I don't like to speculate much because I'm hardly qualified and there are doctors who have seen what goes on and seem to say different, but what I
think is that this is a very aggressive strain of influenza. From what I've seen, it seems to spread much the same way and has some of the same symptoms.
People forget how dangerous the flu can be, I think. Look up the
1918 flu pandemic .. that killed many millions of people quickly and often caused massive bleeding in the lungs which I guess perhaps could have blackened them like they see in the Ukraine.