* Mosquito-borne
virus
linked to birth defects in Brazil
* Brazil's Butantan Institute aims to develop vaccine
* No cases yet reported in continental United States
* More research needed into possible sexual transmission
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
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," Trudie Lang, a professor of global health at the University of Oxford, said on Monday. "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.
RIO 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, 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. (Editing by Mark Trevelyan)