- The National Agriculture and Food Research Organization(NARO) has conducted genetic analysis on the high pathogenicity avian influenza viruses(HPAIV) identified in domestic poultry facilities in the 2023 season and inferred their origin from their genotypes.
- From the analysis, it was revealed that the poultry-derived viruses were classified into two types: a genotype that has been detected for three consecutive seasons, and a newly detected genotype that contains genes from viruses derived from wild birds overseas. Four genotypes, including these two genotypes, were detected in wild birds and the environment.
- HPAI outbreaks have occurred in poultry facilities for four consecutive seasons due to emergence and spread of various HPAIV in wild birds. Therefore, we need to be more vigilant against the intrusion of the virus into the domestic poultry farms.
Overview
Eleven HPAI cases have been reported at domestic poultry facilities from November 25, 2023 to April 29, 2024. This is the first time that HPAI outbreak has occurred in four consecutive seasons in Japan.
The NARO continues to monitor the global trend of HPAI epidemic invading Japan by analyzing the whole genomes of these viruses and comparing them with genome information from overseas. For the 2023 season, whole genome analysis of eleven HPAIV strains,including ten H5N1 and one H5N6 subtype strains isolated from poultry was conducted. It was found that they were classified into two genotypes (ten H5N1 subtype strains were G2d-0 and one H5N6 subtype strain was G2c-12). Genotype G2d-0 was also detected in Japan in the 2021 and 2022 seasons. However, G2c-12 is a genotype that was newly detected in the 2023 season, with some gene segments derived from avian influenza viruses (AIV) originated from wild birds overseas.
Similarly, the G2c-12 virus detected in the 2023 season may have emerged because of repeated infections in wild bird populations, resulting in genetic reassortment. Since the virus was not detected in domestic poultry or wild birds during the summer, it is highly unlikely that the same genotype of virus remains in the country. Also, since viruses of the same genotype (G2d-0, G2c-12) were detected in poultry overseas (South Korea) at the same period as the domestic outbreak, it is speculated that these viruses were carried to both countries by migratory birds during the 2023 season.
HPAIV of the H5N5 subtype in addition to H5N1 and H5N6 subtypes, have been detected in 156 environmental samples, including wild birds, wild bird feces, and environmental samples such as lake water, collected by the Ministry of the Environment between October 4, 2023 and April 30, 2024. In the samples of 50 cases analyzed by NARO so far, in addition to the two genotypes of the poultry-derived virus, two more genotypes (G2a-2 and G2d-4: both H5N5 subtypes) have been detected. Therefore, it has become clear that at least four different genotypes of the virus have invaded the country in the 2023 season.
Also, NARO conducted experimental infections to chickens by nasal inoculation, which is the natural infection route, for representative virus strains of two genotypes of the viruses in the poultry outbreak cases. It was revealed from the result that both strains were highly lethal to chickens, with no differences between genotypes. Furthermore, from the estimated amino acid sequence analysis of the viruses detected in poultry during the 2023 season, no mutations were found to be associated with resistance to antiviral drugs or viral adaptation to mammals, except for few viruses. It is thought that there is a low possibility that these virus strains will directly infect humans and cause disease, or that antiviral drugs will be less effective.
Although the number of outbreak cases in poultry facilities in the 2023 season was significantly lower than the 84 cases in the previous season, the number of cases detected in wild birds was the second highest in the past four seasons. Whole-genome sequence analysis of HPAIV showed that poultry-derived viruses in the 2023 season were maintained in wild bird populations flying into the country. It was speculated that the increase in virus concentrations in wild birds and their habitats was one of the factors behind the fourth consecutive outbreaks. As HPAI outbreaks are still being reported around the world, even greater vigilance against virus intrusion into farms is necessary in the future.
For Inquiries
Contact: https://www.naro.go.jp/english/inquiry/index.html
