And so, the winner of “What will today’s topic be” is one of my favorite topics of conversation - Avian Influenza!
That man who flew around on all those planes while infected with XDR-TB (the hard core tuberculosis), he’s getting a great deal of attention, and rightly so (he’s very sorry about it all), but there’s something we’re not hearing so much about, and that something would be the new human bird flu infections in Wales.
Wales is a tiny country inside of, like, England. Forgive me, I’m terrible at geography. And I’m being a bit facetious. Wales isn’t inside England. It’s inside the United Kingdom, right next to England.
A bit about bird flu. O my, wherever do I start?
Bird flu, or avian influenza, is a disease of birds that sometimes infects other species. It is caused by a virus. All human influenza virus is thought to have originated in birds, later adapting to human hosts.
This adaptation of influenza, this jumping from bird species to other species, particularly mammals, particularly particularly the human species, this is the behavior that has everyone so concerned.
Now, there are three kinds of influenza viruses that infect humans: A, B, and C. The kind we’re concerned with, when we talk about avian influenza, is influenza A.
Here are some important clarifications. Bird flu, or avian influenza, should refer only to influenza found primarily in birds; bird flu is a disease of birds. Bird flu can and does infect other animals, but it is most happy in, ie, most well adapted to, birds.
If someone comes up to you and starts talking about “that bird flu,” they’re probably referring to H5N1. H5N1 is the strain of influenza A, avian influenza, that’s been getting most of the attention these days. It’s this strain that the world is watching most closely, fearing it could lead to the next pandemic. H5N1 has been making itself quite at home in all sorts of mammals, including humans, and what the world is afraid of is H5N1 making the jump from being a bird influenza to being a human influenza.
Human influenza, a/k/a the flu, passes through every year, as I’m sure you’re aware. Most of us survive it just fine, but every few decades, a particularly nasty version comes along, one our immune systems aren’t used to, or one that’s not so used to playing with people. When this happens, we call it an influenza pandemic. If H5N1 were to become a human influenza, and spread efficiently from person to person to cover the globe, then we’d be in the midst of an influenza pandemic, or, as some like to call it, panflu.
During panflu, many more people die than during regular flu season. Around 1918, we had a pretty nasty panflu, sometimes called “Spanish Flu,” and millions of people died, with estimates of up to 100 million. The CFR, or case fatality rate, for those infected in the United States is estimated to have been about 2%, which doesn’t seem so bad, but 2% was enough to have bodies piling up in the streets. 2%…2% sucks. (Please see below for links re 1918 and CFR).
H5N1’s CFR is over 50% right now; H5N1’s CFR in Indonesia is over 70%.
Now, back to the bird flu, me-and-you flu basics. Just think: bird flu likes to date birds, but will sometimes stray, human flu is really into dating people.
Also, flu is slutty, where slutty = easily transmissible within host populations. Like, it is easy to catch influenza from someone you’re sitting next to on a plane. It’s not as easy to catch, say, venereal warts from someone you’re sitting next to on a plane.
Should I not have mentioned venereal warts on this, our first official day together? Ah well. Might as well get used to it.
Where was I? Flu, flu, kinds of flu.
There are many different kinds of influenza A, determined by type of two glycoproteins found on the surface of the virus - hemagglutinin (HA or H, for our purposes) and neuraminidase (NA or N, for our purposes).
Each little influenza A virus particle, called a virion, has both H and N on its surface.
There are 16 different kinds of hemagglutinin, and 9 kinds of neuraminidase. When we refer to H5N1, it means that the virus has the H5 kind of hemagglutinin, and the N1 kind of neuraminidase.
As you can see, there are many possible H and N combinations. I’m gonna let CIDRAP speak for me now:
“Human disease historically has been caused by three subtypes of HA (H1, H2, and H3) and two subtypes of NA (N1 and N2). H1 and H3 are the subtypes that currently cause seasonal influenza in human populations around the globe each year.
More recently, human disease has been recognized to be caused by additional HA subtypes, including H5, H7, and H9. Such cases have predominantly been associated with exposure to infected birds. Person-to-person transmission has occurred in a few isolated situations.”
So, whenever people are found to have been infected by an H5, H7, or H9, scientists are a bit concerned, because it’s not the kind of flu our bodies are used to dealing with, so we don’t have the same sort of immunity.
Note how CIDRAP says, in that second paragraph, “Person-to-person transmission has occurred in a few isolated situations.” Doesn’t sound so bad, right? But, it’s sorta bad. And it seems to be what’s going on in Wales right now. Not with H5N1. In Wales, we’ve got H7N2 circulating through the local human population. Now, nobody’s dying, like they are when they catch H5N1, but these things can change, quickly, as the virus mutates.
H7N2 in Wales.
Pros
1) Not killing people.
2) We’re aware of it.
Cons
1) Seems to be spreading pretty well between people.
2) Since it’s not killing people, only making them mildly to moderately ill, it’s harder to track, since infected people might just think they have a cold or pink eye or the regular old flu.
Gosh, this is a whole lotta info, isn’t it? Is it too much to start with? I think I’ll stop for today, and leave you with a lovely illustration of an influenza A virion.
It’s not the most darling picture I could find, but it is in the public domain. The, like, government made it. Or something.
To be continued…
ps - CIDRAP = Center for Infections Disease Research and Policy
pps - lipid envelope = hot!
ppps - here are those links I promised re CFR and 1918:
Flu Pandemic Morbidity/Mortality
The Mother of All Pandemics
avian influenza, bird flu, influenza, pandemic, H5N1, H7N2
pppps - pay no attention to these thingies here.
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