Abstract

Since the early 2000s, outbreaks of Highly Pathogenic Avian Influenza (HPAI) both in wild and domestic birds have continued worldwide. In the Republic of Korea, since the first confirmation of HPAI (H5N1) in a breeder chicken farm in December 2003, H5N8 and H5N6 HPAI viruses, as well as H5N1, have been detected for 20 years [1]. According to an investigation about geographical and environmental factors, outbreak timing, and phylogenetic characteristics of the isolated viruses, it was found that the causal virus was introduced to Korea in relation to the migration of birds for wintering [2]. This led the Korean animal health authority to implement a routine surveillance program for avian influenza, which involves sample collection from wild birds (feces or capture), monitoring at slaughterhouses, periodic laboratory tests for breeding farms of chicken and duck, pre-shipment tests (slaughter and eggs), and periodic inspections on live bird markets. Considering that the HPAI is associated with H5 and H7 types of Avian Influenza Virus (AIV), these two types of AIV must be dealt with promptly upon a HPAI outbreak [3]. In the surveillance of wild birds, the H5/H7 AIV can be detected as early as August and September, and usually from October every year. From October 2017 to April 2021, the monthly distribution of positive samples was 0.4% in August, 0.2% in September, 5.6% in October, 14.6% in November, 21.2% in December, 32.8% in January, 17.3% in February, 7.3% in March, and 0.6% in April.