Glanders & Melioidosis
Glanders is a bacterial disease caused by Burkholderia mallei. The disease primarily affects horses, donkeys, and mules, although a number of other mammals are susceptible to infection (CDC 2012: Glanders).
In humans, B mallei causes a febrile illness with four characteristic clinical presentations (localized, pulmonary, septicemic, and chronic). Most naturally occurring human infections have been related to contact with horses. Glanders has been eradicated in much of the world, including the United States, where the last naturally occurring equine and human cases were identified in 1942 and 1934, respectively (CDC 2012: Glanders, Gregory 2007). Since World War II, the only human cases in the United States have been laboratory acquired (CDC 2000, Gregory 2007, Srinivasan 2001). However, B mallei has the potential for use as a biological weapon and so remains of interest (Gilad 2007).
Melioidosis is a bacterial disease caused by the saprophyte B pseudomallei; it affects humans and many species of animals (CDC 2012: Melioidosis). Human melioidosis is a febrile illness with great clinical diversity, ranging from asymptomatic infection to fulminant septic shock with multiple organ abscesses (Currie 2010). The disease is endemic in tropical and subtropical regions located between 20ºN and 20ºS latitude; the greatest numbers of cases are reported from Southeast Asia and northern Australia. In the United States, only sporadic nonindigenous cases of melioidosis have been observed, along with one laboratory-acquired infection (CDC 2012: Melioidosis, Schlech 1981, Vietri 2007). B pseudomallei also is regarded as a bioterrorism threat (Gilad 2007).
Burkholderia is a genus that contains more than 30 species, but only three are recognized as human or animal pathogens (Gilligan 2003, Wiersinga 2006):
- B mallei (the causative agent of glanders)
- B pseudomallei (the causative agent of melioidosis)
- B cepacia complex (at least nine closely related genomic species that usually cause nosocomial or opportunistic infections in patients with chronic granulomatous disease or cystic fibrosis)
Other Burkholderia species generally are considered avirulent, although human infections with these organisms are identified occasionally. In one case, for example, B thailandensis caused pneumonia and septicemia in a 2-year-old boy who had been submerged under water after a car accident in northeastern Texas (Glass 2006).
B mallei is the most easily identified member of the genus, because the organism is nonmotile, whereas all other species in the genus are motile. B pseudomallei is biochemically similar to B mallei, although it has a characteristic musty, earthy odor that is apparent upon opening the culture plate. The two organisms have the characteristics described in the table Appearance and Biochemical Properties of Burkholderia mallei and B pseudomallei in the "Laboratory Diagnosis" section of this overview and listed below (ASM 2013, Gilligan 2003):
- Gram-negative rod
- 1 to 5 microns long and 0.5 to 1 microns wide
- B mallei is nonmotile; B pseudomallei and other members of the genus possess two or more flagella
- B pseudomallei is oxidase-positive; B mallei may or may not be oxidase-positive
- Possesses arginine dihydrolase activity
- Reduces nitrate to nitrite
- Oxidizes glucose but not sucrose or maltose
B mallei and B pseudomallei are susceptible to a number of disinfectants, including 1% sodium hypochlorite, 70% ethanol, glutaraldehyde, and others (although the required concentrations and contact times may vary by organism) (CFSPH 2007: Glanders; CFSPH 2007: Melioidosis).
The genomes of B mallei and B pseudomallei have been sequenced and analyzed (NCBI). The strain of B mallei that was first sequenced is ATCC 23344, a strain originally isolated in 1944 from postmortem samples of a Chinese soldier who died of a glanders-melioidosis–type infection in Burma (Waag 2005).
- The B mallei genome consists of about 5.8 megabases (Mb) on two circular chromosomes, one of 3.5 Mb and the other of about 2.3 Mb (Nierman 2004).
- Sequence data and multilocus sequence typing suggest that B mallei evolved in animals from the environmental pathogen B pseudomallei; this evolution most likely resulted in a reduced capacity for environmental survival coincident with an increased advantage for survival in the mammalian host (Currie 2010, Larsen 2009, Nierman 2004).
- B pseudomallei has a larger genome than that of B mallei and consists of 7.2 Mb on two chromosomes (4.07 Mb and 3.17 Mb) (Holden 2004).
- The lipopolysaccharides of B pseudomallei can be used to characterize the geographic location of origin. Type A is found in Southeast Asia, and type B is found in Australia (Tuanyok 2012).
Despite being unique organisms, B mallei and B pseudomallei have many similarities and may be considered together in the context of bioterrorism (Gilad 2007).
Work is ongoing to identify and characterize the virulence factors involved in the pathogenesis of B mallei and B pseudomallei infections. The capsule, protein secretion, and quorum sensing systems have been suggested as essential virulence determinants. The inability to fully characterize B mallei and B pseudomallei virulence factors and the lack of understanding of their basic mechanisms of pathogenesis have impeded the development of medical countermeasures (Galyov 2010, Larsen 2009).
The characteristic findings of glanders include purulent oropharyngeal mucositis and widespread abscesses involving multiple organs, notably the lungs, liver, and spleen (Srinivasan 2001). Computed tomographic appearance of hepatic and splenic involvement can mimic echinococcal or amebic infection, so a high index of suspicion is essential in making the diagnosis (Georgiades 2001).
Infection occurs following percutaneous inoculation, inhalation, or ingestion. Disease severity appears to depend on the route of infection (with inhalational exposure leading to the most severe disease), bacterial load, virulence of the specific infecting strain, and host factors (such as diabetes, excessive alcohol intake, chronic pulmonary disease chronic renal disease, and cancer).
B pseudomallei is a facultative intracellular pathogen that can invade and replicate inside various cells, including macrophages, polymorphonuclear leukocytes, and some epithelial cell lines (Curry 2010); this feature is critical for pathogenesis (Wiersinga 2012). Once inside the cell, the bacteria can form cell membrane protrusions and can spread directly from cell to cell.
B pseudomallei can stimulate the release of proinflammatory cytokines, which activate the coagulation system in severe melioidosis and can lead to sepsis syndrome.
B mallei causes a highly communicable disease in horses, mules, and donkeys. Donkeys tend to develop an acute form of the disease, horses are prone to develop a more chronic form, and mules are intermediate in susceptibility (Gilbert 2008). These animals are the primary reservoirs for the organism; humans are an accidental host (Bossi 2004, Gregory 2007, OIE 2010, Rowland 2006, Waag 2005). Several other animal species can contract infection, including the following:
- Domestic cats and members of the cat family living in the wild or in zoos (usually related to consumption of contaminated meat [eg, horsemeat])
- A range of laboratory animals (eg, mice, hamsters, guinea pigs, rabbits, monkeys)
Chicken, swine, and cattle are resistant to infection.
B mallei does not have an environmental reservoir. It is an obligate mammalian pathogen that does not survive well in the environment (Nierman 2004). The organism is inactivated by heat, sunlight, and desiccation. In warm and moist environments, however, B mallei may survive for a few months, and it can survive in room-temperature water for up to 30 days. Under favorable experimental conditions, B mallei was viable for as long as 100 days; in nature, it is unlikely to be viable after 90 days, and most infectivity is lost after a few weeks. B mallei can be destroyed by heating to 55°C for at least 10 minutes or by ultraviolet irradiation (CFSPH 2007: Glanders, Gregory 2007, Khan 2001).
In endemic regions, melioidosis occurs in humans, sheep, goats, horses, swine, cattle, dogs, cats, and other animals (Vietri 2007). Although many animal species are susceptible to melioidosis, they are not thought to serve as a primary reservoir for human disease (Currie 2010). Some researchers have speculated that wild birds may serve as a reservoir for B pseudomallei, and that birds may contribute to the geographic dispersion of the organisms. A study from Australia, however, suggests that wild birds rarely become infected with B pseudomallei and do not appear to spread the organisms to outlying islands (Hampton 2011).
