We've seen it coming for months. Zika has been moving with hurricane intensity throughout South America and the Caribbean, appearing for the first time in 42 countries in the Western Hemisphere in less than two years. Originally thought a mild infection, Zika's unanticipated ability to cause serious fetal abnormalities startled scientists and health officials into taking the virus much more seriously. Experts have been warning for months that the U.S. mainland was vulnerable, too, especially southern states that still harbor Aedes aegypti, the principal mosquito species involved in Zika transmission. So it should come as no surprise that last Friday, the Centers for Disease Control and the Florida Department of Health confirmed what we've all been expecting: four locally transmitted cases of Zika in Miami-Dade and neighboring Broward counties, all apparently acquired in the same part of Miami. Ten more cases were confirmed on Monday, and it is very likely more will come to light over the coming weeks.
The Aedes aegypti mosquito is notorious for efficiently transmitting deadly yellow fever and dengue, a ubiquitous tropical disease, as well as Zika. A number of U.S. states, especially in the Gulf, have their own sizable populations of Aedes aegypti. Once the local mosquitoes pick up one of these viruses by biting an infected person, they can transmit them as efficiently as their tropical cousins. We know this historically from the rough parallel of dengue, carried by the same mosquito species, which has caused outbreaks in Puerto Rico (now also suffering from Zika since December 2015), Florida, Texas and Arizona.
