1. Department of Occupational Health, College of Bio-Medical Sciences, Daegu Catholic University, Gyeongsan 38430, Korea.
2. Technology Services Division, National Institute of Animal Science, Wanju 55365, Korea.
3. Dodram Pig Farmer's Cooperative, Veterinary Service Center, Daejeon 35352, Korea.
4. Department of Preventive Medicine, College of Medicine, The Catholic University of Korea, Seoul 06591, Korea.