Note: For those over 40, a `mashup’ is a new work (often audio or video) created by combining existing components in a new way.
The scientific term is `reassortment’, but I’ve used the word `mashup’ here in an vain attempt to prove that I’m still young, `hip’, and `with it’.
Today we get a speculative article from the AP that asks what happens if the new A/H1N1 virus and the H5N1 bird flu virus combine?
While no one knows how likely this is to happen, or what kind of offspring it might produce, there is no denying that many scientists are concerned over the possibility of a viral reassortment.
First this article from the AP - which has some good quotes from such notable scientists as Robert Webster, Michael Osterholm, and Malik Peiris - then some discussion of genetic mashups (reassortments).
Friday, May 08, 2009
MEXICO CITY — Bird flu kills more than 60 percent of its human victims, but doesn't easily pass from person to person. Swine flu can be spread with a sneeze or handshake, but kills only a small fraction of the people it infects.
So what happens if they mix?
This is the scenario that has some scientists worried: The two viruses meet — possibly in Asia, where bird flu is endemic — and combine into a new bug that is both highly contagious and lethal and can spread around the world.
Scientists are unsure how likely this possibility is, but note that the new swine flu strain — a never-before-seen mixture of pig, human and bird viruses — has shown itself to be especially adept at snatching evolutionarily advantageous genetic material from other flu viruses.
Theoretically, any host (human, pig, etc) that is capable of being infected by two different influenza viruses at the same time, is capable of becoming a `mixing vessel’ and produce a new hybrid virus.
Pigs, which are susceptible to avian, human, and swine influenza strains are considered to make particularly good `mixing vessels’.
For reassortment to happen, two influenza viruses would have to invade the same cell – at the same time – swap gene segments in such a way as to produce a `fit’ virus, and then burst out of the cell as this new `reassorted’ virus.
Image from the Baylor College of Medicine.
This reassorted virus would then have to compete with the millions of other copies of the two original viruses in the host. So successfully combining at the cellular level isn’t enough to introduce a new virus to the world.
That virus must survive, replicate well, and go on to efficiently infect other hosts.
By looking at the genetics of viruses, we can tell that this sort of reassortment does happen. What we don’t know is how likely it is to happen between the newly emerging H1N1 virus and the bird flu virus.
There are a couple of troubling indicators, however.
A recent study out of Kobe University in Japan found that 10% of pigs tested in 4 Indonesian provinces carried the H5N1 bird flu virus (or perhaps antibodies, it is difficult to tell from this article).
Posted on Thursday 30 April, 2009 12:14 PM
Study shows new H5N1 strain may mutate in pigs
The Yomiuri Shimbun
A high proportion of pigs in Indonesia carry the highly infectious H5N1 avian influenza virus–something that could mutate into a new strain inside the pigs, according to research by the Kobe University Center for Infectious Diseases.
It is feared that if the virus mutates inside pigs and becomes transmittable between humans, it could pose a far greater threat to people than the current outbreak of swine flu.
“It’s a surprising result,” said Yoshiyuki Nagai, director of the Center of Research Network for Infectious Diseases. “Perhaps we are looking at the process by which a new strain of influenza becomes infectious. We need to be vigilant.”
(Apr. 30, 2009)
The new A/H1N1 virus is a human-adapted swine flu virus, which originated in pigs, and has been shown to infect pigs in its present state. Thus setting the stage for the likely meet-up of these two viruses somewhere in the world in a susceptible host.
What happens then, however, is unknown.
Do we end up with a `Frankenswine’ virus, one that picks up virulence and retains its transmissibility?
But it is also possible that we end up with a less fit virus, or no reassortment at all.
The reassortment of influenza viruses is always concern for scientists, and they will be watching for any signs of changes to either virus, particularly as the H1N1 virus spreads in places like Egypt and Indonesia, where the H5N1 virus is endemic.
Of course, the H1N1 virus could pick up mutations from other influenza viruses as well, and will be watched carefully over the summer as it spreads in the southern hemisphere.
For those seeking some reassurance, the seasonal H1N1 virus (which, can also infect pigs) has had many opportunities to meet up with the bird flu virus over the past 10 years, and so far at least, hasn’t managed to produce a sustainable `mashup’.
Of course, this new Swine flu virus is genetically different from the seasonal strain, and so - as the saying goes - past performance is no guarantee of future results.