For the first time in the U.S., health officials believe local mosquitoes may have transmitted the Zika virus to humans.

Florida authorities are currently investigating four cases of Zika infection that are believed to have been caused by mosquitoes carrying the virus: two of the four cases are in Miami-Dade County, while the other two were reported in Broward County.

None of the four people involved had traveled to Zika-affected areas, and it’s believed they were infected by local mosquitoes carrying the various. However, sexual transmission has not yet been ruled out.

“We are looking into other modes of transmission. We’re conducting this investigation as we would other mosquito-borne viruses, such as dengue (fever),” the communications director for the Florida Department of Health, told CNN [warning: link contains video that autoplays].

The Centers for Disease Control and Prevention is also helping officials in their investigation.

“Evidence is mounting to suggest local transmission via mosquitoes is going on in South Florida,” Tom Skinner, senior press officer at the Centers for Disease Control and Prevention, told CNN. “These cases fit similar transmission patterns (of) mosquito borne diseases like chikungunya that we’ve seen in South Florida in years past.”

The Florida health department is now giving out Zika-prevention kits in the areas under investigation, our colleagues at Consumer Reports note, with a focus on getting the kits to pregnant women who are at the greatest risk from the virus, which can cause serious birth defects.

Officials are going door-to-door asking people to provide urine samples and other information so they can try to figure out how many people could be infected with Zika. That’s because for most of the other people who contract the virus, they’ll only see mild symptoms or none at all, so they may not even know they’ve got it.

Just in case, the U.S. Food and Drug Administration has asked blood donation centers in the two affected counties to stop collection immediately until officials can screen the blood for Zika, or set up a process that would deactivate it.

Anyone whose traveled to those two counties have also been asked not to donate blood for four weeks after returning from that area, as “a prudent measure to help assure the safety of blood and blood products,” the FDA said.

“Mosquito control has already conducted reduction and prevention activities in the area of investigation,” officials with the Florida Health Department said in a statement. “Residents and visitors are reminded that the best way to protect themselves is to prevent mosquito bites through practicing good drain and cover methods.”

People are also advised to use mosquito repellent.

Florida officials investigating 4 possible non-travel-related Zika cases [CNN]
First Zika Outbreak Confirmed in Florida [Consumer Reports]

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