Singapore's Zika cases send warning signal to Asia.

In just one week, Zika cases in Singapore have gone from zero to 242, raising concerns about a potential rapid surge in cases across Asia. A recent study estimates that roughly 2.6 billion people in the region and Africa could be at risk of contracting the virus, which has been linked to the neurological disorder microcephaly in unborn babies. It's not yet clear why Zika has spread so suddenly in Singapore. Many of the cases are thought to be locally-transmitted by the Aedes aegypti mosquito. On Saturday, Singapore's Ministry of Health said analysis of two cases found they had likely evolved from a strain of Zika that was already circulating in Southeast Asia. Malaysia confirmed its first case of Zika infection in a 58-year-old woman -- who had visited her daughter in Singapore -- on September 1. The country reported its first locally-transmitted case on September 3, with authorities expecting more to come. With 5.7 million-strong populace packed mostly in dense urban areas, Singapore doesn't immediately strike you as the kind of place that would suffer long from a Zika outbreak. But it's the city state's high population density and humid climes that offer the perfect breeding ground for the Aedes aegypti. And these are traits shared across many cities in the region. "In Asia, you have megacities with populations between five to 10 million people. The Aedes aegypti thrives in these densely-packed urban environments," Eng Eong Ooi, the deputy director of the Emerging Infectious Disease program at Duke-NUS Medical School in Singapore, told CNN. Where there high populations of people and mosquitoes, it's a good recipe for both dengue and Zika to spread,continue