Editorial
The curse of dengue
Indian J Med Res 124, November 2006, pp 467-470
Dengue fever (DF) and dengue haemorrhagic
fever (DHF) have arrived to stay with vengeance in
this country. Is it unexpected? No, we are not
surprised as all the risk factors that promote spread
of dengue virus (DV) are present here, and in plenty.
The risk factors for DF/DHF are infestation with
Aedes mosquito, hot and humid climate promoting
mosquito breeding, mosquito density, the water
storage pattern in the houses, population density and
large movement of people towards urban area1. This
country has witnessed extensive construction work,
for houses, malls, national highways network and
special economic zones. These activities result in
dumping of construction and demolition materials
forming small pits and pockets for rain water
collection. Due to erratic and scantly water supply
the households are forced to store portable water in
containers without a lid thus providing ideal sites for
Aedes breeding. Dengue viruses are of four serotypes
(1 to 4) and the presence of more than one serotype
in a population is a risk factor for DHF. The cocirculation
of multiple DV serotypes in the same
region has been a common knowledge in several
countries including India. Using a modified multiplex
reverse transcription-polymerase chain reaction
assay, concurrent infections by two different
serotypes of dengue virus have been shown to occur
in the same patient2. Such concurrent infections by
two dengue viruses may also increase the severity of
the disease2. Genotypic studies have shown that the
more virulent Asian strain of DV is different from
the milder American strain which suggest a role for
viral genetics in DHF3. Emergence and re-emergence
of DF and DHF continue to be a global challenge.
The evolution of genetics of hosts, pathogens and
vectors have been phenomenal and the extensive
growth of genetic studies over the years has greatly
increased our understanding of the transmission and
pathogenicity of infectious diseases. The profound
influence of the host’s genetic make-up on resistance
and susceptibility to DHF has been established in
numerous studies4.
Dengue is found in tropical and sub-tropical
regions around the world, predominantly in urban
and semi-urban and now in rural areas also. Humans
are the main amplifying host of the virus. Recovery
from infection by one type of DV provides lifelong
immunity against that serotype but confers only
partial and transient protection against subsequent
infection by the other three. Halstead5 described
antibody-dependent enhancement (ADE) of
infection, in which DV uptake and replication in
macrophage is increased by immune sera (IgG), and
this phenomenon has later been observed for a
number of viruses6. The sequential infection
increases the risk of DHF specially if infection with
DV-1 is followed by DV-2 or DV-31. Viral virulence
and immune responses have been considered as two
major factors responsible for the pathogenesis of
DHF. Virological studies are attempting to define
the molecular basis of viral virulence7,8. The
immunopathological mechanisms appear to include
a complex series of immune responses. A rapid
increase in the levels of cytokines and chemical
mediators apparently plays a key role in inducing
plasma leakage, shock and haemorrhagic
manifestations9,10. It is likely that the entire process
is initiated by infection with a so called virulent
dengue virus, often with the help of enhancing
467
antibodies in secondary infection, and then triggered
by rapidly elevated cytokines and chemical
mediators produced by intense immune activation.
However, understanding of the DHF pathogenesis
is not complete.
The first major epidemic illness that was clinically
compatible with dengue occurred in Madras (now
Chennai) in 1780 and later on spread to all over the
country. DV was first isolated in Japan in 1943 and
one year later at Calcutta in 1944 from the blood of
US soldiers. DHF was first recognized in 1950s during
the dengue epidemics in the Philippines and Thailand
and quickly spread to other parts of the world11. Only
nine countries had DHF epidemics before 1970. The
prevalence of dengue has grown dramatically and the
disease is now endemic in more than 100 countries in
Africa, the Americas, the Eastern Mediterranean,
Southeast Asia and the Western Pacific, the last two
are most seriously affected. Extensive epidemics of
DF occurred in India, the early ones were at Calcutta
and south India in 196312,13. Then DF became endemic
all over India14,15. DHF was present in the neighbouring
countries for a long time but the first extensive
epidemic of DHF occurred only during 1996 in the
northern India16,17. One does not know what prevented
it from coming to this country till 1996 as all the risk
factors were present.
Some 2500 million people - two fifths of the
world’s population - are now at risk from dengue.
According to the WHO estimates made in 2002 there
may be 50 million cases of dengue infection
worldwide every year. An estimated 500,000 cases
of DHF require hospitalization each year, of whom
a very large proportion are children18,19. The year
2001 witnessed unprecedented global dengue
epidemic activity in the American hemisphere, the
Pacific islands and continental Asia. During 2002,
more than 30 Latin American countries reported
over 1000000 DF cases with large number of DHF
cases2,18. Over the past two decades, DV type 3 has
caused unexpected epidemics of DHF in Sri Lanka,
East Africa and Latin America. Isolates from these
geographically distant epidemics are closely related
and belong to DV serotype 3, subtype III, which
originated in the Indian subcontinent. The
emergence of DHF in Sri Lanka in 1989 correlated
with the appearance of a new DV serotype 3,
subtype III variant which forms genetically distinct
group19.This variant spread from the Indian
subcontinent into Africa and from there into Latin
America in the mid 1990s20. The 1996 epidemic in
India was mainly due to DV serotype 216,17 but since
2003, epidemics appear to be mainly due to DV
serotype 3, subtype III21. The present DHF epidemic
(during 2006) in India appears mainly due to DV
serotype 3, though other serotypes are also present.
Early diagnosis of DV infection is important and
can be established with easily available laboratory tests.
Increased haematocrit value (>20%) and a positive
tourniquet test indicate that the patient should be under
close surveillance for early signs of DHF while negative
test does not rule out dengue infection. Low platelet
counts do not predict clinically significant bleeding in
dengue. It follows that platelet or blood transfusions
should not be administered based upon platelet count
alone. DHF or dengue shock syndrome cases frequently
have compensated consumptive coagulopathy that
seldom requires treatment. Bleeding is most likely
caused by activated platelets resulting from damaged
capillary endothelium. There is no specific treatment
for dengue fever. However, careful clinical management
frequently saves the lives of DHF patients. With
appropriate intensive supportive therapy, mortality may
be reduced to less than 1 per cent.
Vaccine development for dengue and DHF is
difficult because any of four different viruses may
cause disease, and because protection against only
one or two dengue viruses could actually increase
the risk of more serious disease. However, efforts
are being made for the development of vaccines that
may protect against all four dengue viruses. Several
promising vaccine candidates in the form of live
attenuated and chimeric vaccines have been
developed and are currently in human clinical trials.
However, significant practical, logistic, and scientific
challenges remain before these vaccines can widely
468 INDIAN J MED RES, NOVEMBER 2006
and safely be applied to vulnerable populations6.
Dengue continues to be a global challenge because
the pathogenesis of DHF is not fully understood,
there is no immediate prospect of a vaccine and the
mosquito control measures are inadequate. In absence
of a vaccine or drug, the dengue disease can be
managed successfully by preventing serious illness
through patient follow up and monitoring danger
signals so that aggressive intravenous rehydration is
initiated to prevent shock and complications, such
as massive haemorrhage and disseminated
intravascular coagulation, etc. At present, the only
method of controlling or preventing DF and DHF is
to combat the vector mosquitoes. The wide-spread
DHF epidemics reinforce the belief that DHF has
come to stay in this country and will continue to
spread to newer areas unless mass education on the
vector control measures in and around households
are taken up on war footing.
U.C. Chaturvedi
201-Annapurna Apartments
No. 1, Bishop Rocky Street
Faizabad Road
Lucknow 226007, India
e-mail: ucc05@rediffmail.com;
uchaturvedi@yahoo.com
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