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The World Health Organization says that traditional insecticide spraying methods have had no significant impact in slowing dengue, raising significant questions about how officials might stop the spread of the Zika virus, also spread by mosquitoes.
At the conclusion of a Zika research and development meeting on Wednesday, WHO's Marie-Paule Kieny said that "evidence is missing" that the classical ways of fighting dengue have made any substantial dent in reducing cases. She says the same challenge might apply to Zika.
"Everything that was done in the country to control (mosquitoes) apparently didn't work," said Jorge Kalil, director of the Butantan Institute in Sao Paolo, Brazil, who attended the meeting. "The problem right now is it's very difficult to fight the (mosquito), there are billions and billions of insects." He said Brazilian officials may try a more targeted approach calling for more involvement from villages and individuals.
Kieny also noted another possible complication: that other mosquito species beyond Aedes aegypti might also spread Zika. She said that while scientists have observed that other mosquito species can carry the virus, it's unclear if they can actually infect people.
Kieny said experts at the meeting discussed whether innovative methods like using genetically modified mosquitoes might be necessary to stop the outbreak, but noted that "extreme rigor" must be used in evaluating such new tools.
Last month, WHO declared the explosive spread of Zika in the Americas to be a global emergency, due to its link to the spike in the number of babies born with abnormally small heads and the rise in a rare neurological syndrome that can cause paralysis and death.
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So far, Zika has triggered outbreaks in 41 countries, although confirmed cases linking Zika to babies with birth defects have only been seen in Brazil and French Polynesia. Nine countries have reported a spike in cases of Guillain-Barre syndrome, a neurological condition that typically affects people after infections.
Kieny said vaccine development is still at an early stage and that although the most advanced candidates are still months away from preliminary trials, a Zika vaccine is "technologically feasible" based on the development of other vaccines for related diseases like dengue and Japanese encephalitis.