1 Department of Respiratory Infections, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan; School of Tropical Medicine and Global Health, Nagasaki University, Nagasaki 852-8523, Japan. Electronic address: b-gopal@nagasaki-u.ac.jp.
2 Department of Respiratory Infections, Institute of Tropical Medicine, Nagasaki University, Nagasaki 852-8523, Japan.