In the six months since Zika was declared a global public health emergency, the virus has continued its unrelenting march across the Americas, spreading to more than 40 countries and territories and stirring panic among pregnant women and their families.
On Friday, the Centers for Disease Control and Prevention said four patients in Florida were probably infected with Zika by local Aedes species mosquitoes — the first evidence of mosquito-borne transmission in the continental United States. The virus, which can also be spread sexually, was already circulating in the U.S. territories of Puerto Rico, American Samoa and the U.S. Virgin Islands.
Zika was long thought to be relatively harmless. The symptoms, which can include fever and rashes, are generally mild, and most of those infected do not feel ill.
The World Health Organization sounded the alarm Feb. 1 after Brazil reported a surge in the number of babies born with microcephaly — an abnormally small head — and brain damage that appeared to be linked to the virus. The WHO and CDC have since confirmed that Zika infections in pregnant women can cause serious harm to their fetuses.
The virus is not generally considered dangerous to people who aren’t pregnant. But in rare cases, it has been linked to Guillain-Barre syndrome, an immune system disorder that can cause temporary paralysis.
The discoveries, WHO Director-General Dr. Margaret Chan said in February, changed the risk profile of Zika from a mild threat to one of “alarming proportions.”
Researchers now say that the epidemic may already have peaked in Latin America and could be largely over in three years. Scientific teams are studying several promising vaccine candidates.
However, the release of a vaccine that is safe for humans could still be years away. Without such protection, CDC Director Dr. Thomas Frieden warned in June, the virus remains “an emergency that we need to address.”