Elucidating the Local Transmission Dynamics of Highly Pathogenic Avian Influenza H5N6 in the Republic of Korea by Integrating Phylogenetic Information

Abstract

Highly pathogenic avian influenza (HPAI) virus is one of the most virulent and infectious pathogens of poultry. As a response to HPAI epidemics, veterinary authorities implement preemptive depopulation as a controlling strategy. However, mass culling within a uniform radius of the infection site can result in unnecessary depopulation. Therefore, it is useful to quantify the transmission distance from infected premises (IPs) before determining the optimal area for preemptive depopulation. Accordingly, we analyzed the transmission risk within spatiotemporal clusters of IPs using transmission kernel estimates derived from phylogenetic clustering information on 311 HPAI H5N6 IPs identified during the 2016–2017 epidemic, Republic of Korea. Subsequently, we explored the impact of varying the culling radius on the local transmission of HPAI given the transmission risk estimates. The domestic duck farm density was positively associated with higher transmissibility. Ring culling over a radius of 3 km may be effective for areas with high dense duck holdings, but this approach does not appear to significantly reduce the risk for local transmission in areas with chicken farms. This study provides the first estimation of the local transmission dynamics of HPAI in the Republic of Korea as well as insight into determining an effective ring culling radius.

Analyzing Spatial Dependency of the 2016–2017 Korean HPAI Outbreak to Determine the Effective Culling Radius

“…Two recent studies have estimated the effective culling radius based upon the 2016–2017 HPAI outbreak in Korea [ 21 , 23 ]. In both Yoo et al [ 21 ] and Lee et al [ 23 ], the analyses were focused upon the same general time period of the 2016–2017 outbreak and were constrained to Chungbuk in Korea containing higher densities of duck farms. Thus, conclusions from these previous studies may be particular to that region and time period during the 2016–2017 HPAI outbreak.…”

“…Lee et al [ 23 ] estimated an effective culling radius of 2.24 km, when not considering spatial heterogeneity, and 2.65 km when spatial heterogeneity, represented by the local reproductive numbers of the virus, was considered. Yoo et al [ 21 ] simulated the risk for the local transmission of HPAI based upon the heterogeneity of the different clusters as determined by the genotype of the viruses and, although not conclusive, suggested that culling radii between 2–3 km are more appropriate, but only in areas with high densities of duck farms.…”

“…Not only is livestock culled from the original farm infected by HPAI, but also from surrounding farms up to a 3 km radius. However, the culling radius has not been consistent, and different culling radii have been used as control measures [ 21 ]. Before 2017, the culling radius was 500 m. In the seventh HPAI outbreak of 2016–2017, the radius was extended to 3 km and led to the culling of 37.8 million poultry from 946 poultry farms.…”

“…Due to such large-scale economic damages and the different culling radii implemented, both poultry farms as well as the government have raised concerns about providing a more scientific rationale for the most effective culling range. However, little research has investigated the proper culling range to contain HPAI outbreaks in Korea until recently [ 21 , 23 ].…”

Spatial Distribution Pattern and Influencing Factors of Sports Tourism Resources in China

“…This formula has been tested many times, and the data selection search bandwidth is 333.6 km to more intuitively reflect the spatial distribution of sports tourism resources. Yoo et al [14] and Allen et al [15] made use of kernel density in order to determine the center position of a specific element. The density is the highest at the center position, and it decays with distance.…”