Melioidosis: Indian perspective
T Karuna1, Khadanga S2,
Dugar D3
1Dr T Karuna, Assistant Professor, Department of Microbiology,
AIIMS, Bhopal, Madhya Pradesh, India.2Dr Sagar Khadanga,
Associate Professor, Department of Medicine, L N Medical College,
Bhopal, Madhya Pradesh, India. 3Dr Dharmendra Dugar, Assistant
Professor, Department of Surgery, Hi tech Medical College, Bhubaneswar,
Odisha, India.
Address for
correspondence: Dr T Karuna, Email:
karunakhadanga@yahoo.co.in
Abstract
There has been an upsurge of melioidosis cases in India in recent past.
Lack of awareness of this disease among the Indian clinicians and
microbiologists is responsible for the wrong diagnosis as tuberculosis,
scrub typhus, leptospirosis and brucellosis. Being one of the most
potent emerging infections in India the clinicians and microbiologists
should be suspicious of this organism in any suppurative lesions at
multiple sites. Though B.pseudomallei has been most commonly reported
in diabetic and immune compromised hosts, immunocompetency does not
rule out its presence. All suspicious samples should be incubated for
5-7 days to isolate the organism. They should be treated for 10-14 days
as Intensive therapy in the hospital with sensitive intravenous
antibiotic followed by 3-6 months of oral therapy with Cotrimoxazole
for complete eradication.
Keywords:
Melioidosis, Burkholderia pseudomallei, Immunocompromised host.
Manuscript received:
04th April 2014, Reviewed:
13th May 2014
Author Corrected:
20th May 2014, Accepted
for Publication: 24th May 2014
Introduction
In 1911 Indian bacteriologist C.S. Krishnaswami, under the able
guidance of the pathologist Alfred Whitmore, described a
“Glanders-like” disease among the morphin addicts
in Rangoon, Burma [1, 2]. Melioidosis was coined from the
Greek words "melis," which means "distemper of asses," and "eidoes,"
which means "resemblance," by Stanton and Fletcher in
1932[3]. Since then, thousands of cases have been reported
all over the world, predominantly from Southeast Asian countries
(Thailand, Malaysia, Indonesia) and Australia. The causative agent has
been named variously since its identification by Alfred Whitmore;
Bacillus whitmori, Bacillus pseudomallei, Malleomyces pseudomallei,
Pseudomonas pseudomallei and since 1992, it has been called
Burkholderia pseudomallei [4]. The first report of melidosis from India
was by Rghavan et al from Mumbai in 1991[5]. Awareness of this disease
among the Indian clinicians and microbiologists is poor leading to the
under or mis diagnosis of the cases. Most of the cases of melioidosis
are wrongly diagnosed as tuberculosis, scrub typhus, leptospirosis and
brucellosis.
Epidemiology
In the latter half of the 20th century, melioidosis emerged as an
infectious disease of major public health importance in South East
Asian Region. Maximum cases of melioidosis have been reported from
Thailand where it is widely distributed in soil and in pooled surface
water such as in rice paddies. B. pseudomalleus is considered to have
potential in biological warfare, and is regarded as a potential
bioterrorist weapon. It appears on the category B list of the critical
agents published by the US Centers for Disease Control and Prevention
[6].
Melioidosis gained the lime light, when it was reported to be one of
the most potent emerging infections in India in 1996[7]. Since the
first case reported from Mumbai in 19991, about fifty cases of
melioidosis have been reported predominantly from southern part of
India. Though most of the cases have been reported from south India,
but actually they originated from the eastern and western coastal
belts. Maximum cases have been related to West Bengal where it seems to
be endemic. B. pseudomallei, like many other soil bacteria, is a
difficult organism to kill. It can survive in a variety of hostile
conditions like nutritional deficiency, acid and alkaline pH,
disinfectants, antiseptic solutions, exposure to many antibiotics, and
extremes of temperature [8]. There is a strong association between
monsoon rain, occupational and recreational exposure to surface muddy
water and melioidosis [8]. Other than rainfall, physical factors like
humidity, UV radiation, and temperature and chemical factors like soil
composition, other vegetation, and use of fertilizers may influence the
distribution of B. pseudomallei in the soil. The route of transmission
is by inhalation of contaminated dust or droplets, direct contact with
contaminated soil or water through penetrating wounds and existing skin
abrasions, aspiration of contaminated water, or ingestion [8]. In a few
cases, it is reported to be nosocomial, sexually transmitted, or
laboratory acquired.
