enlargement of the lymph nodes of the head and neck. The submandibular lymph nodes, located under the jaw, and the retropharyngeal lymph nodes, located deeper in the throat area, are most commonly affected. These nodes become swollen, painful, and warm to the touch.

As the infection progresses, the lymph nodes enlarge and eventually form abscesses. These abscesses may rupture and drain thick, creamy pus through the skin. The pus is highly infectious and contaminates the environment. In some cases, the abscesses become so large that they interfere with breathing and swallowing, giving the disease its name.

Atypical and Severe Forms

Not all horses develop the classic signs of strangles. Some horses, particularly those with partial immunity, develop only a mild fever and slight nasal discharge without significant lymph node enlargement. These mild cases are easily missed, and the affected horses can spread the disease without being recognized as infected.

A severe form of the disease, sometimes called bastard strangles, occurs when the bacteria spread beyond the lymph nodes of the head and neck to other parts of the body. Abscesses can form in the lungs, liver, spleen, kidneys, and brain. This form of the disease is often fatal and is more common in young or immunocompromised horses.

Other complications include guttural pouch empyema, which is the accumulation of pus in the guttural pouches, and purpura hemorrhagica, an immune-mediated condition that causes severe swelling of the limbs, head, and body. Purpura hemorrhagica can occur weeks after the initial infection has resolved and is a medical emergency.

Disease Duration and Recovery

In uncomplicated cases, the clinical disease lasts approximately 2 to 3 weeks. The fever resolves as the abscesses mature and drain, and the horse gradually recovers. Most horses develop immunity after infection, but this immunity is not always complete or long-lasting. Horses can be reinfected, although subsequent infections are usually milder.

Some horses continue to shed bacteria for weeks or months after clinical recovery. These horses may be carriers and can infect other horses without showing signs themselves. Identifying and managing carriers is essential for preventing future outbreaks.

Diagnostic Testing

Accurate diagnosis of strangles is essential for implementing appropriate treatment and biosecurity measures. Diagnosis is based on clinical signs, laboratory testing, and sometimes postmortem examination. The choice of diagnostic test depends on the stage of the disease and the purpose of testing.

Clinical Diagnosis

In a horse with classic signs of strangles, including fever, nasal discharge, and enlarged lymph nodes of the head, a presumptive diagnosis can be made based on clinical examination alone. However, other diseases can cause similar signs, and laboratory confirmation is recommended whenever possible.

The differential diagnosis includes other respiratory infections such as equine influenza, equine herpesvirus, and other bacterial infections. Abscesses caused by other bacteria, such as Streptococcus zooepidemicus or Corynebacterium pseudotuberculosis, can also cause lymph node enlargement that resembles strangles.

Bacterial Culture

Bacterial culture has been the traditional method for diagnosing strangles. Samples are collected from nasal swabs, guttural pouch lavage, or pus from draining abscesses and submitted to a laboratory for culture. The bacteria are grown on selective media and identified based on their appearance and biochemical characteristics.

Culture is specific, meaning that a positive result confirms the diagnosis. However, culture is less sensitive than newer molecular methods, particularly in horses that are not actively shedding large numbers of bacteria. The sensitivity of culture depends on the quality of the sample, the stage of the disease, and the laboratory techniques used.

Polymerase Chain Reaction

Polymerase chain reaction testing has largely replaced culture as the gold standard for detecting Streptococcus equi subspecies equi. PCR detects the genetic material of the bacteria and is more sensitive than culture, meaning it can detect smaller numbers of bacteria in a sample.

PCR can be performed on the same types of samples used for culture, including nasal swabs, guttural pouch lavage, and pus. The test is rapid, with results often available within 24 to 48 hours. PCR is particularly useful for detecting carriers, which may shed very small numbers of bacteria that are difficult to grow in culture.

Point-of-care PCR assays are now available that can be performed in the field or in the clinic, providing results within hours. These tests allow rapid diagnosis and prompt implementation of biosecurity measures. However, point-of-care tests may be less sensitive than laboratory-based PCR, and negative results should be confirmed with laboratory testing in high-risk situations.

Serology

Serologic testing detects antibodies against Streptococcus equi subspecies equi in the blood. Serology is useful for identifying horses that have been exposed to the bacteria, even if they do not show clinical signs. It is particularly valuable for screening horses before they are moved to a new property or introduced to a group of horses.

