tracking bird flu: migratory birds & avian influenza spread, h5n1, h9n2, h7, h3

avian influenza bird migratory virus transmission h5n1 h7n9 h9n2 h5n8 outbreak poultry zoonotic epidemiology spread wildlife biosecurity contagion pandemic vaccination surveillance health control mutation containment immunization pathogen swallow warbler goose knot crane ecological quarantine virology symptoms treatment prevention rate history agriculture environmental habitat emergency sanitation conservation pathogenicity virulence h7 vaccine vaccination mutant mutation