The main reservoir for B pseudomallei is the environment, specifically soil and water in endemic regions (Nierman 2004). In countries where melioidosis is endemic, B pseudomallei is so prevalent that it is a common contaminant found on laboratory cultures (CDC 2012: Melioidosis). B pseudomallei has been identified in native and invasive grasses in northern Australia. The spread of invasive grasses creates new habitats suitable for B pseudomallei and may be important to the spread of melioidosis in that country (Kaestli 2012).
B pseudomallei is capable of surviving in soil and water for months to years as evidenced by laboratory investigations as well as its continued presence in endemic regions. A clinical sample of B pseudomallei remained viable after being stored in water for 16 years (Pumpuang 2011). B pseudomallei is relatively resistant to desiccation, but its resistance to ultraviolet light is less clear. Under more hostile environmental conditions, the organism is capable of existing in a viable, but noncultivable state. B pseudomallei also can enter the cells of protozoa, which may help it survive environmental stresses. The organism can be killed with moist heat of 121°C for at least 15 minutes or dry heat of 160°C to 170°C for at least 60 minutes (CFSPH 2007: Melioidosis).
- The disease is introduced into horse populations by diseased or latently infected animals.
- The major mode of transmission is ingestion of organisms through contact with secretions of infected animals. Transmission appears to be facilitated when animals share feeding troughs or watering facilities.
- Nasal discharges and purulent exudates from draining cutaneous lesions are the main sources of the organisms; however, urine, saliva, tears, and feces apparently can transmit infection.
- Fomites such as tack (ie, articles of harness such as saddles and bridles) have been shown to spread infectious discharges.
- Carnivores can become infected after ingestion of contaminated meat.
One form of the disease (known as "farcy"), is characterized by lesions located on the body or extremities of the animal. Key points regarding transmission of glanders to humans include the following (Bartlett 2004, Dvorak 2008, Waag 2005):
- Human cases traditionally have occurred following occupational contact with horses. Transmission generally involves contact between infectious materials from infected animals that come in contact with mucous membranes or broken skin. Even with close and frequent contact with infected animals, transmission to humans is uncommon (Gregory 2007, Waag 2005). B mallei also may be inhaled via infected aerosols or dust (CDC 2012: Glanders).
- Laboratory-associated infections have been caused by cutaneous and inhalational exposures (CDC 2000, Gregory 2007, Srinivasan 2001).
- Human-to-human transmission has rarely been identified. Cases have included two possible instances of sexual transmission and several infections in family members who cared for patients with glanders (CDC 2012: Glanders, Gregory 2007).
- Epidemics in humans have not been recognized.
- Infections generally are acquired through exposure of mucous membranes or nonintact skin to contaminated soil or water. Additionally, infections have occurred because of aspiration or ingestion of contaminated water, or inhalation of contaminated dust or water droplets.
- Human-to-human transmission is very rare, but cases have occurred via sexual transmission and from melioidosis patients to family caretakers. Vertical transmission from an infected mother to her neonate also has been recorded.
- Contaminated blood-drawing equipment has resulted in nosocomial transmission.
- On a few occasions, laboratory workers have been infected via percutaneous inoculation or via inhalation (Green 1968, Schlech 1981).
- Animal products such as milk can be contaminated when the animal is infected, which could result in human infections in those consuming contaminated milk (Limmathurotsakul 2012).
Overall, B mallei has much greater potential for zoonotic transmission than B pseudomallei, and the risk of laboratory-acquired infection also is greater for B mallei (Currie 2010).
Recognized risk factors for glanders include the following:
- Exposure to horses or other equines in an endemic area (veterinarians; hide and slaughterhouse workers; farriers; farmers; horse, mule, and donkey caretakers; pathologists) (Dvorak 2008, Gregory 2007)
- Work in laboratories where the organisms are handled (USAMRIID 2011)
The most important risk factors for melioidosis are:
- Exposure to contaminated soil or water (particularly untreated drinking water) in an endemic area (especially agricultural workers and military personnel) (Baker 2011, Currie 2010, Vidyalakshmi 2012, Vietri 2007)
- Diabetes, alcoholism, renal disease, chronic lung disease, thalassemia, cancer, and other immunosuppressive conditions increase the risk of disease following exposure (CFSPH 2007: Melioidosis; Currie 2010, Kung 2011, Vidyalakshmi 2012, Vlieghe 2011)
In most endemic regions, melioidosis occurrence is closely associated with rainfall. In Thailand and northern Australia, at least 75% of cases occur during the rainy season (Currie 2010). In a study from Thailand, multivariate analysis determined outdoor exposure to rain to be an independent risk factor for disease (Limmathurotsakul 2013). Above-average rainfall was a key driver in the largest annual increase in human melioidosis cases in northwestern Australia in a 20-year span (Parameswaran 2012). One study demonstrated a strong correlation between exposure to contaminated river water and cases of melioidosis in southern Taiwan (Dai 2012).
A disease compatible with glanders was first recognized in about 400 BC. At one time, glanders was a widespread, severe, and often lethal disease in horses and other equines.
- A major outbreak occurred in South Africa from 1899 to 1902 during the Anglo-Boer War, causing the death of 240,000 horses (Dvorak 2008).
- Glanders was prevalent in the United States in the 1800s, and reportedly 3,000 horses and mules died of glanders in Confederate stables in 1863 (Dvorak 2008).
At the beginning of the 20th century, Canada, the United Kingdom, and the United States implemented glanders control plans that included testing, quarantine, destruction of infected animals, and additional trace-back programs (Srinivasan 2001). Equine glanders was eliminated in Britain (1928), Canada (1938), and the United States (1942), and these measures, along with replacement of the horse as the primary mode of transportation, have been responsible for the dramatic reduction of glanders worldwide. In the United States, the last naturally occurring case of human glanders was recorded in 1934 (Bartlett 2004, Derbyshire 2002, Gregory 2007).
In 1911, cases of a previously unrecognized infectious disease were observed among homeless, debilitated morphine addicts in Burma. The new disease resembled glanders, and the bacillus isolated from postmortem tissue samples was similar to B mallei, although its motility, growth characteristics, and colony morphology were different. The disease became known as "Whitmore's disease" (and later was renamed melioidosis); the bacillus was named B pseudomallei. Subsequently, melioidosis was documented in several countries where it is endemic today (Currie 2010, Tolaney 2009, Vietri 2007).
Melioidosis historically has had an impact on the health of military forces serving in Asia. Cases were reported among Allied and Japanese soldiers during World War II, French troops during the French Indochina War (1946-1954), and US soldiers during the Vietnam War. It is likely that many more cases were undiagnosed. Because cases sometimes surfaced years later in Vietnam veterans, melioidosis has been called the "Vietnam time bomb." Recrudescent melioidosis cases also occurred among World War II veterans. The risk of reactivation of infection is thought to be low (ie, <5% of cases) (Currie 2010, Tolaney 2009, Vietri 2007).
Glanders remains endemic in animals in portions of the Middle East, Asia, Africa, and Central and South America, although very few cases occur each year. In recent decades, outbreaks have been recorded in the following countries (Derbyshire 2002, Scholz 2006).
- India (1992)
- North Africa (1998)
- Iran (1996)
- Iraq (1998)
- Pakistan (1998)
- Brazil (2000)
- United Arab Emirates (2004)
According to the Office International des Epizooties (OIE) World Animal Health Information Database, since the beginning of 2005, sporadic glanders infections have been reported from Brazil, Eritrea, India, Iran, Kuwait, Mongolia, Myanmar, the Philippines, and Russia (OIE: WAHID).
- Hong Kong
- Indian subcontinent
- Northern Australia
Melioidosis also has been observed in the South Pacific, the Middle East, Africa, the Caribbean, and Central and South America. Cases of melioidosis are increasingly being reported from outside the classic endemic regions, and global warming has been suggested as the reason for the expansion of the endemic boundaries of the disease. Travelers returning from regions with melioidosis remain the primary source of cases outside of endemic areas (Salam 2011). Importation of infected animals also has led to the spread of melioidosis and environmental contamination with B pseudomallei (Currie 2010). Limited access to proper antibiotics and improper diagnosis due to a lack of recognition of melioidosis can result in increased mortality, particularly for individuals with pneumonic melioidosis (Rammaert 2011).
