What Animal Did The Spanish Flu Come From
Model too links avian influenza strains to deadly horse flu.
The 1918 flu pandemic caused an estimated 50 million to 100 million deaths worldwide. Credit: CORBIS
The virus that caused the 1918 influenza pandemic probably sprang from North American domestic and wild birds, not from the mixing of human being and swine viruses. A report published today in Nature 1 reconstructs the origins of influenza A virus and traces its evolution and flow through different animal hosts over two centuries.
"The methods we've been using for years and years, and which are crucial to figuring out the origins of gene sequences and the timing of those events, are all flawed," says lead author Michael Worobey, an ecologist and evolutionary biologist at the Academy of Arizona in Tucson.
Worobey and his colleagues analysed more than 80,000 gene sequences from influenza viruses isolated from humans, birds, horses, pigs and bats using a model they developed to map evolutionary relationships between viruses from different host species. The branched tree that resulted showed that the genes of the deadly 1918 pandemic virus are of avian origin.
Birds blamed
Birds take been implicated in the deadly strain's origins earlier. A 2005 genetic analysis of the 1918 pandemic virus pulled from a victim's preserved tissue concluded that it most closely matched viruses of avian origin2. Simply a 2009 written report3 establish instead that the viral genes circulated in humans and swine for at least 2 to 15 years before the pandemic and combined to brand the lethal virus.
Gavin Smith, an evolutionary biologist at Duke-NUS Graduate Medical School at the National University of Singapore, calls the current study "an important contribution to how we analyse information". Smith, a co-writer of the 2009 written report, notes that it identified an avian relationship for two genes in the 1918 virus, only not for 6 genes, as the latest report has washed.
Worobey's study is highly persuasive, says Oliver Pybus, an evolutionary biologist at the University of Oxford, UK. "Information technology shows the evidence for a pig origin is a lot weaker, but it'southward almost impossible to completely shut the door on that."
Many clocks
Scientists use 'molecular clock' models of evolution to piece together relationships amidst organisms by tracking genetic mutations over time. Such models rely on the notion that genetic changes accrue at a reliable rate, like seconds ticking by. Some models assume the rates of molecular evolution are roughly equal, simply there is evidence that the influenza virus evolves at dissimilar rates in different hosts — faster in birds than in horses, for instance. Worobey's model accommodates such a possibility past allowing each host-specific clock to tick independently.
"It's a hitting example of how some model specifications can actually tamper with our reconstructions," says Philippe Lemey, a molecular epidemiologist at the Rega Institute for Medical Research at KU Leuven in Belgium.
The analysis also reveals a shared antecedent for almost all avian flu strains and an H7N7 virus that struck down horses and mules throughout N America in 1872. The panzootic outbreak began in Toronto, Canada, and quickly spread s and due west. Newspapers reported "well-nigh deserted" streets in Washington DC and freight piling up at railroad depots and piers in Philadelphia, Pennsylvania. "Transmission betwixt horses and humans seems to accept been primal to some epidemics when horses were an intimate part of our lives," says Richard Lenski, an evolutionary biologist at Michigan Land University in East Lansing.
"Nosotros now have this thought that the source for a lot of influenza virus we see at present worldwide is potentially equine, whereas the dogma has been for and so long that its avian," says Pybus. "It'due south a fascinating study, and quite a surprise."
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Hoag, H. Study revives bird origin for 1918 influenza pandemic. Nature (2014). https://doi.org/10.1038/nature.2014.14723
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Published:
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DOI : https://doi.org/10.1038/nature.2014.14723
Further reading
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CHANS-Law: preventing the next pandemic through the integration of social and environmental law
International Ecology Agreements: Politics, Law and Economic science (2022)
Source: https://www.nature.com/articles/nature.2014.14723
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