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Kolkata is reeling under its worst bout
of dengue this monsoon season. Many people have succumbed to the infection and
government and private hospitals are flooded with dengue patients. (1) The city is facing
one of its worst dengue outbreaks in recent times.
Nine-year old Sreeja Das was the first dengue victim in
the state. The epidemic first struck in the second week of August. Several people in and around Kolkata have
been hospitalized since then with symptoms similar to dengue. Many patients have died
from the disease and the number of confirmed cases has gone up to 638 (2) and still counting.
Dengue is a Public Health Menace which is
better prevented rather than being treated as is the case with all diseases.
There has been a recent surge in Dengue cases
not only in Kolkata, but in various other parts of the world as well. The incidence of dengue has grown dramatically around
the world in recent decades. Over 2.5 billion people (i.e. over 40% of the
world's population) are now at risk from dengue. WHO currently estimates that
there may be 50–100 million dengue infections worldwide every year (3) .
Dengue also known as breakbone fever, is an infectious tropical disease caused by the dengue virus (4) . There are four distinct, but closely
related, serotypes of the virus that cause dengue (DEN-1, DEN-2, DEN-3 and
DEN-4). Recovery from infection by one provides lifelong immunity against that particular
serotype. However, cross-immunity to the other serotypes after recovery is only
partial and temporary. Subsequent infections by other serotypes increase the
risk of developing severe dengue (3) .
Dengue is transmitted by the Aedes aegypti mosquito which is the primary vector
of dengue. The virus is transmitted to humans through the bites of infected
female mosquitoes. 4–10 days after getting infected, a mosquito is capable of
transmitting the virus for the rest of its life. Infected humans are the main
carriers and multipliers of the virus, serving as a source of the virus for
uninfected mosquitoes (3) .
The Aedes
aegypti mosquito lives in
urban habitats and breeds mostly in man-made containers. Ae. aegypti is a daytime feeder; its peak biting
periods are early in the morning and in the evening before dusk. Female Ae.
aegypti bites multiple people
during each feeding period (3) .(Also called
Fearless Day Biter.)
The rapid transmission of the dengue virus this year
in Kolkata has led experts to believe that a new vector is stalking the city along
with the primary carrier Aedes aegypti, especially in Salt lake, the fringe
areas of the city and along the EM Bypass where hundreds have been infected.
Aedes albopictus or the Asian tiger mosquito is a secondary vector of the
dengue virus and as lethal as the Aedes aegypti. (5) . Aedes albopictus has also spread
to North America and Europe largely due to the international trade in used
tyres (a breeding habitat) and other goods (e.g. lucky bamboo). Ae. albopictus is highly adaptive and therefore can
survive in cooler temperate regions of Europe. Its spread is due to its
tolerance to temperatures below freezing, hibernation, and ability to shelter
in microhabitats (3) .
Rampant construction activities and
chopping of trees along the Bypass (Kolkata) are responsible for a spurt in the
number of tiger mosquitoes this year. The albopictus prefers old buildings and
tree crevices. With buildings being pulled down for high-rises and trees being
chopped to make way for the Garia-Dum Dum Metro corridor along Bypass, the
secondary vector has turned active. More than 1500 trees have been felled along
the Bypass since 2010 to make way for Metro pillars. Green activists believe
this has upset the ecosystem of the area and contributed to the spread of
diseases like malaria and dengue (5) .
Albopictus mosquito rests in the
vicinity of human dwellings. They tend to move into houses quicker than other
vectors and are hence more difficult to eliminate (5) .
A case of dengue may present
as (6) :
- Classical dengue fever
- Dengue haemorrhagic fever
- Dengue shock syndrome
Classical dengue fever:
Dengue fever can occur in epidemics which often start during the rainy
season when the breeding of the vector mosquitoes is
generally abundant.
All ages and both sexes are susceptible to dengue fever.
Children usually have a
milder disease than adults.
The onset of the disease is sudden with chills
and high fever, intense headache,
muscle and joint
pains. There may be pain behind the eyes (Retro orbital pain).
Other common
symptoms include extreme
weakness, anorexia, constipation, altered taste
sensation, pain in abdomen, sore
throat and general depression.
Fever
is usually between 39°C
and 40°C and is associated with
generalized pain and a headache; this usually lasts two to seven days. At this stage, a rash occurs in 50–80%
of those with symptoms. It occurs in the first or second day of symptoms as flushed skin, or later in the course
of illness (days 4–7), as a measles-like rash (4) . The Rash starts on
the chest and back and may spread to the extremities and rarely to the
face. It may be accompanied by
itching and hyperaesthesia. The rash
lasts for 2
hours to several
days and may be
followed by desquamation (6) .
