The growing presence of Zika virus in Brazil has captured international attention in the past week, as one report after another has come in of its apparent link to birth defects in the babies of infected mothers. The news has sparked travel advisories, new guidelines for the care of pregnant women during an outbreak and intense speculation on where the mosquito-borne disease — which had rarely ever been seen in the western hemisphere until last spring — might turn up next.And scientists are starting to ponder whether climate change may play a role in its future spread.