Australasian Science
Brief: UNIQ_CORP
Page 1 of 2
July, 2009
Page: 30
Section: General News
Region: National Circulation: 9,000
Type: Magazines Science / Technology
Size: 674.23 sq.cms.
Frequency: Monthly
A Bacterial Cure
for Viral Infection
BY LAUREN HEDGES and KARYN JOHNSON
Infection with a bacteria protects insects from highly pathogenic
viruses, opening the way to strategies to control viruses spread
by insects to animals and plants.
Ever had the flu % Then you know
what it's like to be infected with
produce more virus than others. The
aturr- and light-controlled incubator.
Each day the number of flies that have
biological mechanisms that determine
a virus. Many human diseases are
died is recorded. This data is used to
susceptibility in insects are not well
caused by a viral infection, and scientists
analyse how quickly a virus causes death.
understood.
around the world are working to produce
Normally flies injected with
effective vaccines and treatments for a
range of viruses.
Some viruses that cause disease in
humans are transmitted from one person
We set out to understand the biolog-
ical mechanisms used in insects to reduce
susceptibility to virus infection. To
examine this question we looked at virus
infection in the vinegar fly, Dmsophila
(or animal) to another by insects,
melanogaster.
including ticks and mosquitoes. SimiThe vinegar fly is a common insect;
larly, aphids and some other insects
transmit viruses between plants. For these
you have probably seen it hanging around
Drosophila C virus survive less than
6 days. In our experiments we identified
a fly line that was much less susceptible to
virus infection than normal flies. These
resistant flies survived for up to 14 days.
That is more than twice as long!
The delay in fly death corresponded
with a delay in virus accunu lation. We
found this by collecting flies 2 days and
7 days after injection of Drosophila C
your fruit bowl. This insect is also a
viruses, in addition to treatments like popular laboratory animal. In the past
vaccines that protect individuals from 100 years the vinegar fly has been exteninfection, controlling the spread of disease sively used in research to study many virus and measuring the number of copies
could also be achieved by interfering with different biological processes. As a conse- of the virus. Two days after injection
the viral cycle within the insect.
quence the scientific community has a there was 1700 times more virus in the
The virus first encounters the insect range of different "lines" of the fly - these susceptible flies compared with the
when the latter feeds on an infected host. are genetically different families of vinegar amount originally injected.
The most common point of viral entry flies.
In stark contrast, the amount of virus
into the body of the insect is via the gut.
in
the
resistant flies had only increased
We use the vinegar fly to study
The virus then infects the cells of the antiviral responses. Flies are injected with 10-fold. That is, the susceptible flies
insect, where it produces more copies of
contained more than 100 times more
virus and their survival is monitored.
itself in a process called virus replication.
The flies are first anaesthetised using virus than the resistant flies.
The new virus then moves through the
The amount of virus in the resistant
carbon dioxide. While they are immoinsect to the mouth-parts and are transflies
did increase with time. By 7 days
bilised, virus is injected into the abdomen
mitted in the saliva when the insect feeds
of each fly using extremely fine glass after injection, virus produced in the
on an uninfected host.
needles. This is done under a microscope. resistant flies was 1400 times more than
Not all insects will become infected
The injected flies are then put into plastic the amount injected. This showed that
when exposed to a virus, and some among
vials containing fly food. Once the flies there was a significant delay in the rate
the insects that do become infected will
wake up the vials are placed in a temper-
e\nerience crrnno,'r cvmnrnnic arvJ
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Australasian Science
Brief: UNIQ_CORP
Page 2 of 2
July, 2009
Page: 30
Section: General News
Region: National Circulation: 9,000
Type: Magazines Science / Technology
Size: 674.23 sq.cms.
Frequency: Monthly
of virus accumulation in the resistant flies.
So what made these flies less susceptible to Drosophila C virus? We found
that they were infected with a bacterium
called lf'olbachia. Flies that were cured
from iolbachia infection were just as
susceptible to Drosophila C virus as
normal flies.
This finding was very unexpected! It
was the first time a bacteria had been
shown to protect a host from virus infection.
There are many different types of
viruses. To determine whether Wolbachia
infection also protects flies from other
viruses we challenged flies with cricket
paralysis virus and Flock House virus. For
both viruses the flies without Wolbachia
died within a week while the flies with
Wolbachia survived much longer. This
showed that Wolbachia provides flies with
a robust antiviral protection against a
This antiviral effect is particularly
interesting as JI'olbachia is very common
in insects. If this type of interaction is
widespread there could be significant
biological implications.
First, a reduction in insect death due
to viral infection could change the way
viruses are maintained in insect popula-
tions. Second, the large decrease in the
amount of virus produced in an insect
may significantly reduce the chance of
the virus being transmitted to another
host.
II'olbachia is maternally inherited.
That is, if a female insect is infected it
passes the bacteria in the egg to the next
generation. This means that if a mother
that the virus will be transmitted to an
uninfected fly.
For insects that transmit viruses
between plants or animals, we would also
predict that a decrease in viral replication
would lead to a decrease in transmission
of the virus. That is, Wolbachia-infected
insects may be less able to spread viruses
that cause disease in crop plants, humans
and animals, so this may be a strategy that
can be used to control the spread of
viruses that are transmitted to humans
by mosquitoes, like dengue virus or Ross
River virus.
How does ff'olbachia reduce viral
replication and virus induced death in
insects? We are working to understand
is protected from viruses then her
these biological processes. Once we under-
offspring will also be protected. This is a
big advantage for the insect!
Viral replication in flies infected with
stand them we may be able to use them to
I I 'olb,zchiaz is much slower. A reduction in
help control insect-transmitted diseases.
Lauren Hedges is a postgraduate student supervised by Dr Karyn
Johnson in The University of Queensland's School of Biological
Sciences.
the amount of virus reduces the chance
range of different viruses.
A fl y on the end of a glass needle used to inject virus.
vnoo. s.<wn. code, m<w.N: ao«noe
Electron micrograph of a virus.
Photo laureo Hedg.
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