Dengue: a newly emerging viral infection in Andaman and
Nicobar Islands, India
I. K. CHAAITHANYA1, D. BHATTACHARYA1, N. MURUGANANDAM1,
R. THAMIZHMANI1, B. V. SURESH BABU2, S. G. SUNDARAM1, M. MATTA3,
S. S. SINGH4AND P. VIJAYACHARI1*
1Regional Medical Research Centre (ICMR), Port Blair, Andaman and Nicobar Islands, India
2King Institute of Preventive Medicine, Guindy, Chennai, India
3INHS Dhanwantari Hospital, Port Blair, Andaman and Nicobar Islands, India
4G. B. Pant Hospital, Port Blair, Andaman & Nicobar Islands, India
(Accepted 3 November 2011)
Prior to 2009 dengue fever had not been reported in the Andaman and Nicobar archipelago. In
2009, a few patients with dengue fever-like illness were reported, some of whom tested positive
for dengue antibodies. In 2010, 516 suspected cases were reported, including some with dengue
haemorrhagic fever (DHF) and dengue shock syndrome (DSS); 80 (15.5%) were positive for
dengue antibodies. DENV RNA was detected in five patients and PCR-based typing showed that
three of these belonged to serotype 1 and two to serotype 2. This was confirmed by sequence
typing. Two clones of dengue virus, one belonging to serotype 1 and the other to serotype 2
appeared to be circulating in Andaman. Emergence of severe diseases such as DHF and DSS
might be due to recent introduction of a more virulent strain or because of the enhancing effect of
sub-neutralizing levels of antibodies developed due to prior infections. There is a need to revise
the vector-borne disease surveillance system in the islands.
Key words: Andaman and Nicobar Islands, dengue fever, dengue serotypes.
Dengue has emerged as a global health problem, as
evidenced by a series of epidemics throughout the
tropical and subtropical regions of the world .
Dengue fever (DF) and dengue haemorrhagic fever
(DHF) are the most important arboviral diseases in
terms of both morbidity and mortality. Dengue virus
(DENV) belongs to the genus Flavivirus, family
Flaviviridae, with four serologically related but anti-
genically distinctive serotypes (DENV-1, -2, -3, -4) .
These serotypes induce a spectrum of illness, ranging
from uncomplicated febrile illness to severe and fatal
syndromes such as DHF and dengue shock syndrome
Andaman and Nicobar Islands is an archipelago of
more than 500 islands and islets, stretching over
700 km from north to south, in the Bay of Bengal.
There are 38 inhabited islands with a population of
about 380000 . Prior to 2009 dengue had not been
reported in Andaman and Nicobar archipelago ,
although antibodies against dengue virus (DENV-2)
have been detected in the population . In 2009, a
few clinical suspected cases were reported by the
health services, some of which tested positive for IgM
anti-DENV antibodies. An entomological survey in
* Address for correspondence: Dr P. Vijayachari, Regional
Medical Research Centre (ICMR), Post Bag No. 13, Port Blair
744101, Andaman and Nicobar Islands, India.
Epidemiol. Infect., Page 1 of 5.
f Cambridge University Press 2011
mosquitoes in Port Blair . A large outbreak of an-
other Aedes mosquito-borne disease, chikungunya
fever, occurred in South Andaman in 2006 .
During June–August 2010, a number of patients
with DF-like febrile illness attended G. B. Pant
Hospital, the only referral hospital in the Islands, and
other healthcare facilities in Port Blair town situated
in South Andaman Island. Investigations were con-
ducted to identify and characterize the aetiological
agent. A case definition for suspected DF was made
based on the symptoms/signs listed in World Health
Organization’s guidelines . According to the case
definition, any patient with acute febrile illness associ-
ated with headache, retro-orbital pain, rash, muscle
case of DF. Although the WHO case definition man-
dates the presence of at least two from a list of symp-
as haemorrhagic manifestations and leucopenia for a
diagnosis of a probable case, we used a more inclusive
case definition that mandated presence of any one of
sensitivity. All patients who attended G. B. Pant Hos-
pital and a childcare hospital in Port Blair and fulfilled
the case definition were included in the study. Blood
of reporting to the hospital.
