333Chapter 36 Glanders

36 

GlandersAnthony N.B. Kettle and Paul L. Nicoletti*

C H A P T E R 

Glanders is one of the oldest recorded diseases of equids with zoonotic potential known since ancient times. Disease symp-toms were recorded by Hippocrates in 425 BC and was given the name “melis” by Aristotle in 350 BC.1,2 The common etiology of these diseases was first demonstrated by Viborg at the end of the eighteenth century.2 The etiologic agent, now known as Burkholderia mallei, was isolated in 1882 by Loeffler and Schütz from the liver and spleen of an infected horse.1,3 The mallein test for diagnosis of glanders was developed in 1890.4

By the second half of the nineteenth century, glanders was widespread in horses in North America, and a major epidemic of disease occurred in association with movement of horses during and after the Civil War.1,4,5 Burkholderia mallei was reportedly used as a biologic warfare agent in World Wars I and II and the Russian invasion of Afghanistan.6 Burkholderia mallei

is now regarded as a select agent (category B, U.S. Centers for Disease Control and Prevention) and all experimental work must be carried out in a Level 3 Biosafety facility.7,8 Disease caused by B. mallei must be reported to the World Organization for Animal Health (formerly the Office International des Epi-zooties [OIE]) in Paris.

Etiology

Burkholderia mallei (formerly Pseudomonas, Bacillus, Pfeifferella, Loefflerella, Malleomyces, Actinobacillus, Corynebacterium, and Mycobacterium) is a short, rod-shaped, gram-negative, aerobic, facultative intracellular, nonmotile, and non–spore-forming bac-terium. The organism survives outside the host for varying periods of time, depending on many factors. Virulence factors of B. mallei include capsular polysaccharide, lipopolysaccharide,

*The authors acknowledge and appreciate the original contributions of these authors, whose work has been incorporated into this chapter.

334 Section 3 Bacterial and Rickettsial Diseases

by subclinically infected horses. Poor sanitation, crowding, and immunosuppression from parasitism are considered risk factors. The incubation period varies from a few days to many months. The disease has been the target of eradication efforts for many decades because of its clinical effects in equids and its public health implications. The increasing number of outbreaks in recent years led to the classification of glanders as a reemerging disease.

Clinical Findings

Historically, glanders is described as either acute or chronic, but clinically it may be difficult to distinguish between the two forms. It is perhaps better to regard chronic glanders as a pro-gressive disease comprised of acute episodes occasionally inter-spersed with periods of latency. The host factors determining the course of the infection are unknown. Donkeys are most likely to die from acute disease within 7 to 10 days, whereas horses may either die rapidly or live for several years with chronic abscessation.

Acute glanders is characterized by bronchopneumonia and septicemia with a moderate to high fever, depression, and rapid weight loss. Frequently, highly infectious mucopurulent to hem-orrhagic nasal discharge forms crusts on the external nares. Submaxillary lymph nodes are frequently swollen, painless, and seldom rupture.

Chronic glanders is typically described as one of three forms: cutaneous (farcy), nasal, or pulmonary, although in practice there is much overlap between the three forms.

In the cutaneous form, nodules develop into crater-shaped ulcers discharging a thick yellow exudate (Fig. 36-1, A) and generally track the lymphatic vessels to regional lymph nodes. The lymph vessels become swollen and corded with nodules appearing at intervals en route (Fig. 36-1, B). The cutaneous lesions may appear anywhere on the body, but typically the limbs and especially the hindlimb are more frequently affected.

The nasal form is characterized by frequent snorts to clear the nasal passages as nodules form on the nasal septum and erupt to discharge a thick tenacious yellow exudate (Fig. 36-2).

Figure 36-1  A, Crater-shaped ulcers with exudate. B, Swollen cutaneous lymphatics with nodules. (Courtesy Dr. U. Wernery, Central Veterinary Research Laboratory, Dubai, UAE.)

