H7N9 Influenza: History of Similar Viruses Gives Cause for Concern
The H7N9 avian flu strain that emerged in China earlier this year has subsided for now, but it would be a mistake to be reassured by this apparent lull in infections.
The virus has several highly unusual traits that paint a disquieting picture of a pathogen that may yet lead to a pandemic, according to lead scientists from the National Institute of Allergy and Infectious Diseases. David Morens, Jeffery Taubenberger, and Anthony Fauci, in a paper published in mBio®, the online open-access journal of the American Society for Microbiology, describe the history of H7 viruses in animal and human disease and point out that H7 influenza has a tendency to become established in bird, horse, and swine populations and may spillover repeatedly into humans.
“The evidence as a whole is complex and the implications of past outbreaks for predicting the future course of the current H7N9 epizootic [an epidemic among animals] are uncertain,” write the authors.
The outbreak of H7N9 earlier this year led China to temporarily close scores of live poultry markets in an effort to limit the spread of the virus. Although this previously unrecognized strain of avian influenza A has now been associated with 132 confirmed human infections and 39 related deaths (as of June 14), the rate at which new cases are recognized has dwindled in recent weeks.
In their minireview, Morens, Taubenberger and Fauci point out that despite this apparent hiatus, viruses like H7N9, which have subtype 7 hemagglutinin, are a cause for heightened concern because of several highly unusual characteristics. First, H7 viruses have repeatedly been involved in numerous explosive poultry outbreaks including incidents in New York, Canada, Mexico, the Netherlands, and Italy, and in almost all of these cases the virus eventually spilled over into humans. Also, H7 viruses have the ability to mutate from a low pathogenicity form to a high pathogenicity form in birds, a scenario that can lead to large-scale culling and ultimately to human exposure to the virus among poultry workers.