Equine Glanders Study Guide

Overview and Clinical Importance

Glanders (farcy) is a highly contagious and often fatal zoonotic disease caused by

Burkholderia mallei, a gram-negative, facultative intracellular bacterium. The disease primarily affects equids (horses, mules, and donkeys) and is notifiable to the World Organisation for Animal Health (WOAH).

Although glanders has been eradicated from North America, Australia, and most of Europe, it remains endemic in parts of Asia, Africa, the Middle East, and South America. The disease is a significant concern for global equine movement and poses serious public health and bioterrorism risks.

Etiology and Organism Characteristics

Burkholderia mallei

Taxonomy: Genus Burkholderia, closely related to B. pseudomallei (melioidosis)

Morphology: Gram-negative, non-motile, non-sporeforming, facultative intracellular rod

Growth characteristics: Obligate aerobic bacterium; grows on blood agar at 37°C

Environmental survival: Limited survival outside host (1-2 months maximum); susceptible to heat, light, and disinfectants

Epidemiology and Global Distribution

Current Endemic Areas

Endemic regions: Asia (India, Pakistan, Bangladesh, Mongolia, China), Middle East (Iran, Iraq, UAE, Bahrain), parts of Africa, and South America (Brazil)

Eradicated regions: North America, Australia, most of Europe through systematic testing and culling programs

India has experienced significant re-emergence since 2006, with Uttar Pradesh identified as a hotspot zone. Trading of equids from endemic areas has been the primary mechanism for geographic spread.

Global Status Summary

Transmission and Pathogenesis

Routes of Transmission

Primary routes:

• Ingestion of contaminated feed or water (most common)
• Inhalation of aerosolized bacteria
• Penetration through mucous membranes (nasal, oral, conjunctival)
• Skin abrasions and wounds

Sources of infection: Nasal discharge, pus from cutaneous lesions, contaminated equipment, feed, and water. Asymptomatic carriers pose significant transmission risks.

Pathogenesis

Following entry,

B. mallei exhibits tropism for the respiratory tract, lymphatic system, and skin. The organism is facultatively intracellular and can survive within macrophages, enabling chronic infection and immune evasion.

Key virulence factors:

• Polysaccharide capsule enhancing environmental survival
• Type III and Type VI secretion systems
• Lipopolysaccharide endotoxin
• Ability to survive intracellularly in macrophages

Clinical Manifestations

Glanders presents in three primary forms that may occur simultaneously:

pulmonary (most common), nasal, and cutaneous (farcy). The disease course can be acute, chronic, or latent, with significant species variations.

Incubation period: 3 days to 2 weeks for acute forms; months to years for chronic forms

Clinical Forms and Presentations

Pulmonary Form

Most common presentation: Pneumonia with nodular lesions progressing to abscesses

Clinical signs:

• Cough (initially dry, progressing to productive)
• Dyspnea and exercise intolerance
• Fever (intermittent in chronic cases)
• Progressive weight loss
• Enlarged submandibular lymph nodes

Radiographic findings: Bilateral bronchopneumonia, miliary nodules, lung abscesses. May reveal segmental consolidation or pleural effusion.

Nasal Form

Pathognomonic lesions: Nodules on nasal septum and turbinates that ulcerate to form characteristic deep ulcers with raised, irregular borders

Clinical progression:

• Initial: Unilateral or bilateral nasal discharge (serous to mucopurulent)
• Progressive: Blood-tinged discharge (epistaxis)
• Advanced: Stellate scars formation after ulcer healing
• Chronic: Honeycomb appearance of nasal mucosa

Cutaneous Form (Farcy)

Distribution: Nodules appear along lymphatic vessels, particularly on limbs, abdomen, and neck

Characteristic lesions:

• Subcutaneous nodules (1-2 cm diameter)
• Lymphangitis with cord-like swelling
• Ulceration producing sticky, honey-like discharge
• Regional lymphadenopathy

Diagnosis

Diagnosis of glanders relies on a combination of clinical evaluation, serological testing, bacteriological culture, and molecular methods. Due to the high biosafety risk, all laboratory work must be conducted in BSL-3 facilities.

