* Mosquito-borne virus linked to birth defects in Brazil
* Brazil's Butantan Institute aims to develop vaccine
* GSK and Sanofi reviewing vaccine possibilities
* More research needed into potential sexual transmission
(Adds comment from GlaxoSmithKline and Sanofi, graphic link)
By Tom Miles and Ben Hirschler
GENEVA/LONDON, Jan 25 (Reuters) - The mosquito-borne Zika
virus, which has been linked to brain damage in thousands of
babies in Brazil, is likely to spread to all countries in the
Americas except for Canada and Chile, the World Health
Organization said on Monday.
Zika transmission has not yet been reported in the
continental United States, although a woman who fell ill with
the virus in Brazil later gave birth to a brain-damaged baby in
Hawaii.
Brazil's Health Ministry said in November that Zika was
linked to a foetal deformation known as microcephaly, in which
infants are born with smaller-than-usual brains.
Brazil has reported 3,893 suspected cases of microcephaly,
the WHO said last Friday, over 30 times more than in any year
since 2010 and equivalent to 1-2 percent of all newborns in the
state of Pernambuco, one of the worst-hit areas.
The Zika outbreak comes hard on the heels of the Ebola
epidemic in West Africa, demonstrating once again how
little-understood diseases can rapidly emerge as global threats.
"We've got no drugs and we've got no vaccines. It's a case
of deja vu because that's exactly what we were saying with
Ebola," said Trudie Lang, a professor of global health at the
University of Oxford. "It's really important to develop a
vaccine as quickly as possible."
Large drugmakers' investment in tropical disease vaccines
with uncertain commercial prospects has so far been patchy,
prompting health experts to call for a new system of incentives
following the Ebola experience.
"We need to have some kind of a plan that makes (companies)
feel there is a sustainable solution and not just a one-shot
deal over and over again," Francis Collins, director of the U.S.
National Institutes of Health, said last week.
The Sao Paulo-based Butantan Institute is currently leading
the research charge on Zika and said last week it planned to
develop a vaccine "in record time", although its director warned
this was still likely to take three to five years.
British drugmaker GlaxoSmithKline GSK.L said on Monday it
was studying the feasibility of using its vaccine technology on
Zika, while France's Sanofi SASY.PA said it was reviewing
possibilities. CONCERNS
The virus was first found in a monkey in the Zika forest
near Lake Victoria, Uganda, in 1947, and has historically
occurred in parts of Africa, Southeast Asia and the Pacific
Islands. But there is little scientific data on it and it is
unclear why it might be causing microcephaly in Brazil.
Laura Rodrigues of the London School of Hygiene and Tropical
Medicine said it was possible the disease could be evolving.
If the epidemic was still going on in August, when Brazil is
due to host the Olympic Games in Rio de Janeiro, then pregnant
women should either stay away or be obsessive about covering up
against mosquito bites, she said.
The WHO advised pregnant women planning to travel to areas
where Zika is circulating to consult a healthcare provider
before travelling and on return.
The clinical symptoms of Zika are usually mild and often
similar to dengue, a fever which is transmitted by the same
Aedes aegypti mosquito, leading to fears that Zika will spread
into all parts of the world where dengue is commonplace.
More than one-third of the world's population lives in areas
at risk of dengue infection, in a band stretching through
Africa, India, Southeast Asia and Latin America.
Zika's rapid spread, to 21 countries and territories in the
Americas since May 2015, is due to the prevalence of Aedes
aegypti and a lack of immunity among the population, the WHO
said in a statement.
RISK TO GIRLS
Like rubella, which also causes mild symptoms but can lead
to birth defects, health experts believe a vaccine is needed to
protect girls before they reach child-bearing age.
Evidence about other transmission routes, apart from
mosquito bites, is limited.
"Zika has been isolated in human semen, and one case of
possible person-to-person sexual transmission has been
described. However, more evidence is needed to confirm whether
sexual contact is a means of Zika transmission," the WHO said.
While a causal link between Zika and microcephaly has not
yet been definitively proven, WHO Director-General Margaret Chan
said the circumstantial evidence was "suggestive and extremely
worrisome".
In addition to finding a vaccine and potential drugs to
fight Zika, some scientists are also planning to take the fight
to the mosquitoes that carry the disease.
Oxitec, the UK subsidiary of U.S. synthetic biology company
Intrexon XON.N , hopes to deploy a self-limiting genetically
modified strain of insects to compete with normal Aedes aegypti.
Oxitec says its proprietary OX513A mosquito succeeded in
reducing wild larvae of the Aedes mosquito by 82 percent in an
area of Brazil where 25 million of the transgenic insects were
released between April and November. Authorities reported a big
drop in dengue cases in the area.
Graphic: Spread of Zika virus http://reut.rs/1JwW4AT
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(Editing by Mark Trevelyan)