Abstract
Highly pathogenic avian influenza (HPAI) is essentially a poultry disease. Wild birds have traditionally not been involved in its spread, but the epidemiology of HPAI has changed in recent years. After its emergence in southeastern Asia in 1996, H5 HPAI virus of the Goose/Guangdong lineage has evolved into several sub-lineages, some of which have spread over thousands of kilometers via long-distance migration of wild waterbirds. In order to determine whether the virus is adapting to wild waterbirds, we experimentally inoculated the HPAI H5N8 virus clade 2.3.4.4 group A from 2014 into four key waterbird species—Eurasian wigeon (Anas penelope), common teal (Anas crecca), mallard (Anas platyrhynchos), and common pochard (Aythya ferina)—and compared virus excretion and disease severity with historical data of the HPAI H5N1 virus infection from 2005 in the same four species. Our results showed that excretion was highest in Eurasian wigeons for the 2014 virus, whereas excretion was highest in common pochards and mallards for the 2005 virus. The 2014 virus infection was subclinical in all four waterbird species, while the 2005 virus caused clinical disease and pathological changes in over 50% of the common pochards. In chickens, the 2014 virus infection caused systemic disease and high mortality, similar to the 2005 virus. In conclusion, the evidence was strongest for Eurasian wigeons as long-distance vectors for HPAI H5N8 virus from 2014. The implications of the switch in species-specific virus excretion and decreased disease severity may be that the HPAI H5 virus more easily spreads in the wild-waterbird population.
Highlights
Avian influenza viruses—in particular highly pathogenic human infections caused by the Highly pathogenic avian influenza (HPAI) H5N1 virus and avian influenza (HPAI) viruses—form a continuous threat with the spillover of HPAI H5N1 virus to wild birds
All four duck species became infected with HPAI H5N8 virus, 63% (20/32) of the ducks according to virus isolation and 100% (32/32) of the ducks according to RTPCR (Table 1)
The number of ducks that became infected according to virus isolation differed among species: Eurasian wigeons and common teals were more often found to be infected with HPAI H5N8 virus than mallards and common pochards
Summary
Avian influenza viruses—in particular highly pathogenic human infections caused by the HPAI H5N1 virus and avian influenza (HPAI) viruses—form a continuous threat with the spillover of HPAI H5N1 virus to wild birds. Since the emergence of the HPAI H5N1 sified into multiple genetic lineages (“clades”); more virus in the poultry in China in 1996, H5 HPAI viruses recently, reassortment between the HPAI H5N1 virus and that share a common ancestral virus (A/goose/Guang- the low pathogenic avian influenza (LPAI) viruses resulted dong/1/96 [GsGd]) have continued to cause outbreaks in in HPAI viruses with neuraminidase (N) genes (N1, N2, N5, N6, and N8) and other genes of LPAI virus origin[2,3,4,5]. Within Europe, HPAI H5N1 GsGd virus has been detected in multiple countries in 2004 (clade 1), 2005/ 2006/2007 (clades 2.2 and 2.2.1), and 2008/2009/2010. In November and December of 2014, the HPAI H5N8 GsGd virus (clade 2.3.4.4, group A, Buanlike)[8] was detected in wild birds and poultry in various countries of Asia, Europe, and—for the first time—North America. The global spread of HPAI H5N8 virus in 2014/ 2015 raises the question whether this H5 virus was better adapted to wild birds (i.e., increased virus replication and transmission combined with decreased virulence, resulting in better virus survival in wild bird populations) than the HPAI H5 virus from before 2014/2015
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