The most notable endemic foci are Southeast Asia (particularly Thailand, Malaysia, and Singapore) and northern Australia (CDC 2012: Melioidosis). Thailand has the largest number of reported cases of melioidosis (approximately 2,000 to 3,000 per year) (Currie 2010). In endemic regions, many people asymptomatically seroconvert to B pseudomallei early in life (USAMRIID 2011).
In the US, melioidosis cases typically have occurred among immigrants or recent travelers to endemic areas, or, in one instance, from exposure in a laboratory setting (CDC 2012: Melioidosis). Investigators were unable, however, to identify a source of exposure for a case of melioidosis that occurred in Arizona in 2008 (Stewart 2011).
B mallei and B pseudomallei are considered category B bioterrorism agents (ie, moderate ease of transmission and morbidity with a lower rate of mortality than category A agents) (CDC: Bioterrorism agents/diseases; WHO 2004). Other bacterial category B agents are Chlamydia psittaci (psittacosis), Coxiella burnetii (Q fever), pathogenic Brucella species (brucellosis), Escherichia coli O157:H7 (hemorrhagic colitis), Salmonella species (salmonellosis and typhoid fever), Shigella dysenteriae (shigellosis), and Vibrio cholera (cholera). Several viruses and toxins also are included as category B agents, as are Rickettsia prowazekii (typhus fever) and Cryptosporidium parvum (cryptosporidiosis) (CDC: Bioterrorism agents/diseases).
Inhalation is the most important concern for the use of B mallei and B pseudomallei as biological weapons, because both organisms can be aerosolized. In addition, the following features of B mallei and B pseudomallei contribute to their bioterrorism potential (Gilad 2007, HPA 2008, Pappas 2006, USAMRIID 2011):
- Readily available and relatively easy to cultivate
- Ability to cause infection via inhalation, inoculation, or ingestion
- Relatively low infectious doses
- A high degree of infectivity following aerosol exposure (attack rates in the laboratory setting are close to 50% for B mallei)
- Highly variable incubation periods
- Ability to cause acute, subacute, or chronic disease with a wide spectrum of manifestations; possibility of relapse and reactivation
- Ability to cause rapidly fatal invasive infections
- Rare occurrence in nonendemic countries (so conditions are not well known to clinicians or laboratory personnel, which could lead to a delay in diagnosis and event detection)
- Difficult to identify via routine laboratory methods
- Intrinsic resistance to many antibiotics
- Require complex and prolonged duration of antimicrobial therapy
- Ability to infect a wide range of animals as well as humans
- Persistence in the environment (weeks for B mallei and years for B pseudomallei)
- No currently available vaccines
Several countries have studied glanders as a bioweapon, and it may have been the first biological weapon used in the 20th century.
- During World War I, Germany used biological sabotage against several countries, including the United States, Argentina, Norway, Romania, Russia, and Spain (Martin 2007, Wheelis 1998). Apparently, German espionage units brought Bacillus anthracis and B mallei cultures to the United States from Germany in 1915 and 1916 and established a secret laboratory in Maryland. These cultures were used to infect animals destined for shipment to Allied countries in Europe (Kasten 2002). Infected animals were shipped with the dual purpose of infecting livestock and transmitting the agent from livestock to humans (Wheelis 1998). The Germans also used B mallei to infect large numbers of horses and mules on the Eastern Front in Russia, an action that affected troop movements by restricting the supply of draft animals (Bossi 2004).
- During World War II, the Japanese deliberately infected animals and humans with B mallei, including prisoners of war, at the Ping Fan Institute in China (Bossi 2004, Croddy 2002, Harris 1999).
- The United States studied B mallei as a possible biowarfare agent in the early 1940s but did not weaponize it (Rega 2009).
- The Soviets conducted experiments to modify B mallei to enhance antibiotic resistance (Waag 2005), and the organism was reportedly used by Soviet troops against the mujahedeen in Afghanistan between 1982 and 1984 (Alibek 1999, Waag 2005).
- A report on the potential for biological agents to be used against food and water supplies concluded that B mallei has limited potential to contaminate a water supply and is not considered to be a foodborne pathogen (Khan 2001).
The United States signed the Convention on the Prohibition of the Development, Production and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on Their Destruction in 1972. Offensive biological warfare work at Fort Detrick, Maryland, had ceased prior to that time, and any remaining biological weapons were destroyed by 1973. Ongoing research is aimed at the biodefense of B mallei, B pseudomallei, and other agents. Although there are no known current attempts for acquisition or use of these organisms by terrorists, a determined bioterrorist most likely could obtain the agent from the environment (B pseudomallei), an infected animal, laboratory culture, or commercial culture (Gregory 2007).
For some bioterrorism agents, animals may serve as sentinels for an aerosol bioterrorism attack. One report assessed this potential for a number of possible bioterrorism agents and determined that there was insufficient evidence that animals (eg, horses) would be useful sentinels for an attack caused by B mallei (Rabinowitz 2006). Horses could, however, serve as markers for ongoing exposure risk or could serve as a reservoir for maintaining the organisms in the environment following an attack.
Diverse bacteria, including select agents, have been detected in urban air by DNA arrays. Pathogenic bacteria, including B mallei and B pseudomallei, were found in Austin and San Antonio, Texas, during a 17-week study of airborne bacterial composition and dynamics (Brodie 2007).
The clinical course of glanders described below is based on reports of cases published before antibiotics were available and a reported series of laboratory-acquired cases in the United States (Gregory 2007). Human glanders can be acute or chronic, with the mode of infection, inoculating dose, intrinsic virulence, and host risk factors determining the clinical course.
Most sources indicate that the infectious dose is probably relatively low for B mallei, although it has not been well quantified. Japan's biological warfare group, Unit 731, estimated the infectious dose (ID50) of B mallei to be 0.2 mg by subcutaneous inoculation, but the equivalent dose in colony-forming units (CFUs) is not clear (Harris 1999).
Glanders has a varied clinical picture, and illness generally can be characterized into one of four clinical syndromes: localized, pulmonary, septicemic, or chronic. None of these forms is exclusive (CDC 2012: Glanders, Gregory 2007, Rega 2009, USAMRIID 2011).
The clinical features of glanders are summarized below.
Clinical Features of Glandersa
—Localized infection: 1-5 days
Because human infections are rare, the incubation period has not been well defined, particularly for inhalational exposures.
The course of illness is variable; disease may remain active for months or years, and relapses can occur.
Latent periods between relapses can last for up to 10 years.
Signs and symptoms: localized form
Localized cutaneous infection:
Localized mucous membrane infection:
—Erosion of the nasal septum and turbinates may occur if infection involves the nares.
Signs and symptoms: pulmonary form
—Pneumonia, pulmonary abscess, and pleural effusion can occur.
Pulmonary disease may arise from direct inhalation or via hematogenous spread.
Signs and symptoms: septicemic form
—May occur at any point in the illness.
—Granulomatous or necrotizing lesions may occur in any organ.
Signs and symptoms: chronic form
—Multiple abscesses may occur in muscle tissue of the arms and legs or in the lungs, liver, or spleen.
—Abscesses should undergo surgical drainage.
—Slight leukocytosis or leukopenia may be present.
Diagnosis is confirmed by isolating the organism from blood, sputum, abscess material, or tissue.
—The septicemic form is generally fatal within 7-10 days if untreated.
Because the disease is rare, it is not clear what the mortality rates are with currently available antibiotic regimens.
aBartlett 2004, USAMRIID 2011.
The clinical manifestations of melioidosis are extremely diverse, and as such, it is sometimes called "the great imitator." Additionally, the unusually broad range of presentations has resulted in a variety of classifications, one of which is similar to that used for glanders; it includes the following forms: localized, pulmonary, septicemic, and disseminated. The disease may progress from one form to another over time (CDC 2012: Melioidosis, Rega 2009, USAMRIID 2011, Vietri 2007).
The clinical features of melioidosis are outlined in the following table.
