First report of field cases of Y280-like LPAI H9N2 strains in South Korean poultry farms: pathological findings and genetic characterization

Abstract

H9N2 low-pathogenic avian influenza (LPAI) viruses have long been circulating in the world poultry industry, resulting in substantial economic losses. In addition to bird health consequences, viruses from specific lineages such as G1 and Y280 are also known to have the potential to cause a pandemic within the human population. In South Korea, after introducing inactivated H9N2 vaccines in 2007, there were no field outbreaks of H9N2 LPAI since 2009. However, in June 2020, an H9N2 virus was isolated from an outbreak in a Korean chicken farm. This strain was distinct from the predominant Korean/Y439 lineage and was believed to be part of the Y280-like lineage. Since the first case of this new H9N2 LPAI, nine more cases of field infections in poultry farms were documented through July and December of 2020. Phylogenetic analysis of the haemagglutinin (HA) and neuraminidase genes of these case isolates revealed that all strains were grouped with exotic Y280-like strains that did not previously exist in South Korea and were emerging into a new cluster. Serological assays also confirmed the existence of antibodies to Y280-like viruses in field sera collected from infected birds, and that they had seroconverted. Further analysis of the receptor-binding region in the HA protein also revealed that these isolates harboured a human-like motif that could potentially affect mammals and humans, demonstrating a possible public health risk. This is the first report of field cases caused by Y280-like H9N2 LPAI in the Korean poultry industry. RESEARCH HIGHLIGHTS. Field outbreaks caused by Y280-like H9N2 avian influenza viruses were confirmed.. A human-like motif was found at the HA receptor-binding region of all isolates.

Molecular Detection of Hemagglutinin Gene Fragment of Avian Influenza Virus H9 Subtype Obtained from Poultry Commercial Farm with Prominent Symptom of Decreased Egg Production

“…Pathology macroscopic findings in our study showed various lesions, such as severe tracheitis with tracheal plug, peritonitis, oophoritis with a specific feature of "broccoli," and a white-yellowish spot in the oviduct. This finding is similar to the report of H9N2 infection in layer farms that exhibited tracheitis with caseous plug (Javeen et al 2019;Lai et al 2021). A white to yellowish exudate found in the oviduct and oophoritis with broccoli feature was considered specific lesions that have never been reported in any case the drop of egg production in poultry farms.…”

“…Clinical presentation in the layer commercial farm with decline production sharply in this study is relevant to published data. Lai et al (2021) reported that field cases of LPAI H9N2 strain in layer farms in South Korea showed clinical signs of a respiratory disorder, such as sneezing and gasping, accompanied by egg reduction of over 20%. Several reports confirmed that the AI H9N2 infection did not show apparent clinical symptoms but reduced egg production by 30% (Aamir et al 2007) and up to 80% (El-Houadfi et al 2016).…”

Current situation and control strategies of H9N2 avian influenza in South Korea

“…Although H9N2 AIV is classified as a low pathogenicity virus in poultry, it is causing economic damage to the poultry industry by the decrease in spawning and some mortality rates in commercial chickens. Most chickens infected with H9N2 AIV at farms showed typical signs of influenza, such as respiratory symptoms, egg drop, and mortality (0% to 40%) (summarized in Table 1 ) [ 2 5 61 62 ]. On the other hand, experimental infections in specific-pathogen-free chickens showed no mortality and only mild symptoms, such as depression and decreased feed intake [ 5 19 63 64 65 66 ].…”

Protection of SPF Chickens by H9N2 Y439 and G1 Lineage Vaccine against Homologous and Heterologous Viruses

“…Initially, vaccination reduced the incidence of infection by Y439 lineage H9N2 viruses; indeed, viruses were isolated mainly to unvaccinated live bird markets or from Korean native chickens [ 4 , 22 ]. Although the virus has not been isolated since June 2018, a Y280 lineage H9N2 virus that is distinct from the previously endemic virus has been circulating in Korea since June 2020 [ 23 , 24 ]. In particular, Y439 lineage H9N2 virus is known to replicate preferentially in the gastrointestinal tract, whereas Y280 lineage H9N2 viruses replicate mostly in the respiratory tract and spread rapidly under laboratory-controlled conditions [ 25 ].…”

“…In particular, Y439 lineage H9N2 virus is known to replicate preferentially in the gastrointestinal tract, whereas Y280 lineage H9N2 viruses replicate mostly in the respiratory tract and spread rapidly under laboratory-controlled conditions [ 25 ]. In one study, they showed mortality with 15 birds dying in 1 day and reducing egg production from 10 to 27% in the field [ 24 ]. Hence, a recombinant vaccine candidate against Y280 lineage virus (rgHS314) was developed in Korea [ 26 , 27 ].…”