Immunopathogenesis
After internalization, it escapes from endocytic vacuoles and spreads
from cell to cell for intracellular survival. It is resistant to
complement, lysosomal defensins, and cationic peptides, and produces
proteases, lipase, lecithinase, catalase, peroxidase, superoxide
dismutase, hemolysins, a cytotoxic exolipid and at least one
siderophore [9,10,11,12]. By virtue of all these above mentioned
features B. pseudomallei survives inside several eukaryotic cell lines
and is seen within phagocytic cells in pathological specimens
[12,13,14]. The cell wall lipopolysaccharide (LPS) and the highly
hydrated glycocalyx polysaccharide capsule of are important
determinants of virulence, which help to form slime, protect the
organism from antibiotic penetration, and alter the phenotypic
character of the organism, resulting in reduced susceptibility to
antibiotics [15,16,17,18]. The high mortality of B. pseudomallei
infections is related to an increased propensity to develop high
bacteremias (>1 cfu/ml) [19]. Septicemic melioidosis is
associated with very high concentrations of both pro-inflammatory and
anti-inflammatory cytokines - tumor necrosis factor (TNF),
interleukin-6, interleukin-10, interferon-gamma, and interleukin-18
[18,19,20,21]. The concentrations of interleukin-6 and interleukin-10
are independent predictors of mortality [21]. Antibodies against LPS
components have been demonstrated to be protective. Antibody level was
the highest for IgG (IgG1 and IgG2) [22]. Antibodies can persist
variably over 3 years.
Clinical feature
A number of risk factors for developing melioidosis have been
described; diabetes mellitus, thalassemia, renal disease, chronic lung
disease, chronic alcoholism, occupational exposure to soil and surface
water, elderly (>45 years) males, and immunosuppression due to
any cause [8]. Incubation period is usually 1-21 days, but can be as
long as months and even years [25]. A number of risk factors for
developing melioidosis have been described in various articles.
Patients with diabetes mellitus have been reported to have a causal
association with melioidosis. Other than that, risk factors like
thalassemia, renal disease, chronic lung disease, chronic alcoholism,
occupational exposure to soil and surface water, elderly (>45
years) males, and immunosuppressed state due to any cause may make the
population susceptible [8]. Incubation period is usually 1-21 days, but
can be as long as months and even years [25].
Clinical presentation of melioidosis varies widely. Clinical
presentation of melioidosis varies widely. It ranges from asymptomatic
infection, acute fulminant sepsis, sub acute multifocal abscesses to a
chronic mild infection [26]. Chronicity (symptoms persisting more than
2 months) has an incidence of about 11% [25] . Maximum cases
of chronic cases have been reported in Vietnam War experience described
as "Vietnam time-bomb," which manifested later in life as tuberculosis
like disease [6]. The most common presentation is community-acquired
pneumonia. However, many patients presenting with prolonged fever,
weight loss, and suggestive chest X-ray findings are misdiagnosed as
tuberculosis and may get antitubercular therapy. Other than that, there
are patients with septic arthritis, multiple abscesses in liver,
spleen, prostatic abscess (more in Australia), suppurative parotitis
(more in Thailand), osteomyelitis, pyomyositis, cellulitis, fasciitis,
skin abscesses or ulcers, and bacteremia with or without focus. On
radiograph, Swiss-cheese appearance of the deep-seated abscess in
liver, spleen, or in other organs is seen. Mortality rate in Indian
setup varies from 7 to 20% [27,28].
