The World Health Organization is warning that the mosquito-borne Zika virus, already found in 21 countries, is likely to spread. At least four countries have recommended that women delay getting pregnant due to the potential impact of the virus. “Brazil said the number of babies born with suspected microcephaly — or abnormally small heads — had reached nearly 4,000 since October.”

+ Vox: Zika virus explained in 6 charts and maps.