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HPAI Spread by Migratory Gulls


A study conducted in China confirmed that black-tailed gulls (Laris crassirostris) serve as reservoirs of H13 strain viruses.  Black-tailed gulls breed in Shandong Province in Eastern China but extend widely though Eastern and Southeast Asia.  Vagrant individuals have been recovered from Alaska, the Pacific coastline of North America and the Philippines.


A series of H13N2 and H13N8 isolates were obtained from black-tailed gulls and subjected to phylogenetic analysts.  It was determined that the neuraminidase segments were derived from the Eurasian lineage.  Both isolates possessed high nucleotide sequence identity conforming to subtypes isolated in Europe and North America. It was presumed that the H13 subtypes were reassortants between Eurasian and North American lineages.  Transfer of genetic material was estimated to have occurred from 2007 through 2014 and the complex process was apparently completed during mid-2015.  Although classified as low-pathogenicity strains, both H13N2 and H13N8 demonstrated markers associated with increased virulence and the potential for transmission to mammals.


A serologic survey among chickens in the area in which the gulls were sampled demonstrated titers against both H13N2 and H13N8 (8 percent and 30 percent respectively).  It was concluded that the H13 antibody response resulted from exposure to H13 viruses circulating among free-living birds.  Although the chicken farm from which samples were obtained was approximately 60 miles from the sampling site for gulls, the migratory pathway extended from the coastline over the farms.


This study demonstrated the significance of migratory birds other than waterfowl in the dissemination of avian influenza and the potential to infect commercial poultry.


*Yu, Z. et al Poultry Infection with Influenza Viruses of wild Bird Origin, China, 2016 Emerging Infectious Diseases 24: 1375-1377 (2018)