Bad news and- sort of- good news about the H7N9 bird flu

There's good news and bad news on the flu front.

The bad news is that: the H7N9 "bird flu-" one of the most lethal strains ever known- has jumped from mainland China to Taiwan.

The good news- sort of- is that people will have a hard time catching it from other people.Catching it from birds, on the other hand, is another matter.

"H7N9" refers to two proteins which come in several varieties in flu viruses."H" stands for hemagglutinin, which enables the virus- which is not in itself a living entity and needs to infect a cell-in order to reproduce-to bind to that virus. There are 17 known varieties of influenza hemagglutinin, each assigned a number.

There are nine known varieties of influenza neurominidase (the "N" in H7N9), which enables the virus to spread through the respiratory system. Only N1 and N2 have been implicated in human influenza epidemics, though isolated cases of human infection have previously occured from viruses with neurominidases 3 through 7, It's obviously unusual for an outbreak of human flu to be N9.

Human influenza viruses have hemmaglutinins numbered one through 3. H1N1, for example, is readily transmitted from person to person. But viruses with hemmaglutinins four through 17 don't pass readily from human to human. They probably have to be contracted from some other animal- in this case, most likely birds (pigs also are notorious reservoirs for flu viruses affecting humans).

So as deadly as the H7N9 flu is, it could be a lot worse. We might get it from a bird, but it's unlikely (though not impossible) for us to transmit it to each other.

On the other hand,  this is an N9, and even if it's moving thorough a vector, at this point it clearly is an outbreak among humans, though not between them.

HT: Drudge