A genetic mutation in the chikungunya virus may have led to a
massive outbreak of the deadly tropical disease on an island in the
Indian Ocean in 2005 and 2006,according to the findings of research
published Thursday.
The mutation made it easier for the virus to reproduce inside
the mosquitoes that transmit it to humans, said the findings
published in the online journal of PLoS.
Chikungunya kills about one in every 1,000 infected people. The
outbreak at La Reunion, a French island 700 km east of Madagascar,
infected at least a third of the 800,000 inhabitants there.
From analyzing various versions of viruses isolated from
patients, researchers knew that chikungunya had undergone a
mutation early in the epidemic. They suspected that the change had
facilitated the spread, but this was mostly speculation. Now they
have the proof.
The virus was spread mainly by the Asian tiger mosquito, A.
albopictus. Scientists at the Pasteur Institute in Paris bred
populations of the A. albopictus mosquitoes from La Reunion and
nearby Mayotte and fed them a blood meal spiked with mutated and
non-mutated versions of the virus.
The scientists then ground up the insect bodies at different
time intervals after feeding and measured the amount of virus
inside.
In mosquitoes fed with the mutated version, the virus occurred
in quantities almost 100 times higher than in those without.
This mutated virus was also better able to pass the wall of a
mosquito's midgut and make its way to the salivary glands, from
where it could pass to a new victim with the insect's next
bite.
Apparently, the mutation made the virus a much better fit for La
Reunion's Asian tiger mosquito population and thus made the
epidemic soar.
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(Xinhua News Agency November 16, 2007)