Florida officials have found mosquitoes in Miami Beach infected with Zika, the first time the virus has been detected in mosquitoes in the continental United States.
Officials had already announced that Zika is circulating in a portion of Miami Beach and a neighborhood in Miami after deducing that some Zika cases could only have been acquired from local mosquitoes. But discovering Zika-positive mosquitoes amounts to what authorities have described as a smoking gun that local Zika transmission is indeed occurring.
So far, federal health officials have identified the two zones in Miami Beach and Miami as the only spots of active Zika transmission in the United States and have recommended pregnant woman avoid traveling to those areas if possible.
As of Wednesday, Florida had seen 47 local Zika cases. It has had 569 cases related to people traveling to other regions where Zika is spreading, including 80 involving pregnant women.
The three Zika-positive mosquito samples came from a small area in Miami Beach, the state’s Department of Agriculture and Consumer Services announced Thursday. A mosquito sample typically consists of material from more than a dozen individual mosquitoes.
Officials ramped up their trapping and testing of mosquitoes after local spread was identified, and the department said that 95 additional mosquito samples from the area have tested negative for Zika since infected mosquitoes were identified.
Since May, the state has tested more than 40,000 mosquitoes, the department said.
The Zika virus, which has spread rapidly through much of Latin America and the Caribbean, is transmitted mainly by mosquitoes, but can also be passed through sex. It typically causes mild symptoms or none at all, but it can cause severe birth defects in fetuses when it infects pregnant women.
Since the discovery of local Zika spread in Miami-Dade County, officials have expanded their mosquito control efforts, with particular focus in the two areas where transmission is active. One challenge in fighting mosquitoes in Miami Beach is the city’s famous high rises, which create wind tunnels and prevent planes from flying low enough to dispense insecticide effectively.