Laboratory diagnosis
The protean manifestations of melioidosis often lead to clinical
under-diagnosis of this fatal disease. Confirmation of melioidosis
relies heavily on clinical microbiology laboratories and specifically
on bacterial isolation by culture methods. Though Serological and
molecular methods have been evaluated in clinical settings, culture is
still considered the gold standard.
Culture of B. pseudomallei
Common specimens that yield B. pseudomallei on culture are blood, bone
marrow, pus, fluid aspirates, tissue, throat swab, sputum,
broncho-alveolar lavage (BAL) fluid, urine and ascitic fluid. Standard
specimen collection and transport principles are sufficient. Moreover,
overgrowth of commensals from non-sterile sites (sputum), suboptimal
selection of culture media, not using selective enrichment broth or
agar, dismissal of the growth as contaminating non-fermenters from
non-sterile sites, and discarding the culture plates by 3 days when the
growth of B. pseudomallei may take 5-7 days in many occasions makes the
diagnosis difficult. Blood and bone marrow cultures can be done using
conventional or automated blood culture system. Growth occurs within 5
days in conventional cultures and in 2 days in automated cultures.
Hence, extended incubation is not required [29]. All plates
are incubated at 35°-37°C for up to 5-7 days. Any
culture suspected of B. pseudomallei should be handled in class 2
biological safety cabinets (BSC II). Colonies are often small, smooth,
and creamy in the first 1-2 days on sheep blood agar, which gradually
change after a few days to dry and wrinkled colonies. Distinctive musty
or earthy odor is encountered while opening the Petri plates. Pink or
colorless colonies are seen on MacConkey agar after 1-2 days with
metallic sheen. After 3-4 days, the colonies may become dry and
wrinkled. Asdown’s media and modified
Asdown’s media has been described as the selective media
which contain tryptase soy agar with glycerol, crystal violet, neutral
red, and Gentamicin (4 mg/l). Colonies of B. pseudomallei on Ashdown
agar are pinpoint, clear, and pale pink at 24 h, changing to pinkish
purple, flat, and slightly dry with sheen in the next 2 days. After 5-7
days, the colonies get characteristic wrinkled appearance (rugose, or
cornflower head) and they take up crystal violet from the medium [30].
Rapid detection methods
Although a variety of rapid antigen detection methods have been
studied, none are commercially available yet. Among these, latex
agglutination is evaluated for identification of culture or blood
culture supernatants in Thailand and demonstrated sensitivity 95.1-100%
and a specificity of 99.7-100% [31]. Similar results are shown in a
study from Vellore using in-house co-agglutination test and latex
agglutination test [32]. In Thailand, the results of rapid
immunofluorescence (IF) test and those of an existing IF method were
prospectively compared with the culture of various clinical specimens
from patients with suspected melioidosis. The sensitivities of both IF
tests were 66% and the specificities were 99.5 and 99.4%, respectively
[33].
Antibody detection
Indirect hemagglutination assay (IHA) remains the most widely used test
despite its poor sensitivity and specificity in acute cases due to
background seropositivity as a result of environmental exposure in
endemic areas. These facts have limited the diagnostic utility of IHA
in acute melioidosis. Immunochromatographic tests have also
demonstrated similar results and presented an enhanced performance over
IHA [34]. Enzyme-linked immunosorbent assays (ELISAs) used on
affinity-purified antigen, crude antigen, LPS, and extracellular
polysaccharide (EPS) have been validated in clinical context with
varied ranges of sensitivity (63.9-82.4%) and specificity (71.1-82.1%)
[35]. Overall, IgG detection and not IgM appears to be a more sensitive
indicator of clinical disease [36].
Molecular diagnosis
Delay in obtaining the culture results and inability of the serological
methods in achieving accurate diagnosis have led to the search for
accurate and rapid tools such as polymerase chain reaction (PCR).
