Abstract:
Highly pathogenic avian influenza (HPAI) H5N1
expanded considerably during 2005 and early 2006 in both
avian host species and geographic distribution. Domestic
waterfowl and migratory birds are reservoirs, but lethality of
this subtype appeared to initially limit migrant effectiveness
as introductory hosts. This situation may have changed, as
HPAI H5N1 has recently expanded across Eurasia and into
Europe and Africa. Birds could introduce HPAI H5N1 to the
Western Hemisphere through migration, vagrancy, and
importation by people. Vagrants and migratory birds are
not likely interhemispheric introductory hosts; import of
infected domestic or pet birds is more probable. If reassort-ment
or mutation were to produce a virus adapted for rapid
transmission among humans, birds would be unlikely intro-ductory
hosts because of differences in viral transmission
mechanisms among major host groups (i.e., gastrointesti-nal
for birds, respiratory for humans). Another possible
result of reassortment would be a less lethal form of avian
influenza, more readily spread by birds.
