North Korean leader Kim Jong Un has sent a letter expressing hope for South Korea to overcome a coronavirus outbreak, President Moon Jae-in's office said on Thursday, as the South battles the biggest epidemic of the disease outside China.The two sides' exchanges have ground nearly to a halt after the North closed borders and temporarily shut a joint liaison office in a border city to avert an outbreak, while the South added 438 infections on Thursday to swell its tally to 5,766.