Date Published: January 6, 2015
Source: Proceedings of the National Academy of
Sciences of the United States of America
Institutions Involved: US Geological Survey, Western Ecological Research Center, Patuxent Wildlife Research Center, and Avian Influenza Program.
Institutions Involved: US Geological Survey, Western Ecological Research Center, Patuxent Wildlife Research Center, and Avian Influenza Program.
Summary: A study was conducted through a
phylogeographic approach to prove how the timing of the pathogenic avian influenza virus (bird flu) H5N1 outbreaks
and viral gene migrations are connected to the bird migration network.
The first outbreak
of the highly pathogenic avian influenza (HPAI) H5N1, occurred in 1996 in Asia
and then spread into areas such as the Middle East, Africa, and most parts of
Europe. In this study, the authors of this research used bird migration, timings
of the H5N1 outbreaks, and the viral hemagglutinin (HA) gene ,and whole-genome
nucleotide sequences. They used these to analyze the link shared with the
migration of the birds and viral gene flow to the outbreaks of the HPAI H5N1
virus in these various locations.
With the help of the
GPS the authors of this research were able to track bird migration routes of
four particular species; the bar-headed goose and ruddy shelduck (along the
Central Asian (CA) flyway) and the swan goose and northern pintail (along the
East Asian-Australasian (EA) flyway).
Based on the
chronology of the HA gene, researchers created a phylogenetic tree to
investigate the link between the migration network of birds and viral spread.
With the help of randomized tests, the authors observed a strong gene flow in both the EA and CA
flyways. In this research two particular HPAI H5N1 clades from the phylogenetic
tree were highlighted: 2.3.2 and 2.3.2.1. These clades were built based on the
viral HA gene. The results showed a strong genetic proximity with similar
isolation periods of the virus and the geographical regions where the outbreaks
occurred. Researchers believe that the migrating birds carried the ancestor
viruses and over time spread them in regions along the flyways.
To further prove
their theory, the authors performed the two-tailed t test, which resulted in a p-value of 0.01: a p-value less than
or equal to 0.05 allows researchers to reject the null hypothesis and accept
the alternative hypothesis. And in this case, the results refuted the theory of
random mixing of flyways and further proved that migratory flyways are
essential in playing the role of a barrier to the intracontinental spread of
H5N1. In both flyways, the observed gene flow was best observed through bird
migration routes. The factor of spatial distance, however, was proved not to be
an ecological barrier to gene transfer in flyways.
The analysis and
research done proved that the migratory routes of the birds and the outbreaks
of the HPAI H5N1 essentially share the same migration network. Thus, it was
concluded that the area in which the clades were spread shared a similar
geographic pattern as the routes of the migratory birds.
Citation:
Huaiyu, T., Zhou,
S., Dong, L., Boeckel, T. P. V., Cui, Y., Wu, Y., Cazelles, B., Huang, S.,
Yang, R., Grenfell, B. T., and B. Xu. 2015. Avian influenza H5N1 viral and bird
migration networks in Asia. Proceedings of the National Academy of Sciences of
the United States of America. 112(2): 172-177.
This knowledge proves to be very useful concerning the spread of pandemics, especially ones discussed as widely as Avian flu. Although the disease did not ultimately have much impact in the United States during its initial breakout, one could still utilize this study to both prevent future outbreaks and quarantine existing outbreaks, not just limited to H5N1.
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