SEOUL, South Korea (AP) — The U.S. and South Korean militaries, used to being on guard for threats from North Korea, face a new and formidable enemy that could hurt battle readiness: a virus spreading around the world that has infected more than 1,200 people in South Korea. As the new coronavirus has begun to sweep through South Korea, soldiers stationed in close quarters on bases throughout the country are at particular risk. Already 20 South Korean soldiers and one American have tested positive. In response the allies are taking aggressive measures to guard against a viral outbreak and are even considering curtailing a key joint military exercise, something experts say is inevitable because if the virus were to spread through the ranks it could significantly weaken their ability fight if necessary.