Long-tailed ducks gather in Beaufort Sea Lagoons to molt during the summer months and the high density of flightless birds increases their susceptibility to adverse weather, anthropogenic activity, predation and disease.1 Viruses have not been known to cause mortality in long-tailed ducks until a die-off occurred in 2000 80 km east of Prudhoe Bay.2 Adenovirus isolates were obtained from carcasses and live carrier long-tailed ducks at the mortality site, and from live ducks at a control site. A previous study on an isolate from a carcass evaluated its pathogenicity and confirmed its virulence through challenge experiments with long-tailed ducks.2 This project had four objectives: 1) genetically compare the adenovirus isolates from the mortality and control sites using PCR; 2) sequence the PCR-amplified portion of the hexon gene; 3) conduct cross-neutralization assays on the different genotypes; and 4) phylogenetically analyze the hexon sequences. Several adenovirus isolates representing the different genotypes were tested in cross-neutralization assays with group I or II antisera, but no neutralization was observed. Twenty-one isolates were grown in Muscovy duck embryo fibroblasts and successfully amplified with PCR using primer sets developed in our laboratory that target the hexon gene. Nineteen isolates were sequenced, and three genotypes were identified in the long-tailed duck adenovirus sequences. The hexon sequences of 11 of the isolates were highly similar to one another and comprised the first genotype, which phylogenetic analysis using the maximum likelihood method suggested were most related to the goose adenovirus. Included within the primary genotype was the isolate that was confirmed to be virulent in challenge studies. The two isolates from live ducks at the control site were not related to the primary group of isolates. The other two genotypes each contained four isolates that were highly related to each other, but not to any other known adenovirus. The source of the adenovirus infection in long-tailed ducks is unknown, but phylogenetic analysis placed all of the isolates in the Aviadenovirus genus. This genus has only been known to infect bird species; therefore, an avian source is likely. Research into the pathogenesis of the novel genotypes that are unrelated to other known adenoviruses will lead to a better understanding of how they cause disease and what birds may be at risk. Climate change and increased anthropogenic activity in the Arctic may increase stress on sea ducks in the region and heighten their susceptibility to disease. Novel pathogens, such as the long-tailed duck adenovirus, have the potential to cause high mortality in naïve populations.
We would like to thank Dr. Lee Skerratt for the work he did developing primers. This project was funded by the U.S. Fish and Wildlife Service.
* Presenting author
+ Student presenter
1. Flint PL, Reed JA, Franson JC, Hollmén TE, Grand JB, Howell MD, Lanctot RB, Lacroix DL, Dau CP. Monitoring Beaufort Sea waterfowl and marine birds. U.S. Geological Survey, Alaska Science Center, Anchorage, Alaska OCS Study MMS 2003-037. 2003.
2. Hollmén TE, Franson JC, Flint PL, Grand JB, Lanctot RB, Docherty DE, Wilson HM. An adenovirus linked to mortality and disease in long-tailed ducks (Clangula hyemalis) in Alaska. Avian Dis. 2003;47:1434–1440.