Clinical Features of Melioidosisa
In those with acute disease, the incubation period generally ranges from 1-21 days, with an average of 9 days.
The incubation period has not been well defined for nonacute cases, since the inoculating event may go unrecognized and a long latent period may occur.
The course of illness is variable; disease may be acute and fulminant or may remain indolent for months or years.
Remitting/relapsing disease can occur.
Signs and symptoms: localized form
—The localized form usually results in a cutaneous nodule, ulcer, or skin abscess at the site of inoculation.
Surgical drainage of large abscesses is indicated.
Signs and symptoms: pulmonary form
—Pulmonary involvement can range from a relatively mild undifferentiated illness to fulminant pneumonia with septic shock.
—Pulmonary involvement is the most common manifestation of disease and occurs in approximately half of cases.
Signs and symptoms: septicemic form
—Signs and symptoms are consistent with a typical sepsis syndrome.
This form occurs most commonly in persons with underlying conditions, notably diabetes, renal disease, alcoholism, and chronic lung disease.
Signs and symptoms: disseminated form
—Multiple abscesses can occur throughout the body; liver, spleen, skeletal muscle, kidneys, and prostate are the most common sites.
Surgical drainage of large abscesses is indicated.
—Gram's stain of sputum and abscess material may reveal gram-negative bacilli. The organisms often have a characteristic bipolar staining with a "safety pin" appearance.
Diagnosis is confirmed by isolating the organism from blood, sputum, abscess material, or tissue.
Complications are primarily related to abscess formation and suppuration. Examples include brain stem encephalitis with limb weakness and cranial nerve palsies, osteomyelitis, and septic arthritis.
—The case-fatality rate for septicemic disease is about 90% without treatment and 40% to 75% with treatment.
A prospective study in Thailand identified 230 adult culture-confirmed melioidosis patients in which 77 (33%) had an abscess (Maude 2012). The spleen and liver are the most common sites of abscesses, with most patients having multiple abscesses. Seventy-three percent of patients with abscesses did not experience abdominal pain, and those with abscesses had a lower mortality rate after discharge.
As noted in the table above, neurologic complications, while rare, can occur with melioidosis. In some instances patients can present with neurologic signs or symptoms. In one case report, a patient with risk factors for melioidosis presented with pneumonia and appeared to have a stroke in the emergency department (Kung 2013). Despite antibiotic therapy, the patient died. In another case report, a young rice farmer in an endemic area presented with limb weakness and numbness (Nandasiri 2012). A CT scan showed a psoas abscess that resulted in transverse myelitis. B pseudomallei was isolated from the abscess, and the patient was successfully treated, but paralysis remained.
Melioidosis is rarely reported in neonates, with only 22 cases in the known literature (Thatrimontrichai 2012). The clinical presentations were non-specific, with most cases having bacteremia. The most common diagnosis was bacteremia with pneumonia (50% of cases). Maternal transmission (vertical and via breast milk) occurred in two cases. Healthcare or community transmission occurred in eight cases. The mortality rate for neonate melioidosis was 73%, with 16 neonates dying. No clear guidelines are available for treating neonates who have melioidosis.
Images of B mallei and B pseudomallei colony morphology can be viewed on the CDC's Web site (CDC: Public Health Image Library). Radiologic images of melioidosis and how they differ from tuberculosis and staphylococcal pneumonia are provided in a review by Burivong et al.
Many of the features of glanders and melioidosis are nonspecific; therefore, multiple different infections may be included in the differential diagnosis.
The clinical presentations for melioidosis, which is caused by the related pathogen, B pseudomallei, can be similar to those for glanders. Thus, only the differential diagnoses for glanders clinical syndromes are presented here.
Bubonic plague (Yersinia pestis)
—Clinical course often fulminant
Cat-scratch disease (Bartonella henselae)
—History of contact with cats; usually history of cat scratch
Mycobacterial infection, including scrofula (Mycobacterium tuberculosis, M marinum)
—With scrofula, adenitis occurs in cervical region
Sporotrichosis (Sporothrix schenckii)
—Lymph nodes generally painless and nontender
Streptococcal or staphylococcal lymphangitis (Staphylococcus aureus, Streptococcus pyogenes)
—Site of initiating infection often present distal to involved nodes (ie, pustule, infected traumatic lesion)
Ulceroglandular or oculoglandular tularemia
—Tularemia may affect skin or eyes, similar to glanders
Community-acquired bacterial pneumonia
—Legionellosis and many other bacterial agents (S aureus, S pneumoniae, H influenzae, K pneumoniae, M catarrhalis) usually occur in persons with underlying pulmonary or other disease or in elderly
Inhalational anthrax (Bacillus anthracis)
—Widened mediastinum and pleural effusions seen on CXR or chest CT
Pneumonic plague (Y pestis)
—Hemoptysis commonly occurs
Pneumonic tularemia (F tularensis)
—Illness may be rapidly progressive and severe or may be indolent with progressive weakness and weight loss over several weeks to months
Q fever (Coxiella burnetii)
—Exposure to infected parturient cats, cattle, sheep, goats
Tuberculosis (M tuberculosis)
—More common among elderly or among persons who have lived in tuberculosis-endemic countries (eg, developing world, countries of the former Soviet Union)
—Influenza generally seasonal (October-March in United States) or involves history of recent cruise ship travel or travel to tropics
Brucellosis (Brucella melitensis, B abortus, B suis)
—Usually history of contact with tissues, blood, aborted fetuses of infected animals (cattle, swine, goats, sheep)
Endocarditis (varied causes)
—Features of endocarditis (eg, cardiac murmur, embolic phenomenon) often present
Leptospirosis (Leptospira interrogans)
—History of exposure to infected animals or to water or soil contaminated with urine from infected animals
Malaria (Plasmodium species)
—History of travel to malaria-endemic area usually present
Meningococcemia (Neisseria meningitidis)
—Rapid progression to shock and often death
Q fever (C burnetii)
—Exposure to infected parturient cats, cattle, sheep, goats
Septicemic plague (Y pestis)
—Often secondary to bubonic plague (characteristic bubo present in groin, axilla, or cervical region)
Septicemia caused by other gram-negative bacteria
—Underlying illness usually present
Smallpox (variola major virus)a
—The rash associated with septic glanders may be similar to the pustular lesions seen with smallpox
Staphylococcal or streptococcal TSS (S aureus, S pyogenes)
—Streptococcal TSS may be associated with necrotizing fasciitis
Typhoid fever (Salmonella typhi)
—Symptoms of enterocolitis and abdominal pain may be more prominent with typhoid fever
Typhoidal tularemia with sepsis (F tularensis)
—Category A bioterrorism agent
Syphilis (Treponema pallidum)a
—A range of symptoms may be present
Tuberculosis (M tuberculosis)a
—Pulmonary involvement usually present
B mallei and B pseudomallei have been reported to cause laboratory-acquired infections due to manipulation of cultures of these organisms using biosafety level 2 (BSL-2) practices. Infections were due to either inhalation of infectious aerosols or direct skin exposure (CDC 2009).
Experience has shown that B mallei can be very hazardous in the laboratory setting. For example, in the pre-biosafety era, nearly one half of laboratory workers in a B mallei research laboratory became infected within 1 year of working with the organism (CDC 2009).
- During World War II, six unrelated cases occurred in laboratory workers at Camp Detrick in Frederick, Maryland; some cases were inhalational and for some the source of infection was not identified (CDC 2009, Gregory 2007).
- Another previously unpublished case also occurred in a Camp Detrick employee in 1953; the likely route of exposure was inhalation (Gregory 2007).
- In 2000, a case occurred in a microbiologist who worked at the US Army Medical Research Institute for Infectious Diseases (USAMRIID) in Maryland. No clear exposure was identified, although he occasionally handled without gloves equipment containing live Burkholderia strains (CDC 2000, Gregory 2007, Srinivasan 2001). The patient was treated with antibiotics and recovered; he had type 1 diabetes.
- Worldwide, more than 25 laboratory-acquired glanders infections have been reported (Galyov 2010).
