Zika virus, a 40-nm sized capsule of about a dozen genes, is on the move. The recent flare-up of cases in Brazil has diffused across borders into Colombia and Venezuela, Mexico and Puerto Rico. And while the full extent of the virus’ spread is difficult to predict, most experts agree on one thing: it will soon gain a foothold in the United States. The South, where the requisite carrier mosquitos (two species of the Aedes genus) live, is particularly susceptible, but if the virus can evol