The interpretation of serologic results requires careful consideration. A single positive result indicates exposure but does not distinguish between current infection, recent infection, carrier status, or vaccination. Paired samples taken 2 to 3 weeks apart can show rising antibody titers, which indicates recent infection.

Serology is less useful for diagnosing acute cases because antibodies take 1 to 2 weeks to develop after infection. A horse with clinical signs may have negative serology early in the disease course. Serology is also not useful for detecting carriers, as carrier horses may have low or undetectable antibody levels.

Diagnostic Sampling Guidelines

The choice of sample and timing of collection affect the accuracy of diagnostic testing. For horses with acute clinical signs, deep nasal swabs or guttural pouch lavage samples are recommended. For horses that have recovered from clinical disease, guttural pouch lavage is the preferred sample for detecting carriers.

Serial sampling is recommended for determining carrier status. A single negative sample does not rule out carriage, as carriers shed bacteria intermittently. Multiple samples taken over several weeks provide more reliable results. The 2018 consensus statement on strangles emphasizes the importance of serial sampling for detecting carriers and clearing horses from quarantine.

Treatment Approaches

Treatment of strangles is a subject of ongoing debate among veterinarians. The goals of treatment are to control transmission, eliminate infection, and provide future immunity. The approach depends on the stage of the disease and the individual horse's circumstances.

Supportive Care

For most horses with uncomplicated strangles, supportive care is the primary treatment. Affected horses should be rested and kept in a quiet, comfortable environment. Soft, palatable feed should be offered to encourage eating, as horses with throat abscesses may have difficulty swallowing.

Warm compresses applied to enlarged lymph nodes can help abscesses mature and rupture more quickly. Once an abscess has ruptured and is draining, the area should be kept clean to promote healing and prevent secondary infection. The pus from draining abscesses is highly infectious and must be handled with appropriate precautions.

Antibiotic Therapy

The use of antibiotics in horses with strangles is controversial. Antibiotics can reduce the severity and duration of clinical signs if given early in the disease course. However, antibiotic treatment during the abscess formation stage can interfere with the development of immunity and increase the risk of complications.

The 2018 consensus statement on strangles emphasizes the importance of judicious use of antibiotics in horses with strangles. Antibiotics are generally recommended for horses with severe disease, systemic signs, or complications such as bastard strangles. For horses with uncomplicated disease, antibiotics may be withheld to allow the immune system to respond and develop protective immunity.

The decision to use antibiotics should be made by a veterinarian based on the individual case. The choice of antibiotic, dose, and duration of treatment should be determined by the veterinarian and based on current evidence and local antimicrobial stewardship guidelines.

Management of Complications

Complications of strangles require specific treatment. Guttural pouch empyema may require flushing of the pouches through an endoscope to remove accumulated pus. This procedure is performed by a veterinarian and may need to be repeated several times.

Purpura hemorrhagica is a medical emergency that requires prompt veterinary attention. Treatment typically involves anti-inflammatory medications and supportive care. The prognosis for purpura hemorrhagica is guarded, and affected horses require intensive nursing care.

Treatment Outcomes

Most horses with uncomplicated strangles recover fully within 2 to 4 weeks. The prognosis is good for horses that receive appropriate supportive care and do not develop complications. The prognosis is more guarded for horses with bastard strangles, purpura hemorrhagica, or other severe complications.

Treatment outcomes depend on early recognition, prompt isolation, and appropriate veterinary care. Horses that recover from strangles develop immunity, but this immunity is not always complete or long-lasting. Reinfection is possible, although subsequent infections are usually milder.

Biosecurity Measures

Biosecurity is the most important aspect of strangles control. Effective biosecurity measures prevent the introduction of the disease to a property and limit its spread if an outbreak occurs. A comprehensive biosecurity plan should be in place before an outbreak happens.

Preventing Introduction

The most important biosecurity measure is quarantine of new and returning horses. All horses entering a property should be isolated for a minimum of 2 to 3 weeks before being introduced to the resident herd. During quarantine, horses should be monitored daily for fever and other signs of illness.

Quarantine is particularly important for horses returning from shows, sales, or other events where they may have been exposed to infected horses. The quarantine period should be extended if the horse has been exposed to a known case of strangles or if testing is being performed to rule out infection.

Daily Monitoring

Daily temperature checks are the key to controlling strangles outbreaks. Horses should have their temperature taken at the same time each day, and any horse with a fever should be immediately isolated and examined by a veterinarian. Early detection of fever allows prompt isolation before the horse becomes contagious.

Temperature monitoring should be performed for all horses on a property during an outbreak, including horses that appear healthy. The 2023 review of Streptococcus equi subspecies equi emphasizes that daily temperature checking and isolation of febrile horses is the key to controlling outbreaks.

Isolation and Cohorting

When strangles is suspected or confirmed, affected horses should be isolated immediately. Isolation facilities should be separate from the main barn and should have dedicated equipment, including feed buckets, water buckets, grooming tools, and cleaning supplies. The isolation area should be clearly marked, and access should be restricted to essential personnel.

The traffic light system is a useful framework for managing horses during an outbreak. Red group horses are those with clinical signs or positive test results. Yellow group horses are those that have been exposed to infected horses but do not show signs. Green group horses are those with no known exposure. Each group should be housed separately, and personnel should work with the green group first and the red group last.

Hygiene and Disinfection

Hand hygiene is critical for preventing the spread of strangles. Personnel should wash their hands thoroughly with soap and water or use an alcohol-based hand sanitizer after handling each horse. Disposable gloves should be worn when handling infected horses or contaminated equipment.

Protective clothing, including coveralls and boots, should be worn when working with infected horses. Clothing and boots should be changed or disinfected before moving to other horses. Footbaths containing disinfectant can help prevent the spread of bacteria on boots.

The environment should be cleaned and disinfected regularly. Stalls, water troughs, feed buckets, and grooming equipment should be cleaned with soap and water to remove organic material, then disinfected with an appropriate disinfectant. The bacteria are susceptible to most common disinfectants, including bleach, chlorhexidine, and accelerated hydrogen peroxide.

Waste Management

Pus and nasal discharge from infected horses are highly infectious and must be handled carefully. Disposable materials such as bandages, gauze, and gloves should be placed in sealed bags and disposed of properly. Bedding from infected stalls should be composted or disposed of in a way that prevents contamination of other areas.

Manure from infected horses should be handled with care. The bacteria can survive in manure for several weeks, and contaminated manure can spread the disease if it is spread on pastures where other horses graze. Manure from infected horses should be composted or disposed of separately from manure from healthy horses.

Biosecurity Checklist for Barns

A written biosecurity checklist helps ensure that all necessary measures are implemented consistently. The following checklist can be adapted to individual properties and situations.

Before an Outbreak

• Maintain a written biosecurity plan that is reviewed and updated regularly
• Designate a quarantine area that is separate from the main barn
• Stock appropriate disinfectants, protective clothing, and disposable supplies
• Train all personnel on biosecurity protocols and hand hygiene
• Establish a relationship with a veterinarian who can provide guidance during an outbreak
• Keep records of all horses on the property, including identification, vaccination status, and movement history

During an Outbreak

• Isolate all horses with fever or clinical signs immediately
• Take temperatures of all horses daily and record the results
• Implement the traffic light system to group horses by exposure status
• Restrict movement of horses on and off the property
• Use dedicated equipment for each group of horses
• Clean and disinfect stalls, equipment, and common areas regularly
• Wear protective clothing and practice strict hand hygiene
• Dispose of infectious waste properly
• Communicate with all stakeholders, including owners, staff, and veterinarians

After an Outbreak

• Continue monitoring all horses for fever and clinical signs for at least 4 weeks after the last case
• Test recovered horses to identify carriers before releasing them from quarantine
• Clean and disinfect all facilities and equipment thoroughly
• Review the biosecurity plan and identify areas for improvement
• Consider vaccination for horses at high risk of exposure

Records and Measurements

Accurate record keeping is essential for managing strangles outbreaks and preventing future cases. Records should document clinical signs, test results, treatments, and biosecurity measures.

Temperature Records

Daily temperature records are the most important monitoring tool during an outbreak. Each horse's temperature should be recorded at the same time each day, and any elevation above normal should be noted. Normal equine temperature ranges from 99 to 101 degrees Fahrenheit, but individual horses may vary.

Temperature records should include the horse's identification, the date and time of measurement, the temperature reading, and any other clinical signs observed. These records help identify febrile horses early and track the progression of the outbreak.

Testing Records

Records of diagnostic testing should include the type of test performed, the date of collection, the sample type, the laboratory that performed the test, and the results. These records are essential for determining when horses can be released from quarantine and for identifying carriers.

Serial testing records are particularly important for clearing horses from quarantine. The results of multiple tests over time provide more reliable information than a single test result.

Treatment Records

Treatment records should document all medications administered, including the drug, dose, route, and duration of treatment. These records are important for monitoring the response to treatment and for ensuring that withdrawal periods are observed if applicable.

Treatment records should also document supportive care measures, such as warm compresses, wound care, and nutritional support. These records help ensure that all aspects of the horse's care are addressed.

Movement Records

Records of horse movements on and off the property are essential for tracing the source of an outbreak and identifying horses that may have been exposed. Movement records should include the horse's identification, the date of movement, the destination or origin, and the reason for movement.

During an outbreak, movement records help identify horses that need to be quarantined or tested. They also help authorities trace the spread of the disease if multiple properties are affected.

Common Failure Patterns

Despite the availability of effective biosecurity measures, strangles outbreaks continue to occur. Understanding common failure patterns can help horse owners and veterinarians avoid mistakes that allow the disease to spread.

Delayed Recognition

One of the most common failures is delayed recognition of the disease. Early signs of strangles, including fever and mild nasal discharge, can be mistaken for other respiratory infections. By the time the characteristic lymph node enlargement develops, the disease has already spread to other horses.

Daily temperature monitoring is the most effective way to detect strangles early. Horses with fever should be isolated immediately, even before a diagnosis is confirmed. Waiting for laboratory confirmation before isolating a febrile horse allows the disease to spread.

Incomplete Quarantine

Quarantine is only effective if it is implemented correctly. Common mistakes include placing quarantined horses in facilities that are too close to the main barn, allowing shared airspace or equipment, and failing to enforce quarantine protocols.

Quarantine should be truly separate from the main barn. Personnel should work with quarantined horses last, and dedicated equipment should be used for quarantined horses. Visitors should not have access to quarantined horses, and horses should not be moved in or out of quarantine without veterinary approval.

Inadequate Disinfection

The bacteria that cause strangles can survive in the environment for weeks. Inadequate cleaning and disinfection allows the bacteria to persist and infect new horses. Common mistakes include failing to remove organic material before disinfecting, using disinfectants at incorrect concentrations, and neglecting to disinfect all surfaces and equipment.

Disinfectants are inactivated by organic material, so surfaces must be cleaned thoroughly before disinfection. Disinfectants should be used at the concentration and contact time recommended by the manufacturer. All surfaces that may have been contaminated, including walls, floors, feed buckets, and water troughs, should be disinfected.

Failure to Identify Carriers

Carrier horses are a major source of new outbreaks. Horses that have recovered from strangles may continue to shed bacteria for months, and some carriers show no signs of illness. Failure to test recovered horses for carrier status allows the disease to persist on the property.

Testing recovered horses for carrier status is essential for preventing future outbreaks. Guttural pouch lavage and PCR testing are the most reliable methods for detecting carriers. Serial testing over several weeks provides the most accurate results.

Poor Communication

Effective communication is essential during an outbreak. Failure to communicate with all stakeholders, including owners, staff, veterinarians, and neighboring properties, can lead to confusion and inconsistent implementation of biosecurity measures.

A designated person should be responsible for coordinating the outbreak response and communicating with all parties. Regular updates should be provided as the situation evolves. Neighboring properties should be notified if there is a risk of disease spread.

Welfare and Safety Considerations

Strangles causes significant welfare concerns for affected horses. The disease is painful, and affected horses may have difficulty eating, drinking, and breathing. Prompt recognition and treatment reduce suffering and improve outcomes.

Pain Management

Horses with strangles experience pain from lymph node enlargement and abscess formation. Pain management is an important aspect of supportive care. Anti-inflammatory medications may be recommended by a veterinarian to reduce pain and fever.

Warm compresses applied to enlarged lymph nodes can provide comfort and help abscesses mature. Once an abscess has ruptured, keeping the area clean and protected promotes healing and reduces discomfort.

Nutritional Support

Horses with throat abscesses may have difficulty eating and drinking. Soft, palatable feed should be offered to encourage eating. Hay can be soaked to make it easier to chew and swallow. Fresh water should be available at all times, and some horses may prefer warm water during cold weather.

Horses that are unable to eat or drink adequately may require nutritional support. A veterinarian can recommend appropriate feeding strategies, including the use of complete feeds or supplements.

Human Safety

Strangles is not considered a significant zoonotic disease, but basic hygiene measures are recommended when handling infected horses. The bacteria can cause infection in people with open wounds or compromised immune systems, although this is rare.

Personnel should wear gloves when handling infected horses or contaminated equipment. Hands should be washed thoroughly after handling horses. People with open wounds or immune suppression should avoid contact with infected horses.

Emotional Impact on Owners

Strangles outbreaks are stressful for horse owners. The disease can cause significant financial costs, movement restrictions, and emotional distress. Owners may feel frustrated by the limitations imposed by quarantine and concerned about the health of their horses.

Veterinarians should provide clear, accurate information and support to owners during an outbreak. Regular communication and realistic expectations help owners cope with the challenges of managing the disease.

Limitations and Uncertainties

Despite advances in diagnosis and treatment, several limitations and uncertainties remain in the management of strangles.

Diagnostic Limitations

No diagnostic test is perfect. Culture is specific but less sensitive than PCR. PCR is sensitive but can detect non-viable bacteria, leading to false-positive results in horses that have cleared the infection. Serology cannot distinguish between infection and vaccination, and results must be interpreted carefully.

The sensitivity of diagnostic testing depends on the quality of the sample and the timing of collection. A single negative test does not rule out infection, particularly in carriers that shed bacteria intermittently. Serial testing over several weeks provides the most reliable results.

Treatment Uncertainties

The optimal approach to antibiotic therapy for strangles remains uncertain. The 2018 consensus statement emphasizes judicious use of antibiotics, but there is no universally accepted protocol. The decision to use antibiotics should be made on a case-by-case basis by a veterinarian.

The role of vaccination in strangles control is also uncertain. Vaccines are available, but they do not provide complete protection, and their use is controversial in some situations. The 2018 consensus statement reviews current vaccine technology and emphasizes the importance of linking vaccination with disease control and prevention programs.

Carrier Detection Challenges

Identifying carriers is essential for preventing future outbreaks, but carrier detection is challenging. Carriers shed bacteria intermittently, and a single negative test does not rule out carriage. Serial testing over several weeks is recommended, but this is time-consuming and expensive.

The guttural pouches are the primary site of persistent infection, but the bacteria can also persist in other locations. The optimal sampling protocol for carrier detection is still being refined, and new evidence is strengthening guidelines for serial sampling and disinfection protocols.

Emerging Strains

The global population of Streptococcus equi subspecies equi is dynamic, and new strains are constantly emerging. Studies have identified novel strains with variations in virulence factors and antigenic properties. These emerging strains may affect the effectiveness of vaccines and diagnostic tests.

The 2013 review of strangles eradication notes that emerging data illustrates the dynamism of the global S. equi population and potential consequences for the effectiveness of currently available vaccines. Ongoing surveillance is needed to monitor the emergence of new strains and adapt control strategies accordingly.

Professional Escalation Criteria

Knowing when to seek veterinary assistance is essential for managing strangles effectively. The following situations warrant immediate veterinary attention.

Urgent Veterinary Care

• Any horse with a fever of 103 degrees Fahrenheit or higher, particularly if other horses on the property are also febrile
• Any horse with difficulty breathing, which may indicate severe lymph node enlargement or bastard strangles
• Any horse with swelling of the limbs, head, or body, which may indicate purpura hemorrhagica
• Any horse that is unable to eat or drink for more than 24 hours
• Any horse with signs of colic or other systemic illness

Veterinary Consultation

• Any horse with nasal discharge or lymph node enlargement that persists for more than 48 hours
• Any horse that has been exposed to a confirmed case of strangles
• Any horse that is being considered for movement to a new property
• Any horse that has recovered from strangles and is being considered for release from quarantine

Laboratory Testing

• Confirmation of diagnosis in horses with clinical signs consistent with strangles
• Screening of horses before movement to a new property
• Testing of recovered horses to identify carriers
• Investigation of outbreaks to determine the source of infection

Frequently Asked Questions

What is the difference between strangles and other respiratory infections in horses?

Strangles is caused by the bacterium Streptococcus equi subspecies equi and is characterized by fever, nasal discharge, and abscess formation in the lymph nodes of the head and neck. Other respiratory infections, such as equine influenza and equine herpesvirus, are caused by viruses and typically do not cause lymph node abscesses. The diagnosis is confirmed by laboratory testing, including PCR and culture.