Two cases of laboratory-acquired melioidosis have been documented.
- A 1968 report described a case of melioidosis in a Canadian laboratory worker who had cleaned a centrifuge spill of B pseudomallei organisms without wearing gloves. At the time of the incident, the worker had an ulcerative lesion at the base of one finger. Thus, it is unclear whether the infection resulted from inhalation or percutaneous inoculation. The patient recovered after treatment with several antibiotics (Green 1968).
- In 1980, a US laboratory technician developed melioidosis after working with a clinical isolate from a Vietnam veteran. The isolate initially was identified as B cepacia but was later determined to be B pseudomallei. The technician routinely performed open-flask sonication of a suspension of organisms outside of a biological safety cabinet (BSC), presumably resulting in inhalational exposure (Schlech 1981). After a prolonged course of antimicrobial therapy, the patient fully recovered.
Recognized laboratory hazards include the following (CDC 2009):
- Exposure to infectious aerosols or droplets through manipulation of cultures
- Direct contact of skin or mucous membranes with infectious materials
- Accidental parenteral inoculation
- Accidental ingestion
To prevent such exposures, the Centers for Disease Control and Prevention (CDC) recommends the following laboratory practices for B mallei and B pseudomallei (CDC 2009).
- BSL-2 practices, containment equipment, and facilities in a BSC are recommended for primary isolations from patient fluids or tissues.
- Biosafety level 3 (BSL-3) practices, containment equipment, and facilities are recommended whenever infectious aerosols or droplets are generated, such as during centrifugation or handling infected animals, or when large quantities of the agent are produced. Antimicrobial susceptibility testing should be performed only under BSL-3 conditions.
- Procedures conducted outside of a BSC that generate infectious aerosols require respiratory protection.
- Sealed cups should be used with all centrifuges, and these should be opened only inside a BSC.
- Gloves should be worn when working with potentially infectious materials or animals. Animal work with B mallei and B pseudomallei should be done with animal BSL-3 practices, containment equipment, and facilities.
Both B mallei and B pseudomallei are classified as select agents and therefore are regulated under 42 CFR part 73 (Possession, Use, and Transfer of Select Agents and Toxins), which was published in final form in the Federal Register in March 2005 (HHS 2005).
- As specified in the Public Health Security and Bioterrorism Preparedness and Response Act of 2002, 42 CFR part 73 provides requirements for laboratories that handle select agents (including registration, security risk assessments, biosafety plans, security plans, incident response plans, training, transfers, record keeping, inspections, and notifications).
- Select agents are biological agents designated by the US government to be major threats to public health and safety. A current list of select agents is published on the National Select Agent Registry Web site (CDC/APHIS 2008).
- As specified in the Select Agent Rule, agents must be shipped according to applicable regulations. These regulations are outlined in the CDC guidance, Biosafety in Microbiological and Biomedical Laboratories, under Appendix C: Transportation of Infectious Substances (CDC 2009) and the International Air Transport Association’s Infectious Substances Shipping Guidelines (IATA 2009). The American Society for Microbiology (ASM) also has guidelines for packing and shipping infectious substances that outline current requirements (ASM 2010).
In 2002, the CDC published additional guidelines for enhancing laboratory security for laboratories working with select agents (CDC 2002). These guidelines should be followed to promote laboratory security and prevent the potential misuse of select agents.
The LRN is a network of more than 150 national and international laboratories. The network includes federal, state and local public health, military, food testing, environmental, and veterinary laboratories. The international laboratories are located in Canada, the United Kingdom, Australia, Germany, South Korea, and Japan (CDC: Facts about the Laboratory Response Network; CDC: Laboratory Response Network).
The LRN structure for bioterrorism designates laboratories as sentinel, reference, or national. Designation depends on the types of tests a laboratory can perform and how it handles infectious agents to protect workers and the public.
- Sentinel laboratories, formerly called level A laboratories, represent an estimated 25,000 hospital-based labs that are on the front lines. Sentinel laboratories have direct contact with patients. In an unannounced or covert terrorist attack, patients provide specimens during routine patient care. Sentinel laboratories could be the first facilities to encounter a suspicious specimen. A sentinel laboratory’s responsibility is to rule out B mallei or B pseudomallei or refer a suspicious sample to the nearest LRN reference laboratory. These laboratories generally have at least BSL-2 containment. Sentinel laboratories use the ASM Sentinel Level Clinical Microbiology Laboratory Guidelines to rule out microorganisms that might be suspected as agents of bioterrorism (ASM: Sentinel level clinical microbiology laboratory guidelines).
- Reference laboratories, sometimes referred to as "confirmatory reference" and formerly called level B or C laboratories, can perform tests to detect and confirm the presence of a threat agent. These laboratories ensure a timely local response in the event of a terrorist incident. Rather than having to rely on confirmation from laboratories at the CDC, reference laboratories are capable of producing conclusive results; this allows local authorities to respond quickly to emergencies. These are mostly state or local public health laboratories but also include military, international, veterinary, agriculture, food, and water testing laboratories. Reference laboratories operate with BSL-3 containment facilities and have been given access to nonpublic testing protocols and reagents. One of the roles of the LRN reference laboratories is to provide guidance, training, outreach, and communications to the sentinel laboratories in their jurisdiction. State public health laboratories can provide information about the nearest LRN reference laboratory (APHL 2013).
- National laboratories, formerly called level D laboratories, have unique resources to handle highly infectious agents and the ability to identify specific agent strains through molecular characterization methods. National laboratories, which include laboratories at the CDC and USAMRIID, have the highest level of containment (BSL-4). These laboratories also are responsible for methods development, bioforensics, and select agent activity.
When the diagnosis of glanders or melioidosis is being considered, the hospital clinical laboratory should be alerted, because some laboratories will not further identify Burkholderia species unless specifically requested. The ASM, in collaboration with the CDC and the Association of Public Health Laboratories (APHL), has developed sentinel laboratory guidelines to enable clinical laboratories to perform microbiological analyses to rule out B mallei and B pseudomallei (ASM 2013).
When glanders or melioidosis is suspected or B mallei or B pseudomallei cannot be ruled out, sentinel laboratories should contact their LRN reference laboratory for specimen collection consultation and isolates should be referred for confirmation testing.
Glanders and melioidosis are definitively diagnosed by isolation and identification of B mallei and B pseudomallei, respectively. The most common types of specimens collected from suspected cases include blood, sputum, bone marrow, tissue, abscess/wound material, and urine. Blood cultures often are negative unless the disease stage is advanced (ASM 2006, ASM 2013, Gregory 2007).
- Blood cultures: Collect two sets per institutional protocol for routine blood culture or collect lysis-centrifugation (eg, Isolator) blood cultures. Transport at room temperature. Incubate at 35ºC to 37ºC, ambient atmosphere; CO2 incubation is acceptable.
- Bone marrow: Collect per institutional protocol. Transport within 2 hours at room temperature. If storage is required, store at 4ºC for <24 hours. Incubate at 35ºC to 37ºC, ambient atmosphere; CO2 incubation is acceptable.
- Respiratory specimens, abscess/wound material, urine: Collect per institutional protocol. Transport within 2 hours at room temperature. If storage is required, store at 4ºC for <24 hours. Incubate at 35ºC to 37ºC, ambient atmosphere; CO2 incubation is acceptable.
The information below is taken from the available ASM guidelines for isolation and identification of B mallei and B pseudomallei (ASM 2013). When B mallei and B pseudomallei cannot be ruled out, sentinel laboratories should contact their LRN reference laboratory, and isolates should be referred for confirmation testing.
Inoculation and Plating Procedures
The following media should be used for isolation:
- Blood cultures: Should be processed according to standard laboratory procedures.
- Respiratory specimens, abscess/wound material, urine: Should be plated directly onto sheep blood agar (SBA), chocolate agar, and MacConkey agar; enrichment broth can be used for wound/abscess material.
The following procedures should be used for isolation:
- Primary plates should be held for a minimum of 5 days and read daily, although B mallei may grow slowly and may require an extended incubation time.
