RIO DE JANEIRO — Brazilian researchers said Thursday they have found Zika in Culex mosquitoes in the northeastern city of Recife in what could prove to be an important discovery. But they cautioned that more study was needed.

Until now, Zika was believed to be carried mainly by the Aedes aegypti mosquito, which is much less numerous, lives in clean water and is more likely to bite during the day. Aedes aegypti thrives in tropical and subtropical climates – it is found in southern U.S. states such as Florida, but is absent in large parts of the United States. The virus is also carried by the Aedes albopictus mosquito, which lives in more rural environments.

Culex mosquitoes are much more widespread. They breed in dirty water and bite at night. Public health officials have feared that Culex mosquitoes could be involved in Zika transmission, something that would necessitate new strategies to combat the disease, which is blamed for an outbreak of the birth defect microcephaly. Brazil has confirmed around 1,700 cases of the birth defect, which causes babies to be born with unusually small heads and can cause cognitive difficulties.

“It means that we have a second species of vector involved in transmission. And with this vector having totally different habits from Aedes aegypti, we will have to create new strategies to combat Culex as well,” said Constancia Ayres, a researcher from the Oswaldo Cruz Foundation, a leading government-led research institute in Recife,.

Researchers collected 5,000 mosquitoes from houses in Recife where suspected Zika transmission had taken place. They found 86 percent of these mosquitoes were Culex.

“Culex is a much more abundant species,” Ayres said in Rio de Janeiro, where she presented the results.

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