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This is Science Friday. I'm Flora Lichten.

This week, according to the USDA and the World Organization for Animal Health,

a different strain of bird flu has turned up in the U.S.

H5N9.

It caused a November outbreak of a highly pathogenic avian influenza on a California duck farm.

The dominant bird flu strain currently circulating, H5N1, has led to massive culling of bird flocks worldwide and is now affecting

dairy cattle. The U.S. reported its first human death from H5N1 bird flu earlier this month.

Joining me now to talk about this and other stories from the week in science is Cy Fry's Charles

Berkwist. Hi, Charles. Hey, Flora. So a new kind of bird flu, huh? Yeah, I mean,

this gets a little bit weedy, but when we talk about different kinds of flu, there's like the

super big level. First, what type of influenza, A, B, C, D? A and B are the kinds of flu you think

about when we talk about people getting affected with seasonal flu.

C is a kind that can affect people, but it's usually a mild.

D is mainly a cattle thing.

Okay.

All of the viruses we're talking about here with the bird flu are flu A.

But then you get into these H and N designations.

That talks about what specific form of two proteins called

hemaglutinin and neuraminidase are on the surface of the virus. Then there can be even

like finer distinctions called clades, subclades, but what we're talking about here is

influenza A, H5N9, as opposed to influenza A, H5, N1, which is what's been mainly affecting bird flocks.

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