The study was approved by the institutional ethics
committee of the Regional Medical Research Centre
All the samples were tested for the presence of anti-
DENV and anti-chikungunya virus (CHIKV) IgM
antibodies by IgM capture ELISA kits developed by
the National Institute of Virology (NIV), Pune . A
subsample of the patients who reported to the hospital
within 4 days of onset of symptoms and were negative
for IgM anti-DENV antibodies was also tested for
DENV RNA by reverse transcription – polymerase
chain reaction (RT–PCR) followed by nested PCR for
detection of serotype. RNA was extracted from the
the standard protocol . The first-round PCR
C and pre-M regions of the viral genome followed by
nested multiplex PCR to differentiate between the
was specific to each of the four serotypes of DENV.
The 511-bp fragments amplified in the first-stage
PCR were purified with QIAquick PCR purification
showed widespreadinfestation ofAedes
kit (Qiagen) and sequenced using the Big Dye
Terminator Cycle Sequencing kit (Applied Biosys-
tems, USA) according to the manufacturer’s instruc-
tions. All DNA sequences were assembled using
SeqMan II version 5.03 (DNASTAR, USA). These
sequences were then aligned with previously pub-
lished sequences of DENV strains belonging to vari-
ous combinations of serotypes and genotypes by the
Clustal W multiple alignment and pair-wise alignment
program of MEGA software suit (version 4). Genetic
parameter algorithm and a phylogenetic tree was
constructed by the neighbour-joining method .
The statistical significance of the relationships ob-
tained was estimated by bootstrap resampling analy-
sis (1000 repetitions). In addition, the aligned DNA
sequences were BLAST-searched to assess their
identity with previously characterized sequences of
the DENV genome.
During the period between March and December
2010, a total of 516 patients fulfilling the case defi-
nition criteria attended the two hospitals. Blood
samples of all these patients were tested by DENV
IgM capture ELISA and 80 (15.5%) were positive.
Distribution of cases by month of reporting showed a
large peak in July–August, when 321 (62.2%) of the
516 suspected cases and 60 (75%) of the 80 confirmed
cases occurred. None of the samples was positive
for CHIKV IgM antibodies. Of the 80 confirmed
cases, 26 (32.5%) were aged <5 years and 48 (60.0%)
were aged <15 years. Although suspected patients
were diagnosed at the hospitals at Port Blair,
some were referred from other islands such as Middle
Andaman (n=5), Little Andaman (n=1) and Car
Nicobar (n=2). None of the confirmed cases had a
history of travel outside the islands.
One hundred and nine samples negative by IgM
capture ELISA were processed by RT–PCR and five
(4.6%) showed amplification of the 511-bp fragment
common to all serotypes of DENV. All five of the
samples were from patients residing in the main island
of South Andaman. Three of these also showed am-
plification of the 482-bp fragment specific to DENV-1
and the remaining two showed amplification of the
119-bp fragment specific to DENV-2, indicating that
both DENV serotypes 1 and 2 exist in the islands.
The NCBI BLAST search result showed that the
sequences of the three strains that showed amplifi-
cation of the 482-bp fragment specific to DENV-1
(DG/PB 18, DG/PB 06, DG/PB 15) had 96–98%
homology with DENV serotype 1 sequences while the
2I. K. Chaaithanya and others
AY037116 AUSTRALIA COSMOPOLITAN
EF051521 CHINA COSMOPOLITAN
DF/PB 03 serptype 2
DF/PB 01 serotype 2
DQ448232 INDIA(GWL) COSMOPOLITAN
AB189126 DENV-3 Genotype-1
AB189127 DENV-3 Genotype-1
AY679147 DENV-3 GENOTYPE-3
DG/PB 18 SEROTYPE-1
DG/PB 06 SEROTYPE-1
DG/PB 15 SEROTYPE-1
Fig. 1. Phylogenetic neighbour-joining tree showed three Andaman DENV sequences (DG/PB 18, DG/PB 06, DG/PB 15)
have been grouped with DENV serotype 1 as well as genotype 3 and the other two sequences of Andaman DENV (DF/PB 03,
DF/PB 01) grouped with DENV serotype 2 of genotype 1.
