Surveillance of avian influenza viruses from 2009 to 2013 in South Korea

Abstract

Avian influenza viruses (AIVs) are carried by wild migratory waterfowl across migratory flyways. To determine the strains of circulating AIVs that may pose a risk to poultry and humans, regular surveillance studies must be performed. Here, we report the surveillance of circulating AIVs in South Korea during the winter seasons of 2009-2013. A total of 126 AIVs were isolated from 7942 fecal samples from wild migratory birds, with a total isolation rate of 1.59%. H1‒H7 and H9‒H11 hemagglutinin (HA) subtypes, and N1‒N3, N5, and N7‒N9 neuraminidase (NA) subtypes were successfully isolated, with H6 and N2 as the most predominant HA and NA subtypes, respectively. Sequence identity search showed that the HA and NA genes of the isolates were highly similar to those of low-pathogenicity influenza strains from the East Asian-Australasian flyway. No match was found for the HA genes of high-pathogenicity influenza strains. Thus, the AIV strains circulating in wild migratory birds from 2009 to 2013 in South Korea likely had low pathogenicity. Continuous surveillance studies such as this one must be performed to identify potential precursors of influenza viruses that may threaten animal and human health.

Figure 1

Sampling sites and hemagglutinin (HA) and neuraminidase (NA) subtypes of isolated avian influenza viruses from the fecal matter of wild migratory birds from 2009–2013. (a) Sampling sites (triangles) from 2009–2013, and representative clusters of highly pathogenic avian influenza outbreaks in poultry in South Korea from 2008–2014 (circles). Frequencies of isolates (out of 126 total isolates) per sampling site are shown in the pie chart. All (b) HA and (c) NA subtypes were identified through reverse transcription polymerase chain reaction using universal primers.

Figure 2

Overall frequency of hemagglutinin (HA) and neuraminidase (NA) subtypes of avian influenza viruses (AIVs) isolated from the fecal matter of wild migratory birds in Korea (2009–2013). The frequencies of (a) HA subtypes, (b) NA subtypes, and (c) HA and NA combinations of AIV isolates were calculated relative to the total number of isolates (n = 126). NX: unknown NA subtypes.

Figure 3

Phylogenetic analyses of representative H6- and N2-subtype avian influenza fecal isolates in South Korea in 2009–2013. The assembled (a) H6-subtype hemagglutinin and (b) N2-subtype neuraminidase coding sequences of representative isolates (blue, underlined) were compared to different isolates from various locations. Wildfowl migratory flyways that cover these locations are indicated. Bootstrap values ≥ 600 are shown. BSMF Black Sea-Mediterranean flyway, EAAF East Asian-Australasian flyway. Red diamond: the Republic of Georgia is at the intersection of the BSMF, Central Asian, and East Africa-West Asian flyways.