Prevalence of Influenza A viruses in wild migratory birds in Alaska: patterns of variation in detection at a crossroads of intercontinental flyways.
BACKGROUND
The global spread of the highly pathogenic avian influenza H5N1 virus has stimulated interest in a better understanding of the mechanisms of H5N1 dispersal, including the potential role of migratory birds as carriers. Although wild birds have been found dead during H5N1 outbreaks, evidence suggests that others have survived natural infections, and recent studies have shown several species of ducks capable of surviving experimental inoculations of H5N1 and shedding virus. To investigate the possibility of migratory birds as a means of H5N1 dispersal into North America, we monitored for the virus in a surveillance program based on the risk that wild birds may carry the virus from Asia.


RESULTS
Of 16,797 birds sampled in Alaska between May 2006 and March 2007, low pathogenic avian influenza viruses were detected in 1.7% by rRT-PCR but no highly pathogenic viruses were found. Our data suggest that prevalence varied among sampling locations, species (highest in waterfowl, lowest in passerines), ages (juveniles higher than adults), sexes (males higher than females), date (highest in autumn), and analytical technique (rRT-PCR prevalence = 1.7%; virus isolation prevalence = 1.5%).


CONCLUSIONS
The prevalence of low pathogenic avian influenza viruses isolated from wild birds depends on biological, temporal, and geographical factors, as well as testing methods. Future studies should control for, or sample across, these sources of variation to allow direct comparison of prevalence rates.
Ip
Hon S
HS
US Geological Survey, National Wildlife Health Center, Madison, Wisconsin, USA. hip@usgs.gov
Flint
Paul L
PL
Franson
J Christian
JC
Dusek
Robert J
RJ
Derksen
Dirk V
DV
Gill
Robert E
RE
Ely
Craig R
CR
Pearce
John M
JM
Lanctot
Richard B
RB
Matsuoka
Steven M
SM
Irons
David B
DB
Fischer
Julian B
JB
Oates
Russell M
RM
Petersen
Margaret R
MR
Fondell
Thomas F
TF
Rocque
Deborah A
DA
Pedersen
Janice C
JC
Rothe
Thomas C
TC
D000367:Age Factors; D000413:Alaska / Q000453:epidemiology; D025041:Animal Migration; D000818:Animals; D001717:Birds / Q000821:virology*; D005260:Female; D053124:Influenza A Virus, H5N1 Subtype / Q000145:classification / Q000302:isolation & purification*; D005585:Influenza in Birds / Q000453:epidemiology*; D008297:Male; D015995:Prevalence; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012621:Seasons; D012737:Sex Factors