2.1. Sample collection and nucleic acid extraction
The screening for PCV4 was done on 335 samples which were divided into six groups including aborted fetuses (n = 86), suckling (n = 43), weaner (n = 135), grower (n = 23), finisher (n = 20) and sow (n = 28). Except testicles of healthy suckling pigs, which were submitted for herd monitoring of PRRSV, the other pooled internal organs (lungs, spleen, heart, kidneys) of dead pigs/ aborted fetuses were sent for detection of common pathogens of swine. The sampling period was from August- December 2019 and January- August 2020, and covered 36 farms in nine provinces in South Korea. The samples were homogenized, diluted 10-fold with phosphate-buffered saline (PBS 0.1M, pH 7.4), then stored at -70℃. The extraction of total nucleic acid was done using DNA/RNA extraction kit (iNtRON Biotechnology, Inc. Korea). Afterward, extracted nucleic acid samples were again stored at -70℃.