Emerging dengue infection in Andaman and Nicobar Islands3
sequences of the two strains that showed amplifi-
cation of the 119-bp fragment specific to DENV-2
(DF/PB 03, DF/PB 01) had 92–98% homology with
the DENV serotype 2 sequences available in the
database, thus further confirming the existence of
dengue serotypes 1 and 2 in the islands.
In the phylogenetic tree (Fig. 1), our DENV-1 se-
quences (DG/PB 18, DG/PB 06, DG/PB 15) and
DENV-2 sequences (DF/PB 03, DF/PB 01) formed
subclusters under the DENV serotype 1 cluster and
the DENV serotype 2 cluster, respectively. The mean
genetic distances between Andaman DENV-1 and
worldwide DENV-1 (0.035) as well as between
Andaman DENV-2 strains and worldwide DENV-2
(0.069) were very small. The Andaman DENV-1
subcluster showed close relatedness to genotype 3
while the Andaman DENV-2 subcluster showed close
relatedness to the cosmopolitan genotype.
Dengue occurrence in India has shown a substan-
tial increase from previous years with more than
28000 cases reported by the National Vector-Borne
Disease Control Programme (NVBDCP). Outbreaks
have been reported in many places including Delhi
and Tamilnadu in July–August . The present
study conclusively shows the presence of DENV sero-
types 1 and 2 in Andaman. Antibody-dependent en-
hancement (ADE) of infection has been postulated to
cause severe and fatal complications in dengue viral
infections such as DHF and DSS . ADE occurs
when a patient who was previously infected with one
serotype of the virus and has sub-neutralizing levels of
antibodies, becomes re-infected with a different sero-
type. The existence of multiple serotypes in the region,
therefore, may pose a high risk of DHF and DSS.
Viral factors including structural differences 
have also been implicated in the development of DHF
and DSS . The introduction of the South East
Asian genotype of DENV-2 is believed to have caused
epidemics of DHF in the Americas in the 1980s .
Intra-epidemic evolution of the circulating virus has
been postulated to increase the severity of the disease
as epidemics progress. Research so far appears to in-
dicate that viral virulence factors and detrimental host
responses are collectively responsible for the increased
vascular permeability that occurs in DHF and
Serologically confirmed DF was first detected in the
islands in 2009, although dengue antibodies were de-
tected in an earlier population-based study . In
2010 a few clinically suspected cases of DHF and DSS
were reported. Dengue viral infection could have been
occurring in Andaman Islands silently during the past
few years as has been reported to have occurred in the
South Pacific Islands . There is a possibility that a
new viral strain has been introduced to the islands
recently and because of either a higher virulence of the
strain or the enhancing effect of the sub-neutralizing
levels of antibodies present in the population due to
prior unnoticed infection in the past, or both, severe
clinical forms are now starting to emerge.
The present study is a strong signal that DF is
emerging as an important public health problem in
these islands. Aedes mosquito infestation is wide-
spread in the islands and there is a strong likelihood
that outbreaks will emerge in the future. The existence
of multiple serotypes of the virus in the islands
increases the risk of DHF and DSS and therefore,
future dengue outbreaks could lead to increased
morbidity and mortality. The vector-borne diseases
surveillance system in these islands needs to be revised
and vector surveillance should be given top priority as
vector-control measures are the only available pre-
ventive measures for dengue. The public health sys-
tem including patient care facilities needs to be
prepared to respond to any future dengue outbreak
where a larger proportion of cases might develop se-
vere complications such as DHF and DSS.
This study was supported by a grant from the Indian
Council of Medical Research (No. 5/8/7/16/2010-
ECD-I). The authors thank Dr P. Gunasekaran of
King Institute of Preventive Medicine for his valuable
suggestion regarding the work. The authors are also
grateful to CEO of INHS Dhanwantari, and the
Directorate of Health Service (Andaman & Nicobar
Islands) for their extensive support and help during
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