A B

and type III and VI secretion pathways.9-12 Capsular polysac-charide is essential for virulence in hamsters and mice.12 An acapsular mutant of B. mallei failed to induce disease in experi-mentally infected horses.13 In addition, a complex quorum-sensing network and a two-component transcriptional regulatory system are required for maximal virulence in hamsters.14

Epidemiology and Pathogenesis

Although occasional cases of glanders occur in cats, dogs, goats, and sheep, the principal hosts are horses, donkeys, and mules. Recently, natural infection has been reported in camels as well.15 Carnivores, such as lions, may be infected from ingestion of contaminated meat as occurred in the Tehran Zoo in 2010. Mice and guinea pigs can be experimentally infected. Both acute and chronic forms of the disease are found; horses typi-cally are chronically infected, whereas donkeys and mules are more likely to develop the acute form. Chronically infected equids are the only known reservoir for B. mallei. Human infec-tions can occur by aerosol transmission from infected animals and are frequently fatal if untreated.

Glanders is restricted geographically to Eastern Europe, Asia, North Africa, South America, and the Middle East. It is consid-ered endemic in Iraq, Turkey, Pakistan, India, Mongolia, and China,16-23 where reported outbreaks appear to be increasing in the last 10 to 20 years. Reports of recent outbreaks in Brazil, Bahrain, Lebanon, and Kuwait have appeared in the veterinary literature22,23 and on the OIE Website. Glanders has been eradi-cated from Europe, Australia, and North America by a rigorous policy of culling animals that are positive by complement fixa-tion test (CFT), serum agglutination test, or the mallein test. An accidental human infection occurred in a laboratory worker in 2000,24 but there have been no naturally occurring cases of glanders in North America for more than 60 years. The last case in animals in the United States was in 1942.

Burkholderia mallei is a niche-specific derivative of Burkhold-eria pseudomallei.25,26 The primary route of infection in horses is through the ingestion of feed or water contaminated by the nasal secretions of infected horses.1 The disease can be spread

335Chapter 36 Glanders

Figure 36-2  Nasal exudate  in horse with glanders.  (Courtesy Dr U. Wernery, Central Veterinary Research Laboratory, Dubai, UAE.)

Figure 36-3  Granulomas  and  ulcers  (stellate  scar)  in  nasal  septum  of  horse with glanders. (Courtesy Dr U. Wernery, Central Veterinary Research Laboratory, Dubai, UAE.)

The nasal discharge may become hemorrhagic as nodules rupture, leaving large ulcers that heal forming stellate scars (Fig. 36-3). There is a regional lymphadenopathy, and the glottis may become swollen, which leads to dyspnea.

The pulmonary form is an extension of the nasal form to the lower respiratory tract with the formation of round, grayish, firm nodules within the lungs (Fig. 36-4). Similar abscesses may be found on the liver and spleen (Fig. 36-5), and occasionally, orchitis may occur in stallions (Fig. 36-6).1,16,27

Diagnosis

Glanders must be differentiated from other chronic infections of the upper respiratory tract, including strangles (Streptococcus equi subsp. equi), ulcerative lymphangitis (Corynebacterium pseudotuberculosis), pseudotuberculosis (Yersinia pseudotubercu-losis), and sporotrichosis (Sporotrichum spp.), and from epizo-otic lymphangitis (Histoplasma farciminosum). In humans, glanders also needs to be differentiated from melioidosis (Burk-holderia pseudomallei).28

The test for glanders listed in the OIE Terrestrial Manual in 2012 for international trade is the CFT. Historically, the mallein test (Fig. 36-7) was used to eradicate glanders from North

Figure 36-4  Pulmonary granulomas in lungs of horse with glanders. (Courtesy Dr U. Wernery, Central Veterinary Research Laboratory, Dubai, UAE.)

Figure 36-5  Abscesses  on  spleen  of  horse  with  glanders.  (Courtesy Dr U. Wernery, Central Veterinary Research Laboratory, Dubai, UAE.)

Figure 36-6  Swollen sheath in horse with orchitis caused by glanders. 

America and Britain at the turn of the twentieth century since the CFT was not available for glanders until 1913. Early reports indicated the CFT was less sensitive than the mallein test.

