Glanders is a contagious, often fatal, zoonotic disease that primarily affects horses and other equids. It is caused by the bacterium Burkholderia mallei. Although previously eradicated or effectively controlled in many parts of the world, glanders is reemerging in some areas. Clinical signs include purulent nasal discharge, nasal mucosal ulceration, lung lesions, and ulcerating nodules along subcutaneous lymphatics; however, animals with atypical signs and carrier animals might not be recognized. Diagnosis is based on clinical evaluation, complement fixation test reaction, culture results, and PCR assay results. Control consists of isolating and culling affected animals.
Glanders is a contagious, usually fatal disease of Equidae caused by the bacterium Burkholderia mallei, a pathoadaptive clone derived from Burkholderia pseudomallei. Glanders can be either acute or chronic and is characterized by serial development of nodules in the upper respiratory tract, lungs, and skin. The cutaneous form of the disease is known as farcy. Infection of other species, such as camels, tigers, and lions, is uncommon but usually fatal. The organism can infect humans, and because the fatality rate for untreated septicemia cases in humans is 40−95%, B mallei is considered a potential bioterrorism agent.
Glanders is one of the oldest diseases on record and was once prevalent worldwide. It is now eradicated or effectively controlled in many countries, including the US. Starting in 2004, however, glanders began reemerging, first in the Middle East, then in India, followed by a reported case in Europe in 2006. Its reemergence is largely due to the (illegal) transport of horses globally for trade and international competitions, which increases the risk of disease transmission. Glanders is one of the 4 diseases the World Organisation for Animal Health (WOAH) recommends testing for before international movement of horses. In addition, importing equids (temporarily or permanently) into glanders-free countries requires at least a veterinary health certificate and a valid legal passport.
Countries and regions where the disease has been reemerging include the Middle East (Kuwait, Lebanon, Iran, Iraq, United Arab Emirates, Bahrain), Afghanistan, Pakistan, India, Mongolia, Nepal, the Philippines, China, South America (Bolivia, Brazil), Africa (Eritrea, Ethiopia), Turkey, and Russia. Several animals have tested positive for glanders upon importation into Germany and the US.
Etiology of Glanders in Horses and Other Equids
Burkholderia mallei is a clonal, gram-negative, facultative, intracellular, obligate bacterium that is present in nasal exudate and discharge from ulcerated skin. Glanders is commonly contracted via the following routes:
ingestion of food or water contaminated with nasal discharge from infected (carrier) animals
contact with contaminated harness components
ingestion of infected horse meat
The organism is susceptible to heat, light, and disinfectants; survival in a contaminated area is limited to 1–2 months. Humid, wet conditions favor survival. A polysaccharide capsule, important in virulence, enhances environmental survival.
Clinical Findings of Glanders in Horses and Other Equids
Equine glanders can present in different stages and forms. Donkeys and mules tend to be affected acutely and more severely than horses. After an incubation period of 3 days to 2 weeks, acutely affected patients usually show the following clinical signs:
septicemia
high fever (as high as 41°C [106°F])
weight loss
thick, mucopurulent, yellowish nasal discharge
respiratory signs
Death occurs within a few days.
Chronic glanders is a common, debilitating condition in horses that is characterized by nodular or ulcerative lesions that gradually progress over time. Latent infected carriers, living for years without clinical signs or with low-grade fever, continue to disseminate the organism.
Chronic glanders can occur in nasal, pulmonary, and cutaneous forms, and a patient can be affected by more than one form at a time. In the nasal form, nodules develop in the nasal septal mucosa and lower parts of the turbinates. Nodules degenerate into deep ulcers with raised irregular borders. Characteristic star-shaped cicatrices remain after ulcers heal. In the early stage, submaxillary lymph nodes are enlarged and edematous; later, they adhere to skin or deeper tissues.
In the pulmonary form, small, tubercle-like nodules with caseous or calcified centers surrounded by inflammatory zones form in the lungs. With extensive disease, pulmonary consolidation and pneumonia can occur. Nodules may break down and discharge their contents into bronchioles, extending infection to the upper respiratory tract.
In the cutaneous form (called farcy), nodules appear along lymph vessels (see abdomen image), particularly those of the extremities (see axilla and forelegs image). Nodules degenerate and form ulcers that discharge highly infectious, sticky pus (see ulcers with discharge image). The liver and spleen may also develop typical nodular lesions. Histological analysis may show vasculitis, thrombosis, and infiltration of degenerating inflammatory cells.
Typical signs of cutaneous glanders (farcy) in a horse. Note the nodules and swollen cutaneous lymph vessels along the abdominal wall. Note also the swollen scrotum between the hindlegs.
Courtesy of Dr. Elisabeth-Lidwien Verdegaal, University of Adelaide.
Cutaneous glanders (farcy) in a horse. Note the nodules and draining tracts along lymph vessels of the axilla and forelegs.
Courtesy of Dr. Elisabeth-Lidwien Verdegaal, University of Adelaide.
Cutaneous glanders (farcy) in a horse. Note the ulceration and highly infectious, sticky, purulent discharge.
Courtesy of Dr. Elisabeth-Lidwien Verdegaal, University of Adelaide.
Typical signs of cutaneous glanders (farcy) in a horse. Note the nodules and swollen cutaneous lymph vessels along the abdominal wall. Note also the swollen scrotum between the hindlegs.
Courtesy of Dr. Elisabeth-Lidwien Verdegaal, University of Adelaide.
