Spatiotemporal Dynamics of Highly Pathogenic Avian Influenza Subtype H5N8 in Poultry Farms, South Korea

Abstract

Highly pathogenic avian influenza (HPAI), a zoonotic disease, is a major threat to humans and poultry health worldwide. In January 2014, HPAI virus subtype H5N8 first infected poultry farms in South Korea, and 393 outbreaks, overall, were reported with enormous economic damage in the poultry industry. We analyzed the spatiotemporal distribution of HPAI H5N8 outbreaks in poultry farms using the global and local spatiotemporal interaction analyses in the first (January to July 2014) and second (September 2014 to June 2015) outbreak waves. The space-time K-function analyses revealed significant interactions within three days and in an over-40 km space-time window between the two study periods. The excess risk attributable value (D₀) was maintained despite the distance in the case of HPAI H5N8 in South Korea. Eleven spatiotemporal clusters were identified, and the results showed that the HPAI introduction was from the southwestern region, and spread to the middle region, in South Korea. This spatiotemporal interaction indicates that the HPAI epidemic in South Korea was mostly characterized by short period transmission, regardless of the distance. This finding supports strict control strategies such as preemptive depopulation, and poultry movement tracking. Further studies are needed to understand HPAI disease transmission patterns.

Keywords: H5N8 subtype; South Korea; Spatiotemporal analysis; avian influenza.

Figure 1

Location of highly pathogenic avian influenza case farms in the first and second waves. Red round dots are the outbreaks in poultry farms during the first wave from 14 January 2014 to 29 July 2014. Green triangles are the outbreaks in poultry farms in the second wave from 23 September 2014 to 24 June 2015. Province abbreviations: CB: Chungbuk, CN: Chungnam, GB: Gyeongbuk, GG: Gyeonggi, GN: Gyeongnam, GW: Gangwon, JB: Jeonbuk, JN: Jeonnam.

Figure 2

Epidemic curve of HPAI H5N8 from 2014–2015: (a) the epidemic curve of the first wave of HPAI H5N8 is from January 2014 to August 2014 in South Korea; (b) the epidemic curve of the second wave of HPAI H5N8 is from September 2014 to July 2015 in South Korea. HPAI, highly pathogenic avian influenza.

Figure 3

Excess risk attributable to the space–time interaction (D₀) as a function of space and time. (a) Excess risk attributable to the space–time interaction of the first wave of HPAI H5N8 from 14 January 2014 to 29 July 2014. (b) Excess risk attributable to space–time interaction of the second wave of HPAI H5N8 from 23 September 2014 to 24 June 2015. The red-shaded area shows the space–time interaction for which the observed number of cases was higher than twice the expected number, which assumes no space–time interaction (D₀ > 1). HPAI, highly pathogenic avian influenza.

Figure 4

Spatiotemporal cluster of poultry farms during the first wave of HPAI H5N8 outbreaks in Korea. The left map shows whole area of South Korea; (A) spatiotemporal cluster of the first wave of HPAI H5N8 in the midwest region; (B) spatiotemporal cluster of the first wave of HPAI H5N8 in the southwest region. Red round dots are the outbreaks in poultry farms at the first wave from 14 January 2014 to 29 July 2014. The locations of the clusters are indicated by black circles and clusters name is shown by black arrow. Province abbreviations: CB: Chungbuk, CN: Chungnam, GB: Gyeongbuk, GG: Gyeonggi, GN: Gyeongnam, GW: Gangwon, JB: Jeonbuk, JN: Jeonnam.

Figure 5

Spatiotemporal cluster of poultry farms during the second wave of HPAI H5N8 outbreaks in Korea. The left map shows whole area of South Korea; (A) spatiotemporal cluster of the second wave of HPAI H5N8 in the midwest region; (B) spatiotemporal cluster of the second wave of HPAI H5N8 in the southwest region. Green triangles are the outbreaks in poultry farms at the second wave from 23 September 2014 to 24 June 2015. The locations of the clusters are indicated by black circles and clusters name is shown by black arrow. Province abbreviations: CB: Chungbuk, CN: Chungnam, GB: Gyeongbuk, GG: Gyeonggi, GN: Gyeongnam, GW: Gangwon, JB: Jeonbuk, JN: Jeonnam.