Via Nature News & Comment, Declan Butler brings us a highly informative report: Novel deadly bird flu virus kills two in China. Excerpt (but read the whole thing, and follow him on Twitter):
The new virus, in other words, seems to stem from reassortment of three virus strains that purely infect birds -- in contrast with the 2009 H1N1 pandemic virus, which was a mix of viruses that infect birds, pig and humans.
Most of the genetic analyses are still being carried out confidentially within WHO's global flu research networks. But some researchers, such as a team at the University of Edinburgh, have also started posting their preliminary analyses online.
A striking feature of the novel virus is that its H protein is structurally similar to that of viruses that don’t cause severe sickness in birds, and different from those that do, such as the H5N1 virus that has been ravaging poultry flocks in Asia since late 2002.
Flu viruses that don’t sicken birds can, however, cause severe disease in humans simply because we lack any immunity to them. They also may be more lethal in people depending on how they bind to receptors in the human airways.
Though analysis is in early days, scientists say it seems clear from the sequence that the novel virus has acquired key mutations that permit the H protein to latch onto receptors on mammalian cells in the airways instead of avian receptors. The virus also contains several other genetic variations that are known from past studies in mice and other animals to cause severe disease.
Initial data suggest, too, that the virus is affecting cells deep in the lung, which would fit with a picture of a virus -- much like that of the novel coronavirus (see Nature 495, 149–150 (2013)) – that can cause severe disease. But it may also indicate a virus that doesn’t spread as easily as one that affects the nose and throat and can thus be coughed and sneezed out more readily.
Still, the full pattern of receptor binding has yet to be worked out, cautions Peiris.
Silent spreader?
The fact that the virus appears not to sicken birds has potential epidemiological, and possibly public health, implications, Peiris adds. It could be spreading in poultry undetected -- and thus could create a reservoir of infection that would lead to frequent sporadic human infections that crop up without warning.
A highly pathogenic virus like H5N1 is easy to spot as it wipes out flocks -- and can then be controlled by extended culling. But it might be next to impossible to control a virus in birds that offers few visible symptoms, says Peiris. "That really would be quite a problem,” he says. "The question is whether it's already too late to stamp out or not."
Indeed, China has not reported any recent H7 flu infections in birds, perhaps because such infections would not show up as serious disease, or maybe because of shortcomings in surveillance or reporting. A key need now, Peiris says, is to track down which birds or animals the affected humans caught the virus from.By the way—here's the home page of that Edinburgh link. It's an important resource, and not just for H7N9. I'm putting it in the Journals and Technical Sources list, down in the middle column.
