Glanders is one of the most dangerous infectious diseases affecting odd-toed ungulates, especially horses, donkeys, and mules. The disease not only causes serious health problems in animals but can also be transmitted to humans through contact with secretions, pus, or lesions from infected animals.
Early recognition of the causes, transmission routes, clinical signs, and lesions of glanders plays an important role in disease prevention, source control, and reducing the risk of pathogen spread within the herd. In Part 1 of this article, the Fivevet Field Technical Department will provide livestock farmers with an overview of glanders, including its causes, epidemiological characteristics, and common clinical manifestations.
What is glanders?
1. What is glanders?
Glanders, also known as Malleus, is a dangerous infectious disease caused by the bacterium Burkholderia mallei. The disease mainly affects equines, especially horses, donkeys, mules, and some other susceptible animals. It can also be transmitted to humans through contact with secretions, pus, or lesions from infected animals. Therefore, animals suspected of having glanders should be isolated immediately, and self-treatment or necropsy should be avoided. The case should be reported to veterinary authorities for examination using appropriate methods such as the Mallein test, serological tests, or bacteriological examinations.
2. Causes of Glanders
Glanders is caused by the bacterium Burkholderia mallei. It is a Gram-negative, rod-shaped bacterium without flagella and has low resistance in the external environment.
The bacterium can survive for only a few days in dried secretions from infected animals. However, under high-humidity conditions, the pathogen may remain viable for several weeks. It is rapidly destroyed at temperatures around 60°C and by common disinfectants.
Main Routes of Transmission of Glanders
3. Epidemiology of Glanders
Animals infected with glanders but not yet showing obvious clinical signs are dangerous sources of infection, silently spreading the pathogen within the herd. This allows the disease to spread before farmers recognize any abnormal symptoms.
The pathogen mainly enters the body through the digestive tract, especially via contaminated feed and drinking water. Therefore, shared feeding and watering systems in areas where many equines are raised can facilitate rapid outbreaks and widespread transmission.
After entering the body, the bacteria persist in the mucosa of the pharyngeal region and throat. From there, they spread throughout the body, mainly to the lungs, nasal mucosa, and skin. At sites where the pathogen localizes, small nodules begin to form. Over time, these nodules rupture, dry out, slough off, and leave scars, particularly on the skin.
4. Clinical Signs of Glanders
Based on the sites affected and the pathological changes observed, glanders can be classified into several different forms. Each form has its own clinical manifestations, but they commonly involve lesions in the nasal cavity, lungs, skin, and lymphatic system.
Acute Form of Glanders
The acute form is commonly seen in donkeys and horses. It has a very short incubation period of about 2–4 days, and the disease progresses rapidly within 2–3 days.
Affected animals may show the following signs:
- Rhinitis with greenish-yellow nasal discharge or blood-stained discharge.
- Rapidly progressing rhinitis with the formation of pseudomembranes in the nasal cavity.
- Small nodules, abscesses, and ulcerative lesions on the nasal mucosa.
- Bilateral enlargement of the nasal lymph nodes, forming suppurative abscesses that may rupture through the skin.
Chronic Form of Glanders
The chronic form commonly occurs in horses and may persist for several years. In many cases, clinical signs are not obvious, making the disease difficult to detect through external observation alone.
Animals with the chronic form may show the following signs:
- Intermittent high fever or irregular fever.
- Increased respiratory rate.
- Swelling of the limb joints.
- Chronic lymphadenitis.
- Weight loss and progressive emaciation.
Some cases are only detected through the Mallein test or other immunodiagnostic methods.
Nasal Form of Glanders
The nasal form usually begins with rhinitis. Both nostrils may contain large amounts of greenish-yellow mucus mixed with necrotic tissue and blood.
- When coughing or snorting, infected animals may expel large amounts of mucus from the nostrils. Yellowish-gray nodules develop on the nasal mucosa, which later ulcerate and form suppurative abscesses.
- The ulcers gradually enlarge and merge into larger ulcerative lesions. If healing occurs, scars may remain on the nasal mucosa and the nasal septum. Swelling of the nostrils and lips may also occur, accompanied by ulcerative lesions.
- In both acute and chronic forms, the lymph nodes near the ulcerative lesions are commonly inflamed.
- Ulcerative nodules may also appear on the skin, becoming thickened, yellowish, and exudative.
The pulmonary form
- The pulmonary form usually develops slowly over several months. Affected animals may show reduced weight gain, progressively worsening respiratory distress, coughing, and wheezing, especially if the larynx is inflamed.
- Subsequently, lesions may also appear around the nasal area and on the skin. Due to its slow progression, the pulmonary form should be carefully monitored to avoid confusion with other respiratory diseases.
The cutaneous form
The cutaneous form, also known as Farcy, is characterized by the appearance of multiple skin nodules measuring approximately 1–3 cm in diameter, commonly found on the limbs, chest, and abdomen.
- These nodules may rupture and ulcerate, discharging exudate onto the skin surface, resulting in chronic ulcers and the formation of firm skin nodules. Additional nodules and ulcerative lesions may develop around the lymph nodes, producing lesions that resemble those of contagious lymphadenitis.
- The subcutaneous tissues surrounding the ulcerative lesions are often swollen and edematous, with the swelling spreading extensively, particularly in the hind limbs.
Clinical Signs of Glanders
5. Pathological Lesions of Glanders
Glanders can cause lesions in multiple organs throughout the body. In the lungs, the disease leads to the formation of pulmonary nodules. Over time, these nodules may become suppurative and encapsulated.
The lung surface may exhibit focal areas of inflammation accompanied by mucous exudate. In addition to the lungs, nodules may also develop in abdominal organs, the reproductive organs, bones, and lymph nodes. These nodules can likewise become inflamed and contain pus.
In the next section, this article will discuss the diagnostic methods for glanders, disease prevention measures, management of affected animals, and important considerations when animals are suspected of being infected.
This article was prepared by the Field Technical Department of Central Veterinary Medicine JSC No.5 (Fivevet).
References:
https://khoathuy.vnua.edu.vn/phong-ngua-benh-ty-thu-o-ngua.html
Nguyen Ba Hien et al.
Veterinary Infectious Diseases Textbook. Agricultural Academy Publishing House.
Frequently Asked Questions (FAQs)
1. What is glanders?
Glanders is a serious infectious disease caused by the bacterium Burkholderia mallei. It primarily affects equids such as horses, donkeys, and mules and can also be transmitted to humans through contact with secretions, pus, or lesions from infected animals.
2. Which animals are commonly affected by glanders?
Glanders most commonly occurs in equids, particularly horses, donkeys, and mules. Some other susceptible animal species may also become infected, although such cases are less common.
3. What causes glanders?
Glanders is caused by the bacterium Burkholderia mallei. This organism has relatively low resistance in the environment and can be readily destroyed by temperatures around 60°C and by commonly used disinfectants.
4. How is glanders transmitted?
The pathogen can enter the body through the digestive tract, mainly via feed or drinking water contaminated with the bacteria. Shared feed and water troughs in facilities housing multiple equids can increase the risk of disease transmission.
5. What are the common clinical signs of glanders?
Common clinical signs include rhinitis, greenish-yellow or blood-tinged nasal discharge, ulcerative lesions on the nasal mucosa, enlargement of lymph nodes, coughing, respiratory distress, intermittent fever, weight loss, and progressive emaciation.
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