Recovery is
usually complete (6) .
Dengue haemorrhagic fever:
Dengue haemorrhagic fever (DHF)
is a severe form of dengue fever, caused by infection with more than one
dengue virus. The severe illness
is thought to be due
to double infection with dengue
viruses - the first infection probably sensitizes the patient, while the second
appears to produce an immunological catastrophe. It presents with the
following clinical manifestations :
(a) Fever -
acute onset, high,
continuous, and lasting
2 to 7 days.
(b) Haemorrhagic
manifestations like petechiae, purpura, ecchymosis, epistaxis, gum bleeding haematemesis
and/or melaena.
(c) Enlargement of
liver.
Blood examinations reveal Thrombocytopenia (Platelet
count 100,000/mm3 or less).
And Haemoconcentration (haemotocrit increased by 20 per
cent or more of base-line value.)
Dengue shock syndrome (DSS): It is
DHF (Dengue Haemorrhagic fever) plus Shock-manifested by rapid and weak pulse
with narrowing of the pulse
pressure (20 mm Hg or
less) or hypotension, with the presence of cold,
clammy skin and restlessness.
The diagnosis of dengue is typically
made clinically, on the basis of reported symptoms and physical examination. A
doctor should be consulted immediately if any of the symptoms as mentioned
above appears especially in as endemic area or if the zone is under an ongoing
epidemic. The warning signs of Dengue
involve Abdominal pain Ongoing vomiting, Liver enlargement, Mucosal bleeding, High hematocrit with
low platelets and lethargy (7) .
The diagnosis should be considered in
anyone who develops a fever within two week of being in the tropics or subtropics.
The earliest change detectable on laboratory investigations is a low white
blood cell count, which may then be followed by low platelets and metabolic
acidosis (4) .
Dengue fever may be diagnosed by
microbiological laboratory testing (7) . This can be done by
virus isolation in cell
cultures, nucleic acid
detection by PCR, viral antigen detection or specific antibodies (serology) (8) . Virus isolation and nucleic acid
detection are more accurate than antigen detection, but these tests are not
widely available due to their greater cost (7) . All tests may be negative in the early
stages of the disease (8) . PCR and viral antigen detection are
more accurate in the first seven days (9) .
There are no specific
treatments for dengue fever. Treatment
depends on the symptoms, varying from oral
rehydration therapy at home with
close follow-up, to hospital admission with administration of intravenous fluids and/or blood transfusion (4) . A decision for
hospital admission is typically based on the presence of the "warning
signs" discussed above, especially
in those with preexisting health conditions.
Dengue Shock Syndrome is a medical emergency that requires
hospitalization with prompt
and vigorous volume
replacement therapy (6) . Blood transfusion
is initiated early in patients presenting with unstable vital signs in the face
of a decreasing hematocrit, rather than waiting for the hemoglobin
concentration to decrease to some predetermined "transfusion trigger"
level (7) .
The juice of the papaya leaf has been seen to arrest the
destruction of platelets that has been the cause for so many deaths from dengue. Chymopapin and
papin - enzymes in the papaya leaf - help revive platelet count. The
juice has to be prepared from fresh papaya leaves (10) .
Prevention of Dengue infection depends on
control of and protection from the bites of the mosquito that transmits it.
The vectors of DF
and DHF (e.g.,
A. aegypti) breed
in areas around houses and, in
principle can be controlled by individual and community action, using various mosquito
control measures (6) . (The primary method
of controlling A. aegypti is by eliminating its habitat. This is done by emptying containers of
water or by adding insecticides or biological control agents to these areas.
The
personal protection measures
are like that of wearing of full sleeve shirts and
full pants; use of mosquito
repellent cream; liquids,
coils, mats etc.; use
of bed-nets for
sleeping infants and young children during day time to prevent
mosquito bites. So far, there
is no satisfactory
vaccine and no
immediate prospect of preventing the disease by immunization. (6) .
The World Health Organization recommends
an Integrated Vector Control program consisting of five elements to fight this
menace:
- Advocacy, social mobilization and legislation to ensure that public health bodies and communities are strengthened,
- collaboration between the health and other sectors (public and private),
- an integrated approach to disease control to maximize use of resources,
- evidence-based decision making to ensure any interventions are targeted appropriately
- capacity-building to ensure an adequate response to the local
situation
