The HEALTH | SEPTEMBER, 2019
14
SENIORS
Fighting
off dengue
with bacteria
Scientists are infecting mosquitoes
to halt the spread of dengue
M
OSQUITOES are among
the deadliest creatures
on earth. Aedes aegypti,
which is recognisable
by the white stripes on
its legs and the lyre pat-
tern on its thorax, can breed in any pool of
stagnant water, which makes it particularly
hard to control. For many years, scientists
have been studying an interesting bacteria
called the wolbachia, looking for ways to use
it to potentially control the mosquitoes that
transmit the dengue virus.
Dr Nazni Wasi Ahmad, Research Offi cer
from the Institute for Medical Research
(IMR) Medical Entomology Unit gives us the
scoop on how Aedes mosquitoes injected with
wolbachia bacteria are about to end the war
against dengue.
What are wolbachia-infected
mosquitoes?
“Wolbachia is a bacterium found naturally
in almost 60 per cent of insects including
fl ies, butterfl ies, grasshoppers, mosquitoes
and other common insects. Th is bacteria
can only live in cells of insects. However, the
Aedes Aegypti mosquito, the main carrier of
dengue fever does not have wolbachia,” she
explains. “Th erefore the wolbachia bacteria
has to be injected into the mosquito’s eggs
using a micro-injection technique. When
these mosquito eggs hatch, all of them will
carry the wolbachia microbe in them. Th ese
infected mosquitoes can then prevent the
spread of dengue virus in the body.”
Wolbachia infected
mosquito strategy
Th ere are two strategies in the game plan; the
fi rst is the population replacement, and the
second is the population suppression.
Dr Nazni explains the
prospect of using
wolbachia as a viable
strategy against
dengue.
Wolbachia is a
bacterium found
naturally in almost
60 per cent of
insects including
fl ies, butterfl ies,
grasshoppers,
mosquitoes and
other common
insects. ”
and reduce the risk of transmission of dengue
fever,” she states.
Wolbachia is a genus
of gram-negative
bacteria that infects
arthropod species,
including a high
proportion of insects,
and also some
nematodes.
How many wolbachia-infected
mosquitoes do we need
to eradicate dengue?
“Th e amount of mosquito released depends
on the area, the population density of the
area, and the number of aedes aegypti mos-
quitoes. For example, in the 0.6km2 area
of AU2 Keramat, as many as 16,000 Aedes
wolbachia-infected mosquitoes are released
weekly.”
Before the release, however, Dr Nazni
informs that spraying of insecticide will be
done to minimize the number of wild Aedes
mosquitoes in the area.
“We also monitor for mosquito repairs
after release. Th e results showed that there
was no signifi cant increase because when
the male Wolbachia-infected mates with the
female in the fi eld, the resulting eggs will not
hatch.”
Locations so far
As of now, the mosquito release studies
have been done in nine high risk dengue
areas around Kelana Jaya, Shah Alam, and
Keramat. Th e areas include Mentari Court,
Kelana Jaya, Flat PKNS Blok ABC, Seksyen 7,
Shah Alam, Jalan Plumbum 103/101 Seksyen
7 Shah Alam, Flat PKNS Blok D, Seksyen 7,
Shah Alam, Jalan Kristal, Seksyen 7, Shah
Alam, Pusat Komersial, Seksyen 7, Shah
Alam, Condo Suria Mas, Kelana Jaya, AU2
Keramat (Landed) and PKNS AU2 Keramat
(Flat). — Th e Health
Population
replacement technique
“In Malaysia, the Ministry of Health practices
the population replacement technique. Th e
objective of this strategy is to replace wild
Aedes mosquitoes in the fi eld that can trans-
mit dengue with the Wolbachia infected edes
mosquito that cannot spread the dengue,”
says Dr Nazni.
For this purpose, male and female Aedes
mosquitoes will be released into the fi eld. Th e
wolbachia-infected female Aedes mosquitoes
will mate with wild male Aedes mosquitoes
in the fi eld and produce wolbachia-infected
eggs. After the eggs hatch and mature, all
adult mosquitoes will have wolbachia in their
body. Mosquitoes with wolbachia can prevent
the spread of dengue virus so, we hope that
the transmission of dengue virus can be
stopped. Do we have to worry about the
wolbachia-infected mosquito?
Populations
suppression technique
“The population suppression strategy
involves the release of only male Aedes
mosquitoes with the wolbachia microbe in
them. When male Aedes mosquitoes mate
with female Aedes mosquitoes in the fi eld,
the resulting eggs will not hatch. Th is, in turn,
will reduce the Aedes population in the fi eld IN efforts to win against dengue, scientist have
inoculated Aedes mosquitoes with wolbachia.
These Wolbachia-fi lled mosquitoes are then
released into the wild for a few weeks so
that they can breed with the wild mosquito
population, ensuring that their offspring also
have wolbachia. Not to worry, wolbachia can
only live in insect cells. The mosquito bites
cannot transmit wolbachia to humans.
Wondering if you can start your own
breeding ground for wolbachia infected
mosquitos? Unfortunately, no. This mosquito
cannot be bred by ordinary people. The
breeders have a Standard Operating
Procedure (SOP) that needs to be strictly
monitored.