Cutaneous glanders (farcy) in a horse. Note the nodules and draining tracts along lymph vessels of the axilla and forelegs.
Courtesy of Dr. Elisabeth-Lidwien Verdegaal, University of Adelaide.
Cutaneous glanders (farcy) in a horse. Note the ulceration and highly infectious, sticky, purulent discharge.
Courtesy of Dr. Elisabeth-Lidwien Verdegaal, University of Adelaide.
Diagnosis of Glanders in Horses and Other Equids
Presumptive: clinical evaluation
Definitive: complement fixation test, competitive ELISA, culture, and PCR assay
Presumptive diagnosis of glanders is based on clinical observation of cutaneous nodules exuding honeylike discharge or of nasal discharge with nasal mucosal ulceration. The typical nodules, ulcers, scar formation, and patient's debilitated condition may be sufficient for clinical diagnosis.
Because clinical signs usually do not develop until the disease is well advanced, specific diagnostic tests should be performed as soon as glanders is suspected. Culture of B mallei from lesions can confirm the diagnosis. A mallein test for delayed hypersensitivity is performed by intrapalpebral inoculation with mallein, a secreted glycoprotein of B mallei found in culture supernatant. Infected hypersensitive horses develop purulent conjunctivitis and swelling of the eyelids within 24 hours of inoculation. In most areas of the world, the mallein test is superseded by serological testing.
WOAH recommends using the complement fixation test (CFT) to screen for infection; however, this test can produce false-positive results (because of its variable specificity), as well as false-negative results in latently infected animals. Competitive ELISA is more sensitive than the CFT and can detect B mallei antibodies as early as 3 days after infection. Both competitive ELISA and Western blot have higher specificity and are indicated when false-positive CFT results are suspected. Real-time PCR assay can be used for specific clinical case identification but has not been fully validated for this purpose.
Prevention, Control, and Treatment of Glanders in Horses and Other Equids
Prevention and control: detection and elimination of confirmed cases
Treatment: contraindicated
There is no vaccine for glanders. Protective immunity involves T-cell responses elicited by live, attenuated bacteria. Prevention and control depend on early detection and elimination of affected animals (euthanasia and safe disposal of the carcass), as well as complete quarantine and rigorous disinfection.
Successful control also depends on establishing awareness of disease among horse and donkey owners in remote areas, where underreporting, lack of diagnostic surveillance, and minimal funding to support animal culling and owner compensation are continuing challenges.
Treatment of glanders is generally prohibited and contraindicated because of the zoonotic potential and because treatment does not reliably produce a bacteriological cure. Longterm administration of doxycycline or combination trimethoprim plus sulfadiazine may be effective in preventing glanders or may result in survival and development of chronic or latent infection (1).
Zoonotic Risk of Glanders in Horses and Other Equids
Humans can contract glanders through direct contact with infected animals or their bodily fluids, by direct contact with contaminated materials, or via aerosol transmission of B mallei. In humans, infection can result in severe skin ulcers, fever, muscle pain, chest pain, and, if untreated, death.
The following personal protective equipment should be worn around or when handling infected animals, tissues, or fluids:
disposable gloves
surgical mask or N95 respirator
goggles or face shield
protective clothing, such as disposable gowns or coveralls, which should be properly disposed of after use
Carcasses of affected animals should be disposed of as follows to minimize zoonotic risk:
The carcass should be handled with care, to avoid contact with fluids, and placed in a strong, leakproof, plastic bag. Double-bagging is recommended.
The environment and the outer surface of the bag must be thoroughly cleaned to remove organic material and then disinfected with an appropriate agent. Removal of organic material is crucial to ensure effective disinfection. Manufacturer-recommended concentration and contact times for each disinfectant must be followed to achieve optimal results.
The carcass should be either incinerated or buried (at least 2 meters [approximately 6.5 feet] deep) in a designated biosecure landfill. The disposal method must comply with local regulations to prevent environmental contamination.
B mallei is generally susceptible to a variety of disinfectants; however, its resistance can vary depending on the environment and the presence of organic matter. When manufacturer's instructions are followed and surfaces are thoroughly cleaned before disinfecting, the following agents are generally effective against B mallei:
sodium hypochlorite (bleach): effective at concentrations of 0.5−1% active chlorine
ethanol-based disinfectants: effective for surfaces but possibly insufficient for heavily contaminated areas or in the presence of organic matter
formaldehyde: highly effective but requires careful handling because of toxic and irritant properties
Key Points
Glanders, a reemerging, zoonotic, contagious, and often fatal disease of horses and other equids, is caused by infection with Burkholderia mallei bacteria.
Control depends on detection, isolation, and culling of affected animals.
Treatment might not eliminate infection and is contraindicated due to potential zoonosis.
Because glanders is zoonotic, precautions must be taken to ensure public safety.
For More Information
World Organisation for Animal Health. Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. 13th ed. 2024.
European Food Safety Authority. Glanders: geographical distribution.
Verdegaal EJMM. Glanders. In: Lavoie JP, ed. Blackwell's Five-Minute Veterinary Consult: Equine. 3rd ed. Wiley;2019:338.
Also see pet owner content regarding glanders in cats, dogs, and horses.
References
Saqib M, Muhammad G, Naureen A, et al. Effectiveness of an antimicrobial treatment scheme in a confined glanders outbreak. BMC Vet Res. 2012;8:214. doi:10.1186/1746-6148-8-214
