Florida health officials said Tuesday they were investigating a possible case of Zika that wasn't carried back by a traveler.
If it's confirmed, it would be the first evidence that Zika has spread to mosquitoes in the continental U.S. All cases up to now have been in people who traveled to Zika-affected regions or their sexual partners.
Small, local outbreaks of Zika virus are fully expected in southern states such as Florida, Louisiana and Texas. These states are home to the Aedes aegypti mosquitoes that most commonly transmit the virus.
"Today the Florida Department of Health announced that it is conducting an investigation into a possible non-travel related case of Zika virus in Miami-Dade County," the health department said in a statement.
"The department is actively conducting an epidemiological investigation, is collaborating with the Centers for Disease Control and will share additional details as they become available."
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The CDC said it will help investigate.
"At this time, state and local officials in Florida are leading the investigation, and CDC is closely coordinating with Florida officials. To date, Florida public health officials have confirmed Zika infection through laboratory testing; upon request, CDC will conduct additional laboratory testing," the agency said in a statement.
Zika can be transmitted by mosquitoes and, less commonly, through sex. The CDC has predicted that a traveler would eventually be bitten by local mosquitoes and infect them with the virus. After about 10 days, an infected mosquito can then transmit the virus to another person.
But in the U.S., it's less common for people to live in the conditions that allow the virus to cause a full epidemic. So the CDC predicts any outbreaks would be limited.
"CDC has been working with state, local, and territorial health officials to prepare for the possibility of locally acquired Zika infection in the United States," the CDC said.
"To date, CDC has provided Florida more than $2 million in Zika-specific funding and about $27 million in emergency preparedness funding that can be used toward Zika response efforts. "
The Florida health department said it would give out Zika prevention kits and repellant in the area under investigation. "Zika kits are intended for pregnant women," it said.
"Mosquito control has already conducted reduction and prevention activities in the area of investigation. Residents and visitors are reminded that the best way to protect themselves is to prevent mosquito bites through practicing good drain and cover methods."
Zika virus is most dangerous to pregnant women, because it can cause severe birth defects in babies if they are infected in the womb. It can cause rare complications such as the paralyzing Guillain-Barre syndrome and very rarely can kill or help kill an already ill patient. An elderly man in Puerto Rico died last spring and Utah reported the death of an elderly patient with Zika last week.
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In Utah, a family caregiver of the patient who died was also infected with Zika and officials there are investigating how it happened, since sexual transmission and mosquitoes can likely be ruled out.
The CDC's reported more than 1,300 cases of Zika in the continental U.S., all linked to travelers. Among them, 346 are or have been pregnant women. Nine babies have been born so far with Zika birth defects and another six were miscarried or aborted.
Health experts caution people in areas where Aedes mosquitoes live to use mosquito repellant, to drain even the smallest reservoirs of standing water in and around homes and to use screens to keep insects out of the house. The mosquitoes that spread Zika bite during the day and prefer to live in and around houses and other structures.
"It was only a matter of time before the right circumstances aligned in Florida," said Dr. Amesha Adalja of the University of Pittsbuch Medical Center's Center for Health Security.