We’ve often discussed the potential for pigs (and other hosts) to be infected by more than one flu virus, which might create an opportunity for the viruses to swap genetic material – or reassort – resulting in a new, hybrid virus.
While we’ve known this happens (albeit, rarely) in swine, the evidence for duel influenza `A’ infection in humans has been less robust.
Duel infections have been noted, but usually with an `A’ and a `B’ virus. In 2008, we learned of an Indonesian teenager who tested positive by RT-PCR for both H5N1 and the seasonal flu strain H3N2 as reported by Maryn McKenna on CIDRAP.
Which shows that while rare, co-infection with two influenza `A’ viruses can occur.
Today we’ve a study out of New Zealand that suggests that co-infections in humans by influenza `A’ strains may be more common than previously believed.
Matthew Peacey , Richard J. Hall, Stephanie Sonnberg, Mariette Ducatez, Shevaun Paine, Mackenzie Nicol, Jacqui C. Ralston, Don Bandaranayake, Virginia Hope, Richard J. Webby, and Sue Huang
Co-infection with seasonal influenza A (H1N1) and pandemic (H1N1) 2009 could result in reassortant viruses that may acquire new characteristics of transmission, virulence, and oseltamivir susceptibility. Results from oseltamivir-sensitivity testing on viral culture suggested the possibility of co-infections with oseltamivir-resistant (seasonal A [H1N1]) and -susceptible (pandemic [H1N1] 2009) viruses.
While you’ll want to read the EID Journal dispatch, briefly the story is:
During the opening days and weeks of the pandemic in 2009, clinical samples in New Zealand were first screened for Influenza A, and then if positive, tested for the novel H1N1 virus.
Testing for seasonal H1N1 and seasonal H3N2 were only done if a sample tested positive for influenza A, but negative for the pandemic virus.
Unexpectedly, some viral cultures that tested positive for novel H1N1 also appeared to show resistance to oseltamivir (Tamiflu).
Further investigation revealed that the pandemic virus was not resistant, that the samples contained both novel H1N1 and a resistant seasonal H1N1 virus.
A serendipitous discovery that led researchers to conduct secondary rRT-PCR testing for seasonal H1N1 on 1,044 clinical samples that had already tested positive for the pandemic virus.
Among those, Eleven co-infections were detected, for a rate of 1.1%.
Two additional samples were believed to represent co-infections, but a definitive determination was not possible.
The authors state that the rate of co-infection could actually be higher, since samples were not checked for any other flu strains such as H3N2 and influenza B.
While gene swapping is possible under a co-infection scenario, it isn’t by any means assured. And even should a reassortment take place, the resulting virus might not prove biologically `fit’.
Still, this research suggests that humans, like swine, could be `mixing vessels’ for influenza. How often this sort of gene swapping actually occurs in humans remains unknown.
The New Zealand press has a report on this study, which you can read at the link below: