Glanders is one of the oldest diseases known to affect equines. It is a highly contagious and fatal disease that affects horses, donkeys, and mules, caused by infection with Burkholderia mallei bacteria. Glanders poses a significant zoonotic threat, as it can also infect humans and other animals. [1][2]

Affected horses typically develop symptoms including high fever, thick nasal discharge, skin lesions, and respiratory distress. Signs vary depending on the type of infection and its severity, but collectively indicate a serious and potentially fatal condition. [3]

There are limited treatment options for infected horses. Most horses are humanely euthanized to prevent the spread of the disease to other horses or humans.

Strict regulations have led to the elimination of glanders in several regions, such as North America. However, global travel and importation of horses pose an ongoing risk of reintroducing the disease into areas where it has been otherwise eradicated. [4]

Glanders Transmission in Horses

Burkholderia mallei is a rod-shaped bacterium that primarily spreads through direct transmission. It thrives in moist environments, but is susceptible to heat and disinfectants, which limits its survival outside the host. [2][5][6]

Horses can contract glanders through direct contact with infected animals, including exposure to nasal discharge, saliva, and other bodily fluids. The bacteria can infect horses through mucous membranes, inhalation or skin abrasions. [7]

Indirect transmission occurs when horses come into contact with contaminated objects (fomites) that carry secretions from infected horses. Examples of objects include grooming equipment, feed and water containers, stables, and human hands that have handled infected animals, materials, or feet that have walked through a contaminated area.

The incubation period, or the time between exposure to the bacterium and the onset of signs, can vary significantly. Glanders symptoms in horses typically develop within a couple of weeks to several months after exposure. [3][7]

Due to its severe impact and the lack of effective treatment, glanders is a notifiable disease in many countries, requiring immediate reporting to animal health authorities. In areas where it is found, stringent measures, including quarantine and euthanasia of affected animals, are usually enforced to prevent its spread.

Types of Glanders

Glanders presents in three forms, classified based on the location of the initial infection: nasal, pulmonary, and skin (“farcy”).

Each form exhibits distinct clinical signs that range in severity. It’s important to note that horses can develop multiple forms of glanders simultaneously. [7][8]

All infected horses typically exhibit signs such as: [2][3]

  • Fever (up to 106°F or 41°C)
  • Lethargy
  • Severe weight loss

Nasal Form

This acute form of glanders affects the lining of the nose. Nodules develop in the nasal septum and nostrils, spreading into the upper respiratory tract and creating deep ulcers.

As a result, affected horses may exhibit symptoms including: [3]

Pulmonary Form

Pulmonary glanders is another acute form of the disease. In this form of the disease, small nodules develop in the lung tissue and cause inflammation.

In severe cases, this can lead to pneumonia or lung tissue consolidation, where air-filled spaces fill with fluid, blood, or inflammatory cells, making the lung tissue denser.

This impairs lung function, affecting the horse’s breathing. [3]

Cutaneous Form (Farcy)

Cutaneous glanders (also known as farcy) affects the horse’s skin and is the only chronic form of the infection. Signs of farcy tend to appear on skin of the limbs, inner thighs and belly.

Nodules develop on the lymphatic vessels under the skin and break down into ulcers that excrete thick yellow pus. These ulcers heal very slowly and continuously excrete highly contagious discharge. [2][3]

Chronic vs. Acute Glanders

Acute glanders, commonly observed in donkeys, is characterized by a rapid onset of symptoms and severe progression, often resulting in fatality within days to weeks. Affected animals exhibit high fevers, weight loss, large volumes of thick, yellow nasal discharge, and respiratory distress. [2]

In contrast, chronic glanders is more prevalent in horses and presents with a slower onset, with intermittent symptoms appearing over an extended period. Affected horses develop nodules and ulcers on the skin and can live for years while continuously spreading the bacteria. [2] While affected horses may live with the infection for a long time, glanders is eventually fatal in all cases.

It’s important to note that mules are susceptible to both acute and chronic forms of glanders.

Risk Factors

Understanding the risk factors associated with glanders in horses is helpful for effective disease management and prevention. The following factors may increase the likelihood of horses developing glanders: [8]

  • Overcrowding: horses kept in close quarters, such as in stables, breeding farms, and racing facilities, are at higher risk due to increased exposure to the bacteria from infected animals
  • Endemic disease: horses in regions where glanders is endemic, such as parts of Asia and the Middle East are at higher risk. In these areas, the disease is more prevalent, increasing the likelihood of exposure
  • Poor biosecurity: inadequate quarantine procedures for new or returning horses, insufficient disinfection of equipment, and lack of proper isolation of sick animals can facilitate the spread of glanders
  • Contaminated water and feed: sharing water and feed sources that have been contaminated by infected horses significantly increases the risk of transmission
  • Travel: international movement of horses for trade, competition, or breeding without thorough health checks can introduce glanders to new areas; horses transported from or through regions with endemic glanders are particularly at risk
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Glanders in Other Species

While glanders primarily affects horses and donkeys, it can also infect a variety of other species. It is worth noting that cattle and pigs are not susceptible to glanders. Animals that can develop symptomatic illness include: [2][7][9][10]{ref n=”11″]

  • Humans: while less common, humans can contract glanders through direct contact with infected animals or contaminated materials; the disease can be severe and potentially fatal in humans if not treated promptly because glanders can develop multiple paths of antibiotic resistance
  • Carnivores: wild and domestic carnivores, such as lions, tigers, and domestic cats, can contract glanders, typically through ingestion of infected meat
  • Rodents: some rodent species are susceptible to glanders and can serve as reservoirs for the disease, contributing to its spread
  • Camels: dromedaries can also be affected by glanders, showing symptoms similar to those seen in equines, such as nasal discharge and skin lesions

In rare cases, goats, dogs, and rabbits can also be affected by glanders. [12]

Geographic Distribution of Glanders

To prevent the introduction and spread of glanders, many regions have implemented strict import regulations and surveillance programs for horses transported across borders.

These measures include mandatory testing and quarantine periods for horses imported from regions where glanders is known to occur. [2][13]

As a result, glanders infection has been successfully eliminated from several countries and regions, such as North America, Australia, Japan, and Western Europe. [4][14]

Glanders is still present in the following countries: [3][15]

  • Iraq
  • Nepal
  • Pakistan
  • China
  • India
  • Mongolia
  • Brazil
  • United Arab Emirates
  • Turkey

Globalization and increased international horse travel heightens the risk of spreading glanders to new regions. The large-scale transport of horses and materials, even with stringent regulations, poses a substantial risk of introducing this infectious disease to areas previously unaffected. [4]

If a horse is suspected of having glanders, government animal health officials must be notified immediately. Early detection and containment efforts are essential to mitigate the impact on equine and human health, as well as the economy and international trade.

The above description of global glanders distribution is accurate at the time of publication but may not be complete. Always review local guidelines and regulations before arranging transportation for your horse.

Diagnosis

Diagnosing glanders in horses and donkeys involves a comprehensive approach, including physical examination, laboratory tests, and specific procedures to confirm the presence of Burkholderia mallei.

Prior to laboratory testing, veterinarians typically assess the horse for common signs of glanders, such as fever, nasal discharge, skin lesions, and respiratory distress.

Diagnostic Tests

Various laboratory tests can confirm glanders in horses, including the complement fixation test (CFT), polymerase chain reaction (PCR) tests, and bacterial cultures. [1][3]

Complement Fixation Test (CFT)

The Complement Fixation Test is highly accurate and often used to confirm glanders infection in horses. [1][7][16]

This serum test identifies antibodies to Burkholderia mallei in horse blood, demonstrating 90-95% sensitivity in symptomatic horses. A positive result from this test indicates that the horse has been exposed to the bacteria. [1][7][16]

However, the CFT can yield false-negative results in certain cases, including in young horses and pregnant mares. A false negative means the test returns a negative result even though the horse is actually infected with glanders.

False-positive results also occur in about 1% of cases due to cross-reactions with other antibodies. In such cases, the test returns a positive result even though the horse does not have a glanders infection.

False positives can lead to financial losses, as infected horses need to be euthanized. Conversely, false negatives might introduce glanders into healthy horse populations.

Polymerase Chain Reaction (PCR)

PCR testing is a highly sensitive and specific molecular technique that detects the genetic material of B. mallei in clinical samples.

This test can identify the presence of the bacterium even in the early stages of infection and is useful for confirming the disease when other tests are inconclusive. [1][7]

Bacterial Cultures

Culturing involves growing B. mallei from samples such as nasal discharge, skin ulcers, or abscesses in a laboratory. This method provides definitive evidence of infection by isolating and identifying the bacterium. [1]

This method requires specialized laboratory facilities and can take several days to yield results. Cultures may not be possible if samples are taken from horses that are early in infection, complicating the diagnostic process.

Therefore, relying solely on culture-based methods for early diagnosis may not always be feasible or effective. [4]

Treatment and Prognosis

Currently, effective treatment options for horses with glanders are lacking. Further, treating the disease is not recommended and often forbidden by local regulations.

This is due to the risk of horses becoming carriers, potentially spreading the disease to others, even if they show improvement. [7]

Euthanasia is often the only course of action to prevent the spread of glanders and protect the health of both animals and humans. [1][3][8]

The prognosis for glanders is grave, especially in acute cases, with the disease progressing rapidly and often leading to fatality within days to weeks.

Prevention and Control

Preventing the spread of glanders in horses involves stringent measures to reduce transmission and quickly detect and manage cases. Key strategies for prevention and control include: [2][7][8]

  • Quarantine and Surveillance: strict quarantine protocols for suspected cases or horses returning from endemic areas help control the spread of infection. Regular surveillance programs monitor equine populations and prompt appropriate action if infection is suspected.
  • Biosecurity: implementing robust biosecurity measures in equine facilities, including proper disinfection of equipment, isolation of sick animals, and access restriction.
  • Hygiene: when horses are diagnosed with glanders, euthanasia is necessary to prevent further spread. Ensuring proper disposal of bodies and any contaminated materials minimizes environmental contamination.
  • Public Education: experts including veterinarians and public health officials work together to raise public awareness and educate stakeholders, including horse owners, about glanders.
  • Compliance: adherence to international regulations regarding international transport is fundamental to stopping the spread of glanders. Notify officials of potential cases to further aid prevention efforts.

Even with strict precautions and regulations in place, there is still a risk of glanders spreading to new areas. In places where glanders is endemic, horses are tested, and any positive cases result in euthanasia. These steps are crucial to prevent the disease from spreading within the population. [2]

Zoonotic Risk of Glanders

Glanders is much less common in humans than horses, but poses a significant health risk when contracted. Humans can become infected through direct contact with infected animals or contaminated materials.

Typically, glanders is transmitted to humans through skin abrasions or inhalation of bacteria. Ingestion of contaminated food and water, as well as human-to-human transmission, are uncommon routes of transmission. [5]

In humans, the disease often begins with fever as the initial symptom, followed by the development of pneumonia, and nodules and abscesses on the skin. The acute form progresses rapidly and can be fatal within 7 to 10 days without intervention. Humans can also develop chronic glanders with intermittent symptoms over an extended period. [17]

Treatment is often delayed due to the rarity of human cases, but antibiotic therapy has shown effectiveness. Recovery times are characteristically slow, especially in cases of delayed diagnosis and systemic infection. [17]

Summary

Glanders is a highly contagious and fatal disease affecting horses, donkeys, and mules, caused by the bacterium Burkholderia mallei.

  • The disease can also infect humans and poses a significant zoonotic threat.
  • Clinical signs of glanders typically include fever, respiratory distress, ulcers on the skin, weight loss, and purulent nasal discharge.
  • Horses with glanders should not be treated, and euthanasia should be conducted to prevent the spread of disease.
  • Prevention measures include strict quarantine and biosecurity protocols in equine facilities.

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References

  1. Abreu, D. C. et al., Systematic Monitoring of Glanders-Infected Horses by Complement Fixation Test, Bacterial Isolation, and PCR. Vet Anim Sci. 2020.
  2. Khan, I. et al., Glanders in Animals: A Review on Epidemiology, Clinical Presentation, Diagnosis and Countermeasures: Glanders in Solipeds. Transboundary and Emerging Diseases. 2013.
  3. Timoney, J. F., Glanders in Horses and Other Animals. MDS Veterinary Manual. 2020.
  4. Young, A., Glanders. UC Davis School of Veterinary Medicine. 2020.
  5. Van Zandt, K. E. et al., Glanders: An Overview of Infection in Humans. Orphanet J Rare Dis. 2013.
  6. Lopez, J. et al., Characterization of Experimental Equine Glanders. Microbes and Infection. 2003. View Summary
  7. Kennedy, M. and Munroe, G., Glanders in Horses (Equis). Vet Lexicon.
  8. Glanders. World Organisation for Animal Health.
  9. Khaki, P. et al., Glanders Outbreak at Tehran Zoo, Iran. Iran J Microbiol. 2012.
  10. Wernery, U. et al., Natural Burkholderia Mallei Infection in Dromedary, Bahrain. Emerg Infect Dis. 2011.
  11. Rhodes, K. A. and Schweizer, H.P., Antibiotic resistance in Burkholderia species. Drug Resist Updat. 2016.
  12. Timoney, J. F., Glanders (Farcy) in Dogs. MDS Veterinary Manual. 2018.
  13. Derbyshire, B., The Eradication of Glanders in Canada. Can Vet J. 2002. View Summary
  14. Agency, C. F. I., Equine Glanders Fact Sheet. 2018.
  15. Mota, R. A. and Junior, J. W. P., Current Status of Glanders in Brazil: Recent Advances and Challenges. Braz J Microbiol. 2022. View Summary
  16. Dehghan Rahimabadi, P. et al., Serological and Bacteriological Surveillance of Glanders Among Horses in Central Region of Iran. J Equine Vet Sci. 2023. View Summary
  17. Nguyen, H. N. et al., Glanders and Melioidosis. In: StatPearls. StatPearls Publishing. 2024. View Summary