Yesterday we wrote about the prospect of viruses like Ebola spreading around the world via air travel. Today brings us more proof of just how swiftly this can happen. A resident of Saudi Arabia who visited Greece for Easter brought the MERS virus into the country and is currently in intensive care. So far, however, no one who came into contact with him has tested positive for the disease.Seventy-three people, including the man’s wife, the passengers on the plane, and a taxi driver were exposed to the virus. If just one of them had been infected and remained at large for the rest of the day, hundreds of other people could have been exposed. Just think about how many people visit a modern airport over the span of a few hours.Airports are the doorways to every modern nation and thus the global entry points for disease. It’s chilling to see a virus that originated in the Middle East travel so easily to three countries thousands of miles away from the region: Malaysia and the Philippines as of last week, and now Greece. If you weren’t worried about the transmission of diseases across continents before, you should be now.