Swine Flu Outbreak Illuminated By Avian Flu Research

ScienceDaily (Apr. 30, 2009) — A new study by University of Maryland researchers suggests that the potential for an avian influenza virus to cause a human flu pandemic is greater than previously thought. Results also illustrate how the current swine flu outbreak likely came about.

As of now, avian flu viruses can infect humans who have contact with birds, but these viruses tend not to transmit easily between humans. However, in research recently published in the Proceedings of the National Academy of Sciences, Associate Professor Daniel Perez from the University of Maryland showed that after reassortment with a human influenza virus, a process that usually takes place in intermediary species like pigs, an avian flu virus requires relatively few mutations to spread rapidly between mammals by respiratory droplets.
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Though it comes from a different strain of avian flu than the one that contributed to the hybrid virus now causing the swine flu outbreak, Perez's research virus is similar in origin to the swine flu virus, in that both involved a combination of avian and human influenza viruses.

Perez infected ferrets (considered a good model for human influenza transmission) with the virus he created, and allowed the virus to mutate in the species. Before long, healthy ferrets that shared air space but not physical space with the infected ferret had the virus, showing that the virus had mutated to spread by respiratory droplets.

When the genetic sequences of the mutant virus and original hybrid virus were compared, the only differences were five amino acid mutations, three on the surface, and two internally. Two of the surface mutations were determined to be solely responsible for supporting respiratory droplet transmission. Because so few mutations were necessary to make the hybrid H9N2 transmissible this way, they concluded that after an animal-human hybrid influenza virus forms in nature, a human pandemic of this virus is potentially just a few mutations away.

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"This is just the tip of the iceberg," said Perez. "Many more studies have to be done to see which combinations of mutations cause this type of transmission before we can design the appropriate vaccines."

Perez will be talking this week with the NIH and the CDC to discuss his team's role in researching the current swine flu virus strain. Perez will likely do studies related to vaccine development, virus transmission between humans and animals, and the pathogenesis of the virus.

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