The first cases of Zika virus transmitted in the continental United States by mosquitoes have been recorded in Florida, the south-eastern state's governor said.
Four people, three men and a woman, were infected with the disease in Miami, Governor Rick Scott said.
Previous reported cases of Zika virus in the United States involved people who had been infected while traveling or via sexual transmission, and the latest cases mark a shift for US health officials who have warned that the disease could become more widespread if infected mosquitoes reached the United States.
“We anticipate that there may be additional cases of ‘homegrown’ Zika in the coming weeks," said doctor Lyle Petersen, who heads the Zika response team at the US Centres for Disease Control and Prevention (CDC). "Our top priority is to protect pregnant women from the potentially devastating harm caused by Zika.”
The virus is spread primarily via mosquitoes, and Latin America has faced an outbreak in recent months. The virus generally causes mild symptoms in adults, but can cause severe birth defects in the children of pregnant women who become infected with the virus.
Florida health officials stressed the outbreak seemed to be confined to a small area of just a few city blocks, and officials were going door-to-door to conduct testing.
There have been 1,658 cases of Zika in the United States, but so far none had been the result of local transmission by mosquitoes, the CDC said.
The virus is far more widespread in the US Caribbean territory of Puerto Rico, where the CDC said Friday that more than 5,500 people have tested positive for the virus, including 672 pregnant women.
An outbreak of the virus that began last year has since spread throughout Latin America and the Caribbean. The US Congressional Research Service estimated 4 million people in the western hemisphere could be at risk of infection in 2016.
In Brazil alone 1.5 million people have been infected with the virus, which can cause severe neurological defects in babies born to mothers infected with the virus.