Up until three years ago, the role of migratory birds in the long distance spread of HPAI H5N1 was hotly debated, with the rallying cry that `Sick birds don’t fly’ used to argue that migratory birds aren’t to blame for the spread of the virus (see India: The H5N1 & Migratory Birds Debate).
Despite a growing body of evidence to the contrary, as recently as 2015 the UN CMS/FAO Co-Convened Scientific Task Force on Avian Influenza and Wild Birds argued that typically the `spread of HPAI virus is via contaminated poultry, poultry products and inanimate objects although wild birds may also play a role'.
The great leap of HPAI H5N8 from Asia to North America in 2014-15, and the introduction of HPAI H5N8 to Europe, the Middle East, and Africa in 2016-17, have pretty much cemented the role of migratory birds in spreading HPAI viruses across long distances (see Migratory Birds & The Spread Of Highly Pathogenic Avian Flu).
Last fall we saw a freshly reassorted HPAI H5N6 virus turn up in both northern Europe and Japan within three weeks of each other, and last summer HPAI H5N8 crossed the equator and established a new home in South Africa.Understanding how avian flu viruses are transmitted; when, where, and by what types of birds is therefore of great importance. It could even lead to `high risk' forecasts for poultry interests along the migratory flyways, or perhaps provide an early warning of potential reassortment events in the making.
Long time readers of this blog will remember that in January of 2015 in H5N1 Detected In Swan Die Off In Henan Province, we saw a report on the discovery of nearly 100 dead birds (swans & ducks) at the Sanmenxia reservoir in Henan province, which authorities attributed to the H5N1 virus
Sanmenxia reservoir is a major overwintering habitat for a variety of waterfowl migrating between China, Mongolia, and Siberia.
Eight months later, in Novel H5N1 Reassortment Detected In Migratory Birds - China, we looked at a Scientific Reports research article that determined the H5N1 virus recovered at Sanmenxia was a novel reassortant, possessing a Clade 18.104.22.168c HA gene and a H9N2-derived PB2 gene.
The authors wrote:
Sanmenxia Clade 22.214.171.124c-like H5N1 viruses possess the closest genetic identity to A/Alberta/01/2014 (H5N1), which recently caused a fatal respiratory infection in Canada with signs of meningoencephalitis, a highly unusual symptom with influenza infections in humans. Furthermore, this virus was shown to be highly pathogenic to both birds and mammals, and demonstrate tropism for the nervous system.As it turns out, Sanmexia reservoir has been well monitored since at least 2010 because it is a well established stopping off place for migratory birds, and researchers were able to determine the flight paths taken by bird coming to and leaving the region.
Today they present evidence for HPAI H5N1 being transmitted between China and Mongolia via migratory whooper swans. I've only posted some excerpts from a much longer article, you'll want to follow the link to read the entire report.
Migratory Whooper Swans Cygnus cygnus Transmit H5N1 Virus between China and Mongolia: Combination Evidence from Satellite Tracking and Phylogenetics Analysis
Shuhong Li, Weiyue Meng, Dongping Liu, Qiqi Yang, Lixia Chen, Qiang Dai, Tian Ma, Ruyi Gao, Wendong Ru, Yunfeng Li, Pengbo Yu, Jun Lu, Guogang Zhang, Huaiyu Tian, Hongliang Chai & Yanbing Li
Scientific Reportsvolume 8, Article number: 7049 (2018) doi:10.1038/s41598-018-25291-1
Received:26 January 2018 Accepted:17 April 2018 Published online: 04 May 2018
In late 2014, a highly pathogenic avian influenza (hereafter HPAI) H5N1 outbreak infected whooper swans Cygnus cygnus wintering at the Sanmenxia Reservoir area, China, and raised concerns about migratory linkages between wintering and breeding grounds of whooper swans.
In this study, 61 swans were satellite tracked from 2013 to 2016 to determine the spatial association of their migration routes and H5N1 outbreaks, and 3596 fecal samples were collected along the migration routes for virology testing. Swans departed the wintering grounds and migrated along the Yellow River, and flew over the Yin Mountains in China.
The Brownian bridge movement model showed there was a high degree of spatiotemporal overlap between the core use area along the spring migration pathway and historical H5N1 events in China and Mongolia from 2005 to 2015.(Continue . . . )
The H5N1 strain was isolated and phylogenetic analyses confirmed that the HA gene sequence generated is genetically similar to that of the epidemic strain at a previous wintering site (the Sanmenxia Reservoir area) along its flyway. Our results identified a previously unknown migratory link of whooper swans in central China with Mongolia and confirmed that the swans could carry the HPAI H5N1 virus during migration, resulting in long-distance transmission.
For more on the tracking of migratory birds and their role in the spread of both HPAI and LPAI viruses, you may wish to revisit:
Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1
HPAI H5N1 Clade 126.96.36.199c Virus in Migratory Birds
Alaska Still A Likely Portal For Introduction Of Avian Viruses
Genetic Evidence Of The Movement Of Avian Influenza Viruses From Asia To North America