Primers targeting 23S rRNA, 16S rRNA, and 16S and 23S RNA junction and
TTS1 gene have been evaluated both on bacterial cultures and clinical
specimen. All PCR protocols showed accurate results in confirming the
bacterial isolate after culture, while their sensitivity and
specificities varied on testing the clinical specimen directly. Low
number of bacteria in blood specimen, presence of PCR inhibitors in
blood, and probable latency of the bacterium within macrophages without
an active disease are the possible explanations. Overall, molecular
detection is still not superior to culture in case of B. pseudomallei
at this point of time [37].
Treatment
In the medical wards, especially in the medical Intensive Care Units
(ICUs), the usual practice of the physicians is to initiate treatment
with beta-lactam - beta-lactamase inhibitors (BL-BLIs). These
combinations are not recommended for the treatment of melioidosis, but
may, to some extent, decrease the bacterial load. However, the patient
may come back with relapse [30]. A similar scenario is encountered with
surgical speciality, where the most common antibiotic used after
drainage of any abscess is Amoxicillin-Clavulanic acid.
Amoxicillin-Clavulanic acid is one of those antibiotics which showed
high resistance with melioidosis [30]. Even after the microbiological
confirmation and recommendation of the proper treatment, it is found
that the treating clinician does not follow the recommendation, as the
patient showed clinical improvement with other antibiotics. Melioidosis
may have a protracted course and a chance of relapse if proper
antibiotic treatment is not continued for an adequate period of time.
The bacteria are inherently resistant to many antibiotics that are
commonly used against Gram-negative non-fermenters - like Penicillin,
Ampicillin, first generation and second generation cephalosporins,
Gentamicin, Tobramycin, Streptomycin, and Polymyxin. Ertapenem,
Tigecycline, Moxifloxacin, Tetracyclines, Chloramphenicol, the
quinolones, and Ceftriaxone, do not appear to be clinically useful in
the intensive phase [8]. The treatment of melioidosis is divided into two phases: Intensive
phase, consisting of in-patient treatment for at least 10-14 days with
Ceftazidime or Carbapenems (Imipenem or Meropenem) and Eradication
phase, consisting of treatment with oral Trimethoprim- Sulfamethoxazole
(TMP-SMX) for 3-6 months [30]. Though the conventional intensive
regimen consists of I/V Ceftazidime or Carbapenams with oral Doxycyclin
or Cotrimoxazole, a recent study proves no significant difference in
single versus combination therapy [26].
Prevention
Melioidosis is a preventable disease. Tourists traveling to endemic
areas should be properly cautioned against barefoot walking and
recreational activities in water. People with risk factors should be
guided to take proper precautions like protective footwear and mask
during rainy season and while going to the paddy fields. Laboratory
technicians and research workers should work in inside BSC II facility,
and should not try to sniff the colonies from the culture plates. There
is no human vaccine available so far. However, there are researches in
animal models involving the use of live attenuated, subunit,
plasmid-based DNA, and killed whole-cell vaccine [30].
Road to future
Melioidosis in India is like tip of iceberg. It is known to be one of
the most potent emerging infections in our country so at any time there
may be an epidemic of melidiosis. Both the clinicians and the
microbiologist have to be suspicious to diagnose the cases. Regular
interactions among them should be arranged at national level. There
should be a central reporting system and a surveillance team. At
present the Department of Microbiology, Kasturba Medical College,
Manipal is taking initiatives to bring all the interested researchers
under one umbrella [30]. Moreover, it may play a role of a reference
laboratory in future, where bacterial strains can be sent for
confirmation after presumptive diagnosis is made in the respective
institutions. So definitely a long way to go.
Funding: Nil,
Conflict of interest: Nil
Permission from IRB:
Yes
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How to cite this article?
Karuna T, Khadanga S, Dugar D. Melioidosis: Indian perspective. Int J
Med Res Rev 2014;2(3):243-248. doi:10.17511/ijmrr.2014.i03.013