21.02.2015

Emerg Infect Dis Vol. 21 (5) - May 2015

The novel Eurasian lineage clade 2.3.4.4 highly pathogenic avian influenza (HPAI) A(H5N8) virus spread rapidly and globally during 2014, substantially affecting poultry populations. The first outbreaks were reported during January 2014 in chickens and domestic ducks in South Korea and subsequently in China and Japan, reaching Germany, the Netherlands, and the United Kingdom by November 2014 and Italy in early December 2014.
Also in November 2014, a novel HPAI H5N2 virus was reported in outbreaks on chicken and turkey farms in Fraser Valley, British Columbia, Canada. This H5N2 influenza virus is a reassortant that contains the Eurasian clade 2.3.4.4 H5 plus 4 other Eurasian genes (polymerase acidic protein subunit, matrix protein, polymerase basic protein subunit [PB] 2, nonstructural protein) and 3 North American wild bird lineage genes (neuraminidase [NA], nucleoprotein, PB1). Taiwan has recently reported novel reassortants of the H5 clade 2.3.4.4 with other Eurasian viruses (H5N2, H5N3).
The appearance of highly similar Eurasian H5N8 viruses in Asia, Europe, and now the United States suggests that this novel reassortant may be well adapted to certain waterfowl species, enabling it to survive long migrations. These appearances also represent a major change in Eurasian H5 virus circulation. After the reported spread of HPAI H5N1 virus in Asia, a large, interagency avian influenza virus (AIV) surveillance effort was implemented throughout the United States during April 2006. Of nearly 500,000 wild bird samples tested, none harbored Eurasian subtype H5 AIV. The overall prevalence of AIV was ≈11%, and most viruses (86%) were detected in dabbling ducks (family Anatidae). Although H5N8 subtype viruses have been detected previously in the United States, all have been low pathogenicity AIV of North American wild bird lineage.
The three major findings are(1) the Eurasian lineage of H5N8 clade 2.3.4.4 virus survived introduction into North America in its entirety, (2) the introduction of Eurasian H5N8 into North America appears to be independent from introductions of the virus into Europe, and (3) the duration of circulation of H5N8 virus in the Pacific flyway is unknown, but it was sufficient for reassortment with low-pathogenicity North American lineage wild bird avian flu virus.
Whole-genome sequencing also indicated that the US H5N2 virus was highly similar to recent H5N2 reassortants from British Columbia.