The emergence and diversification of panzootic H5N1 influenza viruses

Abstract

The Asian highly pathogenic avian influenza H5N1 virus was first detected in the goose population of Guangdong, China in 1996. The viruses in this lineage are unique in their ecological success, demonstrating an extremely broad host range and becoming established in poultry over much of Asia and in Africa. H5N1 viruses have also diverged into multiple clades and subclades that generally do not cross neutralize, which has greatly confounded control measures in poultry and pre-pandemic vaccine strain selection. Although H5N1 viruses currently cannot transmit efficiently between mammals they exhibit high mortality in humans and recent experimental studies have shown that it is possible to generate an H5N1 virus that is transmissible in mammals. In addition to causing unprecedented economic losses, the long-term presence of the H5N1 virus in poultry and its frequent introductions to humans continue to pose a significant pandemic threat. Here we provide a summary of the genesis, molecular epidemiology and evolution of this H5N1 lineage, particularly the factors that have contributed to the continued diversification and ecological success of H5N1 viruses, with particular reference to the poultry production systems they have emerged from.

Diversity and evolution of avian influenza viruses in live poultry markets, free-range poultry and wild wetland birds in China

“…Although large-scale surveillance of AIVs had been undertaken in southern China, including Zhejiang province, particularly following the outbreak of H5N1 and H7N9 AIVs in humans (Guan & Smith, 2013;Su et al, 2015;WHO, 2015), Hubei province in central China seems less affected by AIVs (Su et al, 2015 . Although this subtype is also found in Zhejiang, the viruses from these two provinces are genetically distinct, indicative of a relatively long time period of separation.…”

“…Although the successful cross-species transmission of AIVs to become fully adapted human pathogens occurs rarely (Kuiken et al, 2006), the spillover of AIVs into human populations in the absence of ongoing transmission is a more regular occurrence, and is responsible for sporadic and often fatal respiratory disease. This process is exemplified by human cases of highly pathogenic H5N1 that have occurred since 1997 (Claas et al, 1998;Guan & Smith, 2013) and the more recent (2013) emergence of H7N9 in China (Gao et al, 2013;Su et al, 2015), both of which are associated with mortality rates w40 %. Clearly, such viruses could pose a significant threat to public health if they become adapted to human respiratory and contact transmission .…”

“…During the past two decades many novel AIVs infecting poultry have emerged in China, including those that cause human disease (Claas et al, 1998;Butt et al, 2005;Gao et al, 2013;Guan & Smith, 2013;Wei et al, 2013;Chen et al, 2014;Su et al, 2015;Yang et al, 2015). Interestingly, almost all of these human-infecting AIVs are prevalent in live poultry markets (LPMs) in southern China, a locality often regarded as an 'epicenter' of influenza genetic diversity and emergence (Guan & Smith, 2013).…”

“…Interestingly, almost all of these human-infecting AIVs are prevalent in live poultry markets (LPMs) in southern China, a locality often regarded as an 'epicenter' of influenza genetic diversity and emergence (Guan & Smith, 2013). Indeed, the large numbers of LPMs in this region serve as important vessels for the mixing of and reassortment amongst multiple subtypes of AIVs, in turn increasing viral genetic diversity (Liu et al, 2003).…”

Epidemiology, Evolution, and Recent Outbreaks of Avian Influenza Virus in China

“…China is recognized as a geographical area with suitable conditions for the emergence of novel influenza viruses (2). New strains of AIVs currently widely circulate in China, occasionally resulting in human infections.…”