- Plates should be taped shut when incubating. Both B mallei and B pseudomallei laboratory-acquired infections have been reported. Thus, sniffing plates should never be practiced (ASM 2013; CDC 2004: Laboratory exposure to Burkholderia pseudomallei).
- Selective media may be used to aid isolation of B mallei and B pseudomallei from specimens collected from nonsterile sites with an extensive normal flora. Ashdown's selective-differential agar medium was specifically designed for the recovery of B pseudomallei (Ashdown 1979, Francis 2006). However, as these media are not routinely available in sentinel laboratories, B cepacia selective agar medium can be used for the isolation of B pseudomallei (ASM 2013, Peacock 2005). B cepacia selective medium contains aminoglycosides and therefore has limited use for the isolation of B mallei, as this organism typically is susceptible to these antimicrobial agents. An older formulation of this selective medium called PC agar (from the former name of the organism, Pseudomonas cepacia) may be used to isolate B mallei, as this medium uses ticarcillin rather than aminoglycosides as a selective agent.
- When PC agar or B cepacia selective media are not available, a polymyxin B disk or colistin (polymyxin E) disk may be placed in the initial inoculation area of the SBA for specimens collected from nonsterile sites. B mallei and B pseudomallei are resistant to these agents and will therefore grow up to the disk, whereas many commensal organisms will be inhibited. Thus, if present in the specimen, B mallei or B pseudomallei could be recovered from the area adjacent to the disk (ASM 2013).
- In exudates and purulent material, B mallei organisms are often few and often morphologically indistinguishable from B pseudomallei, but they can be cultured and identified with standard bacteriologic media; adding 1% to 5% glucose, 5% glycerol, or meat infusion nutrient agar may accelerate growth (USAMRIID 2011).
- Isolation of B pseudomallei from specimens containing normal flora may be accomplished by growth at 42ºC, in 2% sodium chloride solution, or on MacConkey agar. B mallei will not grow under these conditions (Gregory 2007).
- Various manual and automated culture identification systems have been reviewed (O'Hara 2005). Automated culture identification systems usually are more rapid than manual culture methods but present a biosafety risk, because a high concentration of organism in liquid suspension is required for these systems. In addition, since many automated systems are ideally suited to the identification of rapidly growing organisms, misidentifications have been observed with slow-growing B mallei and B pseudomallei. Automated systems also are limited because their databases often include only a small number of strains (Lowe 2002, Weissert 2009). Some manual systems, such as the API 20NE and RapID NF Plus, can be used for preliminary testing to identify B pseudomallei and B mallei strains, but they are not reliable for confirmatory identification (Glass 2005).
- B mallei and B pseudomallei may be misidentified as a Pseudomonas species, and gene sequence analysis or organism-specific polymerase chain reaction (PCR) assays may be required for confirmation (Currie 2010).
Appearance and Biochemical Properties
Appearance and biochemical properties for B mallei and B pseudomallei are outlined in the table below (ASM 2013, Gilligan 2003).
Appearance and Biochemical Properties of Burkholderia mallei and B pseudomallei
Aerobic (facultatively anaerobic in the presence of nitrate)
Aerobic (facultatively anaerobic)
—Coccobacillus (or small rod with round ends)
—Bacillus (small straight or slightly curved rod)
+ or –
+ (without gas)
+ (with gas)
Resistance to colistin or polymyxin B
Appearance on SBA
—Poor growth at 24 hr; better growth at 48 hr
—Poor growth at 24 hr; good growth at 48 hr
Growth on MacConkey agar
Grows well on this medium
TSI or KIA agar
—TSI or KIA butt: red (no change)
—TSI or KIA butt: red (no change)
No distinctive odor
Produces strong, distinctive musty or earthy odor
Agglutination tests and complement fixation (CF) assays have been developed (mainly for use in animals); currently no serologic test for diagnosing B mallei in humans is available in the United States (ASM 2013, Bartlett 2004, Currie 2010).
Agglutination assays are not positive for at least 7 to 10 days (sometimes up to 3 weeks) after infection (USAMRIID 2011).
CF tests are more specific than the agglutination test, but less sensitive and may take up to 40 days for conversion. CF tests are considered positive if the titer equals or exceeds 1:20 (USAMRIID 2011).
Some serologic assays cannot distinguish B mallei from B pseudomallei since antibodies recovered from patients with culture-confirmed melioidosis have been found to cross-react with B mallei (Tiyawisutsri 2005).
Serologic assays developed for B pseudomallei include indirect hemagglutination assay, dot immunoassay, and enzyme-linked immunosorbent assay (Cheng 2006, Sermswan 2000). Melioidosis cannot be reliably diagnosed by serologic testing alone because of the high antibody prevalence to B pseudomallei among healthy individuals in endemic regions (Vietri 2007).
In recent years, the difficulties in identifying these pathogens have led to the development and application of molecular methods. Such methods may be used for directly detecting (or ruling out) the presence of B mallei or B pseudomallei in clinical specimens, or for the final identification of isolates recovered from clinical specimens. Additionally, several approaches have been developed specifically to distinguish between B mallei and B pseudomallei isolates. At this time, these methods generally are available only in reference or research laboratories. They include PCR assays, PCR-derived restriction length polymorphism, gene sequencing, pulsed-field gel electrophoresis (PFGE), variable number tandem repeat polymorphism, and multilocus sequence typing (CFSPH 2007: Glanders, CFSPH 2007: Melioidosis, Gilad 2007, Kaestli 2012, Price 2012).
Key points regarding treatment of glanders and melioidosis are as follows:
- Given the rarity of recent human glanders cases, definitive information about antibiotic treatment is scarce; however, the antibiotic susceptibility patterns for B mallei and B pseudomallei are similar, and experience gained in treating melioidosis, which is much more common, may be applicable to glanders (USAMRIID 2011).
- B mallei is usually sensitive to tetracyclines, ciprofloxacin, streptomycin, novobiocin, gentamicin, imipenem, ceftazidime, and sulfonamides (CDC 2012: Glanders, HPA 2008, USAMRIID 2011).
- Sulfadiazine is effective in animal models and in human cases. Six glanders cases in laboratory workers during World War II were treated with sulfadiazine (Gregory 2007, Howe 1947).
- In a laboratory-acquired case of glanders in 2000, an infected worker was treated initially with a 10-day course of clarithromycin, but he had a relapse 4 days later. He was then treated with a regimen of imipenem and doxycycline; after 2 weeks, the imipenem was switched to azithromycin and he completed a 6-month course of azithromycin and doxycycline (Srinivasan 2001).
- Tetracycline and streptomycin can be used in combination to treat glanders, with streptomycin and chloramphenicol constituting an alternative regimen (Rosenbloom 2002).
- The US Food and Drug Administration (FDA) has yet to specifically approve the use of any antimicrobials for treatment or postexposure prophylaxis of B mallei infections. Any antibiotics used for treatment would require emergency use authorization by the FDA or off-label use (Larsen 2009). Few antibiotics have been evaluated in vivo, because the disease had largely disappeared by the time antibiotics became available.
- B pseudomallei usually is sensitive to ceftazidime, imipenem, meropenem, doxycycline, trimethoprim-sulfamethoxazole, piperacillin, amoxicillin-clavulanic acid, azlocillin, ticaricillin-clavulanate, ceftriaxone, and aztreonam (CDC 2012: Melioidosis).
US Public Health Service Treatment Recommendations
The US Public Health Emergency Medical Countermeasures Enterprise convened subject matter experts in 2010 to develop consensus recommendations for treatment for and postexposure prophylaxis against B pseudomallei and B mallei infections during a mass exposure incident; these guidelines were published in November 2012 (Lipsitz 2012). The recommendations are directed primarily toward treatment for melioidosis; however, participants agreed that recommendations would be similar for glanders.
Treatment recommendations are divided into two phases: intensive-phase treatment and eradication-phase treatment. During the intensive phase of treatment, patients should receive parenteral therapy, and once they enter the eradication phase, they can be treated orally. Current treatment recommendations are outlined in the two tables below.
