Evolutionarily, why should wounds itch?

[athon]

When you say "we" I don't think you mean Africans. They're the folk who've had an arms-race with parasites for millions of years. An unintended consequence for humans who had to leave Africa was a sharp drop in their parasite-load. Population soared. Animals were domesticated. And their parasites became our new diseases.

Publicity notwithstanding, bird-flu is a lot scarier than Aids. Aids is old-school, influenza is in the modern arms-race.

I'm not sure what you mean here. In terms of evolution, human physiology is pretty much the same world over. We (all humans) developed in an African climate, although for the past 10,000 odd years civilisation has brought a range of new pathogens, for the majority of our history we were nomads in a narrow range of African environments. So this 'arms-race' (as you nicely put it) is relevant to all physiologically modern humans. There is are slight evolutionary trends in various global populations towards different pathogens, however our basic immune systems are the same. While many climates have different (and often fewer) parasite loads, we have not lost the immunological features which accounted for evolving alongside them.

Influenza is indeed a scary pathogen, simply because it is so novel to human physiology. Funny how pathology works.

Athon