Mallein is a heat-treated solution of water-soluble proteins, primarily lipopolysaccharide (LPS), extracted from B. mallei.29 The intradermal-palpebral application of the test is acknowl-edged as the most sensitive, reliable, and specific of the mallein

336 Section 3 Bacterial and Rickettsial Diseases

susceptibility patterns of 15 isolates of B. mallei to 35 antimi-crobial agents.36 The most effective drugs in vitro included imipenem, ceftazidime, ciprofloxacin, piperacillin, doxycycline, and aminoglycosides. There were no obvious differences in sus-ceptibility patterns among human, animal, and environmental isolates. Recently, experimental work has been done with granu-lysin and silver carbine compounds.37 The availability of several B. mallei genome sequences has greatly facilitated the develop-ment of new therapeutics; however, much work remains to be done to determine a suitable treatment regimen for horses. The difficulty with treatment in horses is in determining whether the infection has been eliminated.

Prevention

Glanders has been successfully eliminated from most countries through rigorous slaughter of animals with a positive mallein test. Quarantine of in-contact animals and pretesting of horses for movement are necessary components of disease control. A wide variety of national and international regulations exist, and glanders is a reportable disease for the OIE and many countries.

There is no vaccine for prevention of glanders in animals. Research efforts currently are focused on development of a vaccine for people in case the organism becomes an instrument of bioterrorism. A recent report highlights promising results for a vaccine using T-helper epitopes,38 and a series of protective antigens have been identified by genome analysis that may also be useful in the development of a vaccine.39

Public Health Considerations

Glanders is a rare but serious zoonotic disease. Most human cases are ultimately traced to direct contact with B. mallei through exposure to infected animals or laboratory exposure to the organism.24,27,41 The organism often enters via cutaneous exposure through the hands or arms. The incubation period is estimated to be a few days to several weeks but can be much longer. Local suppuration and regional lymphadenopathy with fever and lethargy are often the first symptoms.24 Dissemination of infection occurs 1 to 4 weeks after lymph node involvement becomes apparent. Systemic effects may include abscesses in the liver, spleen, lungs, pleura, subcutis, and muscles.24,27,40,41 Mortality in acutely affected people with untreated disease approaches 95% within 3 weeks. As previously mentioned, several antibiotics have reliable activity against B. mallei24,33-36 and are usually used in combination against B. mallei infections. In a recent report of glanders in a laboratory worker, treatment with imipenem and doxycycline for 2 weeks, followed by azithromycin and doxycycline for 6 months, was successful (in vitro susceptibility testing did not support the use of azithro-mycin).24,27 Glanders in human patients may be difficult to diagnose because of a lack of awareness and rarity of human disease.27

The complete reference list is available online at www. expertconsult.com.

tests for glanders. The immunologic basis for the test is primar-ily a stimulation of memory T cells. Anergy may result in a false-negative reaction. False-positive reactions may also occur. In negative horses, mallein may induce antibodies that are detectable for up to 19 weeks after injection.30

The CFT is currently the test used for international trade, but a number of nonspecific false-positive results occur.30 These false positives are thought to derive at least in part from the use of crude cell-antigen preparations and also from cross-reactions with other bacteria.

Recently, a Western immunoblot technique has been pro-posed (but has yet to be validated) for resolving the false posi-tives found in the CFT for use in areas with low glanders prevalence.31 Several other serologic tests and diagnostic tech-niques are now available for glanders diagnosis, including polymerase chain reaction (PCR), agglutination, indirect hem-agglutination, enzyme-linked immunosorbent assay (ELISA), counter immunoelectrophoresis, Rose-Bengal staining, and competitive ELISA (cELISA).32 Culture and immunohisto-chemical staining for bacterial antigen may be used. Although rarely used, guinea pigs are highly susceptible, and an acute purulent orchitis occurs in a few days after inoculation of mate-rial (Strauss test). A lack of sensitivity of this procedure and culture has been reported.17 Recent advances in our under-standing of B. mallei and the increasing availability of molecular diagnostic tools may soon result in a new generation of more sensitive and specific diagnostic tests for glanders in horses.32

Therapy

Euthanasia and slaughter of equids with glanders are strongly recommended and may be mandatory in some countries. Although there are relatively few studies of antimicrobial sus-ceptibility patterns of B. mallei, it appears that this organism is resistant to many antimicrobial drugs, including β-lactam antibiotics.33-36 A recent study examined the antimicrobial

Figure 36-7  Performing the intradermal mallein test. (Courtesy Dr U. Wernery, Central Veterinary Research Laboratory, Dubai, UAE.)

336.e1Chapter 36 Glanders

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