Intensive-Phase Treatment of Glanders and Melioidosis During a Public Health Emergencya
Regimen for Suspected or Confirmed Clinical Cases (10-14 day duration)a
50 mg/kg (up to 2 g IV) every 8 hr
With neuromelioidosis, bacteremia, or in the ICU
25 mg/kg (up to 1 g) IV every 8 hr
Eradication-Phase of Glanders and Melioidosis
Regimen for Suspected or Confirmed Clinical Cases (min 12-wk duration)
Amoxicillin/clavulanic acid (co-amoxiclav)b
Amoxicillin/clavulanic acid (co-amoxiclav):
Abbreviations: TMP/SMX, trimethoprim/sulfamethoxazole.
aIf susceptible and patient can tolerate.
Adapted from Lipsitz 2012.
BICHAT Treatment Recommendations
The European Commission's Task Force on Biological and Chemical Agent Threats (BICHAT) has published guidelines for treatment of glanders and melioidosis, but all treatment recommendations should be adapted according to the susceptibility reports from any isolates obtained (Bossi 2004). The BICHAT guidelines are outlined in the table below.
Treatment of Glanders and Melioidosis
Regimen for Suspected or Confirmed Clinical Cases (2-3 wk duration)a
Adults, pregnant womenb
Combination treatment with imipenem or meropenem or ceftazidime in severe cases
Combination treatment with imipenem or meropenem or ceftazidime in severe cases
Postexposure treatment with doxycycline provided complete protection from lethal inhalation challenge of B pseudomallei in mice treated with the equivalent of a standard human dose of doxycycline 6 hours postexposure (Gelhaus 2013).
Because of the difficulty in treating the organisms and the potential for relapse, some guidelines recommend follow-up for at least 5 years postrecovery and perhaps even lifelong (HPA 2008, USAMRIID 2011).
In addition to clinical and radiographic monitoring of resolution of focal infection, inflammatory markers such as C-reactive protein may provide an early indication of relapse. Consideration should be given to repeating cultures regularly (ie, weekly during parenteral treatment and monthly afterward) during convalescence to detect emergence of resistance to the antibiotics used (HPA 2008). Veno-venous extracorporeal membrane oxygenation (ECMO) may be used as supportive care in patients with refractory hypoxemia and severe septic shock (van der Geest 2013).
Antimicrobial Susceptibility Studies
Antibiotics proven clinically effective in treating melioidosis are likely to be effective in treating glanders, based on the relatedness between the two organisms (Kenny 1999, Rusnak 2004); however, B pseudomallei has a unique drug efflux system that is specific for both aminoglycosides and macrolides (Thibault 2004), which creates intrinsic resistance to these agents.
A review of data from 4,021 patients with melioidosis identified 24 patients with one or more isolates resistant to ceftazidime, and/or amoxicillin-clavulanic acid, suggesting that resistance to these first-line drugs is rare (Wuthiekanun 2011). In another study, six clinical isolates resistant to ceftazidime that failed to grow on commonly used laboratory media were analyzed; all had significant genomic loss, which included the gene encoding penicillin-binding-protein 3 (Chantratita 2011). In a third study, B pseudomallei isolates from four patients with recurring melioidosis had genetic changes that were associated with antibiotic resistance, suggesting that resistance plays a significant role in these infections (Hayden 2012).
Investigators tested susceptibilities of 50 isolates of B pseudomallei and 15 isolates of B mallei against 35 antimicrobial agents, including newer and previously untested drugs (Thibault 2004). Results showed that B mallei strains tested were highly resistant (70% to 100%) to:
MICs of Various Antibiotics for B pseumallei and B malleiIsolates
B pseudomallei (50 strains)
B mallei(15 strains)
No human vaccines are currently available for preventing glanders or melioidosis, but research with animal models and candidate vaccines is ongoing. Furthermore, no definitive evidence exists that infection with B pseudomallei confers long-term immunity, because reinfection with a different strain has occurred after successful treatment (Vietri 2007). Of the several vaccines for B pseudomallei in development, none has been tested in diabetes models, which is crucial given that diabetes is a significant risk factor for melioidosis (Peacock 2012).
Consensus recommendations for responding to a public health emergency involving B mallei or B pseudomallei have been developed in the United States (Lipsitz 2012). Treatment recommendations are outlined in the Treatment & Vaccines section, and recommendations for postexposure prophylaxis are outlined in the table below.
Postexposure Prophylaxis for Glanders and Melioidosis
Regimen for Suspected or Confirmed Clinical Cases (21-day duration)
Amoxicillin/clavulanic acid (co-amoxiclav)b:
Amoxicillin/clavulanic acid (co-amoxiclav):
Additional information on postexposure prophylaxis is also available.
- Trimethoprim-sulfamethoxazole (TMP-SMX) and quinolones (administered for 10 days) have been shown to be effective in white rats for B pseudomallei postexposure prophylaxis (Batmanov 2004).
- In a case of laboratory exposure to B pseudomallei, 16 workers completed a 3-week regimen of TMP-SMX, and 1 completed a 3-week regimen of doxycycline. Treatment regimens were started from 2 to 4 days after exposure. Thirteen of the workers reported high-risk activities in the laboratory setting, including 4 who reported sniffing a culture plate of B pseudomallei because of its distinctive earthy odor. None of the exposed workers had symptoms consistent with melioidosis during a 5-month follow-up (CDC 2004: Laboratory exposure).
- BICHAT has proposed the use of TMP-SMX for use as prophylaxis after a biological attack (Bossi 2004).
- In the United Kingdom, regimens of doxycycline (100 mg orally twice daily) or co-trimoxazole (960 mg orally twice daily) have been recommended following exposure. For children younger than age 12, a regimen of sulfamethoxazole (40 mg/kg) and trimethoprim (8 mg/kg) orally per day has been suggested (HPA 2008).
Guidance has been developed about the management of accidental laboratory exposures on the basis of experience with B pseudomallei. The recommendations for management of B mallei exposure are the same as for B pseudomallei, except for one important difference. No validated serologic test exists for human glanders; thus, recommendations based on antibody status or seroconversion do not apply, although serum should be taken and stored. Experts have proposed that the following actions be taken before and after an exposure incident (Peacock 2008):
- Baseline serum samples should be obtained from all newly employed workers and stored at –80ºC.
- Written protocols should be developed describing how to manage accidental exposures, including decontamination procedures, risk assessment, medical follow-up, long-term monitoring, sources of expert advice, and required notification and recordkeeping.
- If an exposure occurs, the site of contamination or inoculation should be immediately and thoroughly washed with water, followed by use of an appropriate cutaneous disinfectant.
- Following decontamination, an exposed worker must immediately seek medical attention, and the organism, type of exposure, and other pertinent information should be disclosed.
- Every exposure incident must be treated as potentially significant, and a risk assessment should be conducted. High-risk incidents include contact with B pseudomallei or B mallei via:
- Needlestick or other penetrating injury with a contaminated implement
- Bite or scratch by an infected experimental animal
- Splash event involving the eyes or mouth
- Generation of aerosol outside a BSC
- The exposed worker involved in a high-risk incident should begin postexposure prophylaxis and be monitored for evidence of adverse drug effects and evidence of clinical disease. Although there is no evidence for efficacy of postexposure prophylaxis in humans, TMP-SMX, doxycycline, and other antibiotics have been recommended.
- The exposed worker should be instructed to take and record his or her temperature twice daily for 21 days after the incident, and medical attention should be sought promptly if body temperature exceeds 38ºC or if a cough develops.
- Serum samples should be taken on the day of the exposure event and at 1, 2, 4, and 6 weeks; store samples at –80ºC.
- If the exposed worker develops febrile illness, cough, or inflammation at a known inoculation site, blood cultures (initially two sets from different venipuncture sites), sputum culture, throat swab, urine culture, and a chest radiograph should performed.
- The exposed worker with culture-confirmed infection should be treated with an intensive phase of intravenous antibiotics, followed by an eradication phase of oral antibiotics (Bossi 2004, HPA 2008, Peacock 2008).