How long does a horse with strangles remain contagious?

A horse with strangles can shed bacteria from the onset of fever until several weeks after clinical recovery. Some horses become carriers and shed bacteria intermittently for months or even years. The contagious period varies between horses, and testing is required to determine when a horse is no longer shedding bacteria.

Can a horse get strangles more than once?

Yes, horses can be reinfected with strangles. Infection stimulates an immune response, but this immunity is not always complete or long-lasting. Subsequent infections are usually milder than the first infection. Vaccination can provide some protection but does not prevent all cases of the disease.

Is strangles contagious to humans?

Strangles is not considered a significant zoonotic disease. The bacterium is host-adapted to equids and rarely causes disease in humans. However, basic hygiene measures, including hand washing and wearing gloves, are recommended when handling infected horses. People with open wounds or compromised immune systems should avoid contact with infected horses.

How is strangles diagnosed?

Strangles is diagnosed based on clinical signs and laboratory testing. PCR testing of nasal swabs or guttural pouch lavage samples is

Related Veterinary Guides

• Recognizing Normal Vital Signs in Horses
• Leptospirosis in Dogs: Clinical Signs, Diagnosis, and Updated Vaccination Protocols
• Leptospirosis in Dogs: Clinical Signs, Diagnosis, and Zoonotic Risk Management
• Johne's Disease in Sheep: Clinical Signs, Diagnosis, and Control
• Broiler Avian Influenza: Diagnosis and Biosecurity

References and Further Reading

• Merck Veterinary Manual. Merck Veterinary Manual.
• Animal Health and Welfare. World Organisation for Animal Health.
• Streptococcus equi Infections in Horses: Guidelines for Treatment, Control, and Prevention of Strangles-Revised Consensus Statement.. Journal of veterinary internal medicine, 2018.
• Equine respiratory pharmacology.. The Veterinary clinics of North America. Equine practice, 1999.
• Streptococcus equi Subspecies equi.. The Veterinary clinics of North America. Equine practice, 2023.
• Strangles: taking steps towards eradication.. Veterinary microbiology, 2013.
• Decreased Clinical Severity of Strangles in Weanlings Associated with Restricted Seroconversion to Optimized Streptococcus equi ssp equi Assays.. Journal of veterinary internal medicine, 2018.
• Update on Streptococcus equi subsp equi infections.. The Veterinary clinics of North America. Equine practice, 2015.
• An outbreak of strangles in young ponies.. The Veterinary record, 1993.
• Novel Streptococcus equi strains causing strangles outbreaks in Arabian horses in Egypt.. Transboundary and emerging diseases, 2020.
• Streptococcus Equi: A rare cause of cellulitis and bacteremia in human.. 2026.
• Updates on Diagnosis and Treatment of Guttural Pouch Conditions.. 2026.
• Gut virome derived bacteriophage endolysin Lys572 can effectively control Streptococcus suis in refrigerated and thawed pork.. 2026.
• Fatal Septic Shock Caused by Enterotoxigenic &lt,i&gt,Escherichia coli&lt,/i&gt, O128 and Rare Polymicrobial Co-Infection with &lt,i&gt,Streptococcus equi&lt,/i&gt, Subsp. &lt,i&gt,zooepidemicus&lt,/i&gt,, &lt,i&gt,Klebsiella oxytoca&lt,/i&gt, and &lt,i&gt,Enterococcus durans&lt,/i&gt, in a Patient with Liver Cirrhosis: A Case Report.. 2026.
• Two cases of Streptococcus equi subspecies zooepidemicus bacteremia diagnosed in a French hospital within a short space of time.. 2026.
• [Management and hygiene measures during an outbreak of herpes, influenza, strangles or infections with multidrug resistant bacteria].. Tierarztliche Praxis. Ausgabe G, Grosstiere/Nutztiere, 2022.
• Validation of a point-of-care polymerase chain reaction assay for detection of Streptococcus equi subspecies equi in rostral nasal swabs from horses with suspected strangles.. The Canadian veterinary journal = La revue veterinaire canadienne, 2021.
• An outbreak of strangles in arabian horses in saudi arabia: Epidemiology, clinical signs and treatment outcomes. International Journal of Veterinary Science, 2021.
• Vaccination of horses against strangles using recombinant antigens from Streptococcus equi. Vaccine, 2007.

This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.