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Mosquito trials raise hopes of defeating dengue
NHA TRANG, Vietnam, Sept 10, 2019 (BSS/AFP) – Hundreds dead in the
Philippines; a threefold increase of cases in Vietnam; hospitals overrun in
Malaysia, Myanmar and Cambodia — dengue is ravaging Southeast Asia this year
due in part to rising temperatures and low immunity to new strains.
But one group of scientists is rolling out trials to breed dengue-
resistant bugs in a bid to tackle one of the world’s leading mosquito-borne
illnesses, raising hopes the untreatable disease can finally be beaten.
The World Mosquito Program (WMP) has pioneered a method where male and
female Aedes Aegypti mosquitoes are infected with the disease-resistant
bacteria called Wolbachia before being released into the wild.
In a matter of weeks, baby mosquitoes are born carrying Wolbachia, which
acts as a disease buffer for the bugs — making it harder for them to pass on
not only dengue, but Zika, chikungunya and yellow fever.
First trialled in northern Australia, it’s been tested in nine countries
around the globe, including in Vietnam where early results are promising.
“We have seen a remarkable reduction of dengue cases after the release,”
explained Nguyen Binh Nguyen, project coordinator for WMP in Nha Trang.
His team set free around half a million Wolbachia-infected mosquitoes last
year in Vinh Luong, a crowded dengue-prone district in southern Vietnam.
Since the trials, dengue cases are down 86 percent in Vinh Luong compared
to nearby resort town Nha Trang.
That’s a major relief for Cong Thi Thu, an accountant who along with her
two children suffered an intense bout of dengue in 2016, flooring the family
for weeks.
She worries less after the trials but still makes her kids sleep under
nets and no longer leaves stagnant water to collect in the pots around her
garden, which offer ideal breeding grounds for mosquitoes.
“I feel at ease now, 70 to 80 percent safe, but I still have to be
careful,” Thu said from her leafy compound.
– No immunity –
Today, mosquitoes still buzz about in the open-air shops, cafes and homes
of Vinh Luong, but the majority in the test areas now carry Wolbachia
compared to none before the trials, WMP said.
Convincing wary residents like Thu, along with health officials and ethics
boards, that the mosquitoes won’t make them sick was not an easy task.
Residents have long suscribed to the official motto “no mosquitoes, no
larvae, no dengue” to avoid the virus, dubbed “breakbone fever” because of
its severe flu-like symptoms.
MORE/SSS/1635 hrs
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Dengue is passed along to humans by infected mosquitoes, which thrive in
crowded, hot and humid neighbourhoods like Thu’s.
Cases have surged not only in Vietnam this year but across Southeast Asia,
with around 670,000 infected and more than 1,800 people dead in the region,
according to an AFP tally of national and World Health Organization data.
Experts say it’s the worst outbreak in years.
Warmer weather is one factor — temperatures in July 2019 were the hottest
ever recorded globally, and mosquitoes love hot weather — coupled with the
introduction of new dengue strains that have spread among populations with no
immunity.
Long-term trends are also at play: breakneck urbanisation in Asian
megacities, a massive increase in international travel and trade and the
cyclical nature of outbreaks.
“That creates the perfect ingredients for the dengue epidemic to happen,”
Rachel Lowe, assistant professor at the London School of Hygiene & Tropical
Medicine, told AFP.
Even the widespread use of plastics has contributed — as things like
garden pots and takeout containers collect water they create perfect breeding
pools for mosquitoes.
– Re-invasion –
Wolbachia was first discovered by scientists in the 1920s in mosquitoes
living in the drainage system beneath the Harvard University School of Public
Health.
Found in 60 percent of all insect species — including dragonflies, fruit
flies and moths — the bacteria was mostly ignored until the 1970s when
researchers discovered it could be used to prevent the spread of disease by
bugs.
Over the years scientists have conducted anti-dengue experiments with
Wolbachia-laden mosquitoes with varied success, but now WMP hopes its
approach will stick.
It is one of the only organisations in the world seeking to repopulate
colonies with Wolbachia-infected mosquitos to fight dengue, estimated to
spread to as many as 100 million people globally every year.
Other groups, including in Singapore and Malaysia, are using Wolbachia but
only in male mosquitoes who render female eggs infertile — a method that
aims to suppress the mosquito population, which rarely lasts.
Many countries are also fogging neighbourhoods with insecticides —
effective in the short term, though the mosquitoes often come back in just a
few days, or develop resistance to the chemical killers.
“No one has been able to get long-lasting suppression because the
mosquitoes just keep re-invading,” said WMP director Scott O’Neill.
Results from WMP’s Wolbachia trials in northern Australia and on the
Vietnamese island Tri Nguyen have been positive — local dengue transmissions
are almost non-existent — and outcomes from trials in Indonesia are expected
in the next year.
But experts say more long-term, and large-scale, studies are needed to see
if the approach really works.
Dr Raman Velayudhan, coordinator of WHO’s global control programme on
dengue, said: “Our bottom line is to make sure that it leads to the reduction
of the disease.”
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