The monsoon season brings with it a much-needed break from the scorching
summer sun, a canopy of greenery to the otherwise barren hills surrounding
the city, and unfortunately, a host of diseases. Among these, dengue
(pronounced den-gee, and not den-goo) is one of the most dreaded.
According to a WHO estimate, approximately one third of the population of
the world lives in areas where dengue is endemic- which means that around
2.5 billion people are constantly in danger of acquiring the infection. Around
50 million of these will contract the infection, and approximately 25,000
people will die from the infection every year.
India has seen a steady rise in dengue infections from 2001 onwards, with
states like Maharashtra, Karnataka, Tamil Nadu, Pondicherry, Delhi, Haryana,
Rajasthan and Chandigarh accounting for the major disease burden. With the
spread of urbanization, states like Mizoram, Odisha and Arunachal Pradesh
have also reported dengue infections, where the disease was previously non-
Though the origin of the unusual name of the disease remains unclear, one
popular theory states that the word ‘dengue’ is derived from the Swahili word ‘ka-dinga pepo’, which translates to ‘cramp-like seizure caused by an evil spirit’
or ‘Devil’s disease’! As the name suggests, severe muscle and joint pain is one
of the typical symptoms of dengue. Clinically, symptoms of dengue vary from
mild flu-like illness with headache, fever with rash, respiratory symptoms, to
bleeding, and multi-organ failure.
Dengue spreads from person-to-person by the means of a mosquito vector.
Aedes aegypti and Aedes albopictus are species of mosquitoes that spread the
dengue virus. This species of mosquitoes also transmits chikungunya and zika
virus. These mosquitoes bite during the early morning and late evening hours.
When the mosquito bites an infected person, the virus enters the mosquito
and multiplies. Disease spread occurs when the mosquito carrying the virus
bites or takes a blood meal from another person, thereby injecting the virus
into that person. Aedes mosquitoes lay their eggs in water. Indoor water
sources like water collected in bowls, pots, tyres, vases, fountains, etc, which
commonly happens during the monsoons, serve as an excellent source for the
mosquitoes to lay their eggs. A small amount of water is enough for the eggs to
develop into larvae, and then into pupae and adults.
An infected mosquito carries the virus throughout its life and can also pass on
the virus to its progeny.
The answer lies in the different serotypes of the virus. Serotypes are closely
related variants of the same virus. The dengue virus has four different
serotypes: DEN-1, DEN-2, DEN-3 and DEN-4. If a person acquires the infection
for the first time with one of the serotypes, the body develops immunity
against that particular serotype of dengue virus. The patient usually develops
only mild symptoms and makes a full recovery. Subsequently, however, if the
patient acquires the infection from a different serotype, the body only partially
recognises the virus, and this type of immune response actually ends up
attacking the patient’s own tissues and organs, instead of attacking the virus.
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Therefore, a second dengue infection with a different viral serotype results in a
more severe infection.
Various tests are available to diagnose a dengue infection. During the acute
phase or the initial 4-5 days of dengue infection, a viral antigen called NS1 can
be detected in blood samples. NS1 detection can be done via rapid tests which
have a lower sensitivity and specificity or by a method known as ELISA, which
though slightly more time consuming is more accurate. In certain cases NS1
may be detectable for duration slightly longer than five days.
Dengue virus PCR can directly detect the viral RNA in the blood, within the first
few days of symptom onset. This test can be positive in as little as 24 hours
after onset of symptoms. The limiting factor for dengue virus PCR is the cost
and the need for batching, which means the result will take longer. One
important advantage of the dengue PCR test is its ability to detect the viral
RNA from cerebrospinal fluid in suspected cases of dengue affecting the brain.
After the initial phase, dengue virus specific antibodies can be detected in the
blood. The IgM antibody is detectable after around 7 days and remains in the
blood till 21 days. The IgG antibodies are detectable in the third week of
infection, and are mostly useful for detecting an infection in the past, rather
than a current infection. IgM and IgG antibodies can be detected by ELISA. M
and G ‘capture’ ELISAs are superior to other ELISAs available and are used in
most of the standard diagnostic laboratories. If you test positive for dengue, please consult your doctor. Some more laboratory tests may be required.
The other monsoon fevers to be considered in the differential diagnosis of
dengue are malaria, chikungunya and zika virus infections. It is advisable to
perform all these tests to identify the cause of monsoon fevers.
Dengue infection can be prevented by taking some simple measures.
Though there are no specific drugs or vaccines available against dengue in
India at the present time, they may become available in the near future. For
dengue infection, since no virus specific cure is available, prevention is indeed