The first known cases of locally transmitted Zika virus in the continental U.S. have been found in Florida, federal health officials said Friday.
Four people appear to have contracted the infection in Miami, according to the Centers for Disease Control and Prevention (CDC).
“All the evidence we’ve seen indicates that this is mosquito-borne transmission that occurred several weeks ago,” said CDC Director Tom Frieden, M.D., M.P.H.
Zika virus is spread primarily through infected Aedes aegypti and Aedes albopictus mosquitoes, although it also can be sexually transmitted.
For months, CDC experts have been monitoring cases spreading throughout Latin America and the Caribbean and preparing for the possibility of local transmission in the states. Their focus has been on pregnant women who can pass on the infection to their fetus, potentially resulting in microcephaly and other brain abnormalities.
Zika virus is spread primarily through infected Aedes aegypti and Aedes albopictus mosquitoes
In U.S. states and Washington, D.C., there already have been 1,658 cases among travelers and their sexual partners, including 433 pregnant women, according to the CDC. When an infected person is bitten by a mosquito, the insect then can infect another person.
While the CDC has advised pregnant women not to travel to countries with local transmission, it is not recommending such restrictions in Florida at this time.
“If we were to see continuing spread in this area or somewhere else or explosive spread, we would absolutely issue travel guidance,” Dr. Frieden said. “That’s not the situation we’re in today, but we will reassess that every single day.”
However, he said people around the country, especially pregnant women, should take steps to avoid mosquito bites while in areas with Aedes mosquitoes. In addition, the Food and Drug Administration has called for blood donation centers in Miami-Dade and Broward counties in Florida to stop collecting blood until they implement testing.
For the 20% of those infected who display symptoms, the illness is mild and may include fever, rash, joint pain and conjunctivitis. Dr. Frieden said he would not be surprised to see additional cases and possibly clusters.
“We believe that widespread transmission in the continental U.S. is unlikely, but it’s not impossible and that’s why we’re aggressively keeping our guard up and investigating every possible incident that may represent widespread transmission,” he said.
The virus is a nationally notifiable disease and should be reported to local, state or territorial health departments to facilitate testing. The CDC also is asking health care providers to contribute data to its Zika pregnancy registry that will follow children exposed to Zika for up to 1 year of age.
President Barack Obama has requested $1.9 billion from Congress to combat the virus, but lawmakers have not reached an agreement on how much funding to provide. In the meantime, the CDC is borrowing $589 million, largely from Ebola funds.
“We are doing the best we can with the resources we have available to us …” Dr. Frieden said. “If we had more resources, we would be able to mount a more robust response.”