Given all that has happened with the evolution of new HPAI H5 viruses around the world, it is hard to believe we only just passed the 2 year anniversary of the emergence of HPAI H5N8 in South Korea last week (see Jan 17th, 2014 report Media Reporting Korean Poultry Outbreak Due To H5N8).
Up until that time, H5N8 was normally only seen in a low pathogenic form (although one HPAI H5N8 sample had been previously described in China).
Since then we've seen HPAI H5N8 turn up in China, Russia, Europe, Taiwan, and North America. It has spawned multiple high path reassortant viruses in Taiwan (H5N2, H5N3) and North America (H5N1, H5N2), as well as evolving into several genetically distinct clades.
Today the CDC's EID Journal carries a dispatch which finds the H5N8 viruses that returned via migratory birds for the winter of 2014-2015 were different from the ones that had continued to spread through Korean poultry during their absence.
In addition to giving us new insight into the evolution of the H5N8 virus, and its ability to thrive and evolve in the wild aquatic bird population, this is a reminder that the HPAI viruses we know today have the potential to mutate and evolve in faraway nesting grounds and then return the following spring or fall changed in some way.
Change isn't always bad, of course. Viruses can diminish their virulence over time or even fade away completely, crowded out by other - more fit - viruses.
But unlike the ads for Las Vegas, what goes on in avian nesting grounds doesn't necessarily stay in avian nesting grounds. Hence the call for better global surveillance of wild and migratory birds, else we risk being blindsided (again) by a new and potentially virulent avian flu virus.
I've only posted some excerpt, follow the link to read the report in its entirety.
Volume 22, Number 3—March 2016
DispatchHighly Pathogenic Avian Influenza A(H5N8) Viruses Reintroduced into South Korea by Migratory Waterfowl, 2014–2015
Highly pathogenic avian influenza A(H5N8) viruses were isolated from migratory waterfowl in South Korea during fall 2014–winter 2015, a recurrence after initial introduction in winter 2014. These reappeared viruses were phylogenetically distinct from isolates circulating in poultry farms in South Korea.Since the Asian-lineage subtype H5 highly pathogenic avian influenza (HPAI) virus was first detected in China in 1996, outbreaks of infection caused by this virus in poultry have been continuous. The HPAI (H5) viruses have evolved and continue to evolve into many genetic lineages and multiple clades (1). In January 2014, novel reassortant HPAI viruses of subtype H5N8, clade 18.104.22.168, were detected in poultry and wild bird carcasses in South Korea (2). Closely related viruses were also detected in Japan (3) and China (4). Genetic analysis showed that this virus was generated by reassortment of HPAI viruses of eastern China.
Subsequently, HPAI (H5N8) viruses spread to Europe and North America and were then reintroduced into South Korea and Japan (5). The HPAI (H5N8) viruses identified in South Korea in early 2014 were divided into groups A (A/Baikal teal/Korea/Donglim3/2014 strain-like) and B (A/breeder duck/Korea/Gochang1/2014-like). Group A viruses further evolved into 3 distinct subgroups: icA1 (Europe/Japan), icA2 (North America/Japan), and icA3 (South Korea/Japan) (5). Wild birds were suspected of being a source of intercontinental transmission because the timing and direction of the outbreak coincided with the migratory route of wild birds (5,6).
We sequenced and genetically analyzed the complete genomes of 11 HPAI (H5N8) viruses isolated from wild migratory waterfowl in South Korea during December 2014 and February 2015 and compared these isolates with other HPAI (H5N8) isolates, including isolates identified from South Korea poultry farms in late 2014.
These results suggest that HPAI (H5N8) viruses circulated in wild bird populations and evolved into subgroups during the breeding season. Detection of subtype H5N8 viruses in healthy wild birds (12,13; this study) and subclinical infection with viral shedding among migratory waterfowl experimentally infected with HPAI (H5N8) viruses (11) support the theory of long-term circulation of HPAI (H5N8) viruses in wild bird population.
This study also found that subtype icA3 viruses, derived from HPAI (H5N8) viruses from South Korea and reintroduced by migratory waterfowl, were genetically distinct from the HPAI (H5N8) viruses that continued to circulate in poultry farms. In the previous 4 HPAI (H5N8) virus outbreaks in South Korea and Japan, migratory waterfowl were identified as the source of HPAI outbreaks (14,15); however, related HPAI viruses were not reintroduced into South Korea and Japan after the initial outbreak season. The phylogenetic analysis described here shows that HPAI (H5N8) viruses isolated from migratory wild birds in the winter of 2014–15 are phylogenetically distinct from isolates from South Korean poultry farms. HPAI (H5N8) viruses thus independently evolved in wild bird populations and poultry farms in South Korea until late 2014.
Our results indicate that HPAI (H5N8) viruses have been circulating in wild waterfowl population since early 2014. Enhanced global active surveillance is needed to monitor the spread of these viruses through wild birds. Such efforts could clarify the epidemiology of HPAI virus and facilitate early recognition of novel genotypes.