Clinical Diagnosis

Presumptive diagnosis: Based on characteristic clinical signs, history of exposure, and epidemiological factors

Key diagnostic indicators:

• Chronic progressive respiratory disease in equids
• Characteristic nasal ulcers with stellate scarring
• Cutaneous nodules along lymphatics (farcy)
• History of contact with equids from endemic areas

Mallein Test

Principle: Delayed-type hypersensitivity test using mallein (purified glycoprotein from B. mallei culture supernatant)

Procedure: Intrapalpebral injection of 0.1 mL mallein into lower eyelid

Positive reaction: Purulent conjunctivitis and marked eyelid swelling within 24-48 hours

Limitations: Cannot differentiate naturally infected from malleinized animals; false positives possible

Serological Testing

Bacteriological Culture

Sample collection: Nasal swabs, pus from cutaneous lesions, tissue samples from necropsied animals

Culture media: Glycerol blood agar, Burkholderia cepacia agar with selective agents

Growth characteristics: Small, translucent colonies after 2-4 days at 37°C; characteristic viscous consistency

Limitations: Low sensitivity in chronic cases; requires BSL-3 facilities; time-consuming

Molecular Diagnostics

PCR targets: fliP gene, bimAma gene, TTS1 gene, and species-specific sequences

Advantages: High sensitivity and specificity; rapid results; can detect low bacterial loads

Real-time PCR: Quantitative detection with rapid turnaround; most suitable for outbreak investigations

Differential Diagnosis

Primary differentials:

• Strangles (Streptococcus equi equi) - typically younger horses, lymph node abscesses
• Melioidosis (B. pseudomallei) - similar presentation, geographic distribution key
• Rhodococcus pneumonia - common in foals, different epidemiology
• Equine infectious anemia - different chronicity pattern
• Tuberculosis - extremely rare in horses
• Epizootic lymphangitis (Histoplasma farciminosum) - geographic distribution

Treatment and Control Measures

Treatment Protocols

Regulatory restriction: Treatment of equine glanders is

prohibited by current regulations in most countries to prevent development of antibiotic resistance and ensure complete eradication.

Experimental treatment protocols (for human cases or research purposes):

Control and Eradication Strategies

Core control principles:

• Early detection through surveillance
• Immediate isolation of suspected cases
• Mandatory reporting to authorities
• Humane euthanasia of positive animals
• Safe carcass disposal (burial or incineration)
• Thorough disinfection of premises
• Movement restrictions and quarantine
• Compensation programs for affected owners

Import/export requirements:

• Pre-import quarantine testing (CFT, ELISA)
• Health certificates from veterinary authorities
• Post-arrival quarantine periods
• Movement tracking and documentation

Disinfection and Environmental Management

Environmental survival: B. mallei survives 1-2 months outside the host under favorable conditions (humid, cool environments)

Effective disinfectants:

• 1% sodium hypochlorite (bleach)
• 70% ethanol
• Quaternary ammonium compounds
• Phenolic disinfectants
• Heat treatment (susceptible to temperatures greater than 60°C)

Public Health and Zoonotic Transmission

Human Glanders

Transmission to humans: Usually occurs through direct contact with infected animals or contaminated materials

High-risk occupations:

• Veterinarians and veterinary students
• Laboratory personnel
• Horse handlers and caretakers
• Slaughterhouse workers
• Military personnel in endemic areas

Clinical forms in humans:

• Localized cutaneous form (most common)
• Pulmonary form (inhalation exposure)
• Septicemic form (highest mortality)
• Chronic disseminated form

Case fatality rate: 50% with appropriate treatment; up to 95% if untreated

Bioterrorism Potential

Category B bioterrorism agent: Classified by CDC due to moderate dissemination ease and potential for causing significant morbidity

Bioweapon characteristics:

• Historical use in World War I (German biological warfare program)
• Low infectious dose required
• High mortality rate
• Potential for aerosol dissemination
• No available vaccine
• Difficult clinical recognition leading to delayed treatment

Laboratory Safety and Biosafety

Biosafety level requirement: BSL-3 (Biosafety Level 3) for all work with live B. mallei

Personal protective equipment:

• Full-face respirator or powered air-purifying respirator
• Double gloves
• Disposable protective clothing
• Eye protection