Every time bird flu comes up in the news, it seems to have originated in east Asia, and we hear about (for example) Chinese authorities slaughtering chickens by the thousands and spraying disinfectants all over chicken markets.
Is there something about this part of the world that is conducive to the mutation of bird flu into a human-compatible form? Or is there a media bias in place so that when this happens in South America or Africa, I just never hear about it? Or do I have my own bias?
The explanation I heard is that SE Asia is the place where a lot of people raise pigs, and they live on migratory bird paths. Plus, people live in close proximity to their livestock, with less-than-ideal sanitation especially in the rural areas.
Pigs have a remarkably similar susceptibility to disease as humans - we are more likely to catch pig diseases than cows, or goats, etc.
The birds from SE asia migrate all over, from Siberia down to the Indonesian tropics picking up all sorts of bacteria. These birds passing through leave their calling cards in the wet muck of pigpens where it mixes with bacteria that like pigs. Bacteria in close proximity have a habit of exchanging small bits of their DNA, IIRC. The pigs can pick this up and pass it to humans. If it can be spread by birds too, bonus; SE Asia also has a lot of chickens, also raised in proximity in less than sanitary surroundings. The tropical wet weather is ideal for incubating bacteria.
All in all, a perfect storm of a massive bacteria-grwoing petrie dish with birds, hogs, and humans all tossed in to find the right bacteria before it disappears…
The explanation above is very similar to the one I learned in virology. That is, that a common farming practice in SE Asia is to keep chickens above the pig pens, so chicken shit falls in with the pigs and exposes them to avian strains. Later, the pig/chicken shit is thrown into the rice paddies where the ducks get exposed to it.
In both explanations, the close proximity of fowl, swine, humans, and waterfowl creates ideal opportunities for influenza to swap bits.
I’m sure you meant viruses, since the flu is a viral disease, although you are correct about bacteria swapping DNA (viruses can do this too), which can lead to other nasties.
This is a particular problem for flu, because influenza, unlike most viruses, has its genome broken up into multiple strands of RNA, sort of like chromosomes. So instead of going through the relatively tedious and difficult process of recombination to swap genetic information around, they can simply reshuffle different chromosomes around when an individual organism is infected with more than one strain at once. This is another reason why it’s so easy for new strains to arise.