- Clinical judgment will determine duration of postexposure prophylaxis, treatment, and follow-up.
In a situation of laboratory exposure to B pseudomallei, 16 workers completed a 3-week regimen of TMP-SMX, and 1 completed a 3-week regimen of doxycycline. Treatment regimens were started from 2 to 4 days after exposure. Thirteen of the workers reported high-risk activities in the laboratory setting, including 4 who reported sniffing a culture plate of B pseudomallei because of its distinctive earthy odor. None of the exposed workers had symptoms consistent with melioidosis during a 5-month follow-up (CDC 2004: Laboratory exposure).
Standard Precautions should be implemented for hospitalized patients; these include the following practices related to direct patient care (CDC/HICPAC):
- Hand washing:
- Wash hands after touching blood, secretions, excretions, other body fluids, or contaminated items, whether or not gloves are worn.
- Wash hands immediately after gloves are removed, between patient contacts, and when otherwise indicated to avoid transfer of microorganisms to other patients or environments.
- Wear gloves when touching blood, secretions, excretions, other body fluids, or contaminated items; put on clean gloves just before touching mucous membranes or nonintact skin.
- Change gloves between tasks and procedures on the same patient after contact with material that may contain a high concentration of microorganisms.
- Remove gloves promptly after use, before touching noncontaminated items or environmental surfaces, and before going to another patient, and wash hands immediately to avoid transfer of microorganisms to other patients or environments.
- Masks, eye protection, face shields:
- Wear a mask (ie, standard surgical mask) and eye protection or a face shield to protect mucous membranes of the eyes, nose, and mouth during procedures and patient-care activities that are likely to generate splashes or sprays of blood, secretions, or excretions, or other body fluids.
- Wear a gown to protect skin and prevent soiling of clothing during procedures and patient-care activities that are likely to generate splashes or sprays of blood, secretions, excretions, or other body fluids.
- Select a gown that is appropriate for the activity and amount of fluid likely to be encountered.
- Remove a soiled gown as promptly as possible and wash hands.
- Patient-care equipment:
- Handle used equipment soiled with blood, secretions, excretions, or other body fluids in a manner that prevents skin and mucous membrane exposures, contamination of clothing, and transfer of microorganisms to other patients or environments.
- Ensure that reusable equipment is not used for the care of another patient until it has been appropriately cleaned and reprocessed; single-use items should be appropriately discarded.
For patients who have a major draining abscess (or abscesses), Contact Precautions are recommended for the duration of illness. Contact Precautions include the following (CDC/HICPAC):
- Place the patient in a private room if available. If a private room is not available, place the patient in a room with a patient who has active infection with the same pathogen (ie, cohort). When a private room is not available and cohorting is not possible, a spatial separation of at least 3 ft should be maintained between the infected patient and other patients and visitors.
- Wear gloves when entering the room, change gloves after having contact with infectious material, remove gloves before leaving the room, and immediately wash hands using an antimicrobial agent.
- Wear a gown when entering the room if clothing will have significant patient contact; remove the gown before leaving the room.
- Move and transport the patient for essential purposes only. If transport is necessary, precautions should be maintained.
- When possible, dedicate the use of noncritical patient-care equipment. If equipment cannot be dedicated, then it should be adequately cleaned and disinfected between patients.
- Tularemia, viral hemorrhagic fevers, smallpox, Q fever, and glanders have been transmitted to personnel conducting autopsies, and some infections have been fatal (CDC 2004: Medical examiners, coroners, and biologic terrorism).
- Autopsy involves specific considerations because of the potential for aerosol generation and the intensity of potential exposures. To address these considerations, the CDC has issued a guidebook for autopsy and burial management for agents of bioterrorism (CDC 2004: Medical examiners, coroners, and biologic terrorism). Recommendations from the guidebook include the following.
- For autopsies, Standard Precautions include use of a surgical scrub suit, surgical cap, impervious gown or apron with full sleeve coverage, eye protection (eg, goggles or face shield), a mask or respirator, shoe covers, and double surgical gloves with an interposed layer of cut-proof synthetic mesh. BSCs should be available for handling and examination of smaller specimens; most are not designed to contain a whole body.
- Because of fine aerosols generated at autopsy, personnel should at a minimum wear a face-fitted N-95 respirator, regardless of suspected or known pathogen. Powered air-purifying respirators equipped with N-95 or HEPA filters should be considered.
- Protective outer garments should be removed when leaving the immediate autopsy area and discarded in appropriate laundry or waste receptacles, either in an antechamber to the autopsy suite or immediately inside the entrance if an antechamber is unavailable.
- Hand washing should be performed after glove removal.
- Standard safety practices include those to prevent injury from sharp items and to avoid contamination.
Standard Precautions should be followed while handling all cadavers before and after autopsy (CDC 2004: Medical examiners, coroners, and biologic terrorism).
The risks of occupational exposure to biological terrorism agents while embalming outweigh its advantages; therefore, bodies potentially infected with bioterrorism agents should not be embalmed. Cremation is the preferred method of disposal of the deceased (CDC 2004: Medical examiners, coroners, and biologic terrorism, HPA 2008). If cremation is not an option, the body should be properly secured in a sealed container (eg, Ziegler case or hermetically sealed casket) to reduce the potential risk of pathogen transmission.
Body fluids can be flushed or washed down ordinary sanitary drains; however, if substantial volumes are expected, local waste treatment personnel should be consulted in advance. Solid wastes should be appropriately disposed of in biohazard or sharps containers and burned in a medical waste incinerator (CDC 2004: Medical examiners, coroners, and biologic terrorism).
Glanders and melioidosis in humans are not listed as conditions to be reported to the US National Notifiable Disease Surveillance System maintained by the CDC. However, since these diseases do not occur naturally in the United States, suspect or confirmed cases should be reported to local or state public health authorities as soon as possible, according to disease-reporting rules within each state or local jurisdiction. A case of human glanders without history of animal exposure or more than one human case is presumptive evidence of bioterrorism (Gregory 2007).
Any presumptive isolates of B mallei or B pseudomallei also should be referred to an LRN reference laboratory (ASM 2013).
Glanders in animals is considered a foreign animal disease and should be reported immediately to the US Department of Agriculture through the appropriate state and local channels (APHIS).
No official case definition has been developed in the United States for glanders or melioidosis. The following case definition has been developed in the United Kingdom (HPA 2008):
- Suspect case:
- A patient with a severe febrile illness from whom an organism suspected of being B mallei or B pseudomallei has been isolated before the identity has been confirmed by the reference laboratory or
- A patient with severe febrile illness in whom antibodies to B mallei or B pseudomallei have been detected but from whom no isolate has been obtained or
- A patient with severe febrile illness who is known to have been exposed to B mallei or B pseudomallei
- Confirmed case: A case of severe febrile illness, with or without obvious foci of infection from whom reference laboratory-confirmed B mallei or B pseudomallei has been isolated
An evidence-based case definition for inhalational melioidosis includes the following criteria (Cheng 2013):
- Development of respiratory symptoms in the preceding 4 weeks
- Presence of sepsis, defined as two or more of:
- Body temperature < 36°C or > 38°C
- Heart rate > 90 beats per minute
- Respirations > 20 breaths per minute
- White cell count < 4 x 109 or > 12 x 109 cells/L or more than 10% band forms
- Evidence of alveolar infiltrate on chest x- ray within 48 hours of admission
- No evidence of percutaneous inoculation injury (in endemic areas or lab) and evidence for opportunity for inhalational exposure
- Isolation of B pseudomallei from any sterile or nonsterile body site
In addition, the CDC has recommended that healthcare providers be aware of the features of an intentional release of a biological agent so they can promptly report suspicious events before laboratory confirmation is obtained (CDC 2001). Examples of such features are:
- An unusual temporal or geographic clustering of illness (eg, persons who attended the same public event or gathering)
- Patients who have clinical signs and symptoms that suggest an infectious disease outbreak (eg, >2 patients presenting with an unexplained febrile illness associated with sepsis, pneumonia, respiratory failure, etc)
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