DENGUE VIRUS - SCI AND TECH
News: Prior
infections driving dengue virus evolution in India
What's in the news?
● While
the first infection with any of the four dengue serotypes can prevent
reinfection by the same serotype for a long period.
● The
second infection by a different serotype can have a very high viral load and
cause severe disease.
● This
is because the cross-protection offered
by the first infection acts as a shield against other serotypes only for
two-three years and then begins to drop.
● This
is because while the antibodies are not able to neutralize the virus belonging
to different serotypes, the virus is better able to bind to the antibodies
leading to higher cell infection and thus enhanced severity and viral load.
● This
is called the antibody-dependent
enhancement mediated by cross-reactive antibodies.
Key takeaways:
● In
a nutshell - “While the virus that is identical to the one that caused the
first infection will be neutralized for a long time, viruses that are a bit
look-alike of the serotype that caused the first infection have greater ability
to take advantage of the weakened immune responses and bind to pre-existing
antibodies and cause severe disease than the three other serotypes that did not
cause the first infection”.
Dominant Serotype:
● The
DENV-4-Id lineage is dominant in South
India, and about 50% of infections in South India are due to this India-unique
lineage.
Evolution through Antibody dependent enhancement:
● The
E gene, which is seen across the
dengue virus exterior, plays an important role in binding to the cell
receptors.
● The
substitution rate for the E gene was highest at 44% in genotype I of DENV-4
compared with the whole genome, suggesting high immunological pressure driving
the divergence of the DENV-4 E gene.
● Most
dengue virus evolution happens in the E gene.
● This
suggests that evolution is driven primarily due to interaction with the host
immune system.
Evolution of Dengue virus and vaccine efficiency:
● The
evolution of the viruses across serotypes has implications for vaccine
efficacy. The majority of strains used for developing dengue vaccines are based
on strains isolated between 1964 and 1988.
● Indian
variants of DENV-1 and DENV-4 are distinct from all the vaccines compared to
DENV-2 and DENV-3.
Go back to Basics:
Dengue:
● Dengue
is a mosquito-borne tropical disease
caused by the dengue virus (Genus Flavivirus), transmitted by several
species of female mosquito within the
genus Aedes, principally Aedes aegypti.
● There
are 4 distinct, but closely related, serotypes (separate groups within a
species of microorganisms that all share a similar characteristic) of the virus
that cause dengue (DEN-1, DEN-2, DEN-3
and DEN-4).
● India
recorded 63,280 dengue cases as of September, 2022.
Symptoms: Sudden high
fever, severe headaches, pain behind the eyes, severe bone, joint, and muscle
pain, etc.
Diagnosis and Treatment:
Diagnosis of dengue infection is done with a blood test. There is no specific
medicine to treat dengue infection.
Controlling Dengue Using Bacteria:
● Recently
researchers from the World Mosquito
Program have used mosquitoes infected with Wolbachia bacteria to
successfully control dengue in Indonesia.
Method:
● The
scientists infected some mosquitoes with Wolbachia and then released them in
the city where they bred with local mosquitoes, until nearly all mosquitoes in
the area were carrying Wolbachia bacteria. This is called the Population Replacement Strategy.
● At
the end of 27 months, the researchers found that the incidence of dengue was
77% lower in areas where Wolbachia-infected mosquitoes had been released, as
compared to areas without such deployments.
Dengue Vaccine:
● The
dengue vaccine CYD-TDV or Dengvaxia
was approved by the US Food & Drug Administration in 2019, the first dengue
vaccine to get the regulatory nod in the US.
● Dengvaxia
is basically a live, attenuated dengue
virus which has to be administered in people of ages 9 to 16 who have
laboratory-confirmed previous dengue infection and who live in endemic areas.
● Vaccine
manufacturer Indian Immunologicals Limited (IIL) is developing India's first
Dengue vaccine and has received permission for a Phase-1 trial.
● The
vaccine is being produced in collaboration with the National Institutes of
Health in the US.