High pathogenicity avian influenza (H5N1) in Northern Gannets: Global spread, clinical signs, and demographic consequences

Abstract

During 2021-22 High Pathogenicity Avian Influenza (HPAI) killed thousands of wild birds across Europe and North America, suggesting a change in infection dynamics and a shift to new hosts, including seabirds. Northern Gannets (Morus bassanus) appeared especially severely impacted, but limited understanding of how the virus spread across the metapopulation, or the demographic consequences of mass mortality limit our understanding of its severity. Accordingly, we collate information on HPAIV outbreaks across most North Atlantic gannet colonies and for the largest colony (Bass Rock, UK), provide impacts on population size, breeding success, adult survival, and preliminary results on serology. Unusually high numbers of dead gannets were first noted in Iceland during April 2022. Outbreaks in May occurred in many Scottish colonies, followed by colonies in Canada, Germany and Norway. By the end of June, outbreaks had occurred in five Canadian colonies and in the Channel Islands. Outbreaks in 12 UK and Ireland colonies appeared to follow a clockwise pattern with the last infected colonies recorded in late August/September. Unusually high mortality was recorded at 40 colonies (75% of global total colonies). Dead birds testing positive for HPAIV H5N1 were associated with 58% of these colonies. At Bass Rock, the number of occupied sites decreased by at least 71%, breeding success declined by ~66% compared to the long-term UK mean and adult survival between 2021 and 2022 was 42% lower than the preceding 10-year average. Serological investigation detected antibodies specific to H5 in apparently healthy birds indicating that some gannets recover from HPAIV infection. Further, most of these recovered birds had black irises, suggestive of a phenotypic indicator of previous infection. Untangling the impacts of HPAIV infection from other key pressures faced by seabirds is key to establishing effective conservation strategies for threatened seabird populations, HPAIV being a novel and pandemic threat.

Weathering the Storm of High Pathogenicity Avian Influenza in Waterbirds

“…In addition to the adult birds, within colonies, almost all chicks died (Knief et al2023). Northern Gannets (Morus bassanus)were similarly heavily affected in the Atlantic, with unusually high mortality at colonies, including at Bass Rock in Scotland where the number of occupied nests decreased by 71%(Lane et al 2023). The total number of dead…”

HPAIV outbreak triggers enhanced colony connectivity in a seabird metapopulation

“…We deployed 18 g nano x GPS-GSM devices (Pathtrack Ltd.) with TESA tape to the tail of ten gannets from ve breeding pairs in April 2022, before egg-laying, and con rmed that each pair incubated an egg in late May 2022. On the 4 June 2022, the rst clinical symptoms of HPAIV were observed in gannets on the Bass Rock and an outbreak of clade 3.2.4.4b HPAIV H5N1 was con rmed shortly thereafter 4 . Over the following month, the outbreak reduced the colony size by 72 % and suppressed adult apparent survival to 0.455 % 4 .…”

“…On the 4 June 2022, the rst clinical symptoms of HPAIV were observed in gannets on the Bass Rock and an outbreak of clade 3.2.4.4b HPAIV H5N1 was con rmed shortly thereafter 4 . Over the following month, the outbreak reduced the colony size by 72 % and suppressed adult apparent survival to 0.455 % 4 . All study birds had lost their egg/chick by 15 June 2022, six birds survived the outbreak and one bird was found dead (Figure 1D, Table S1).…”

“…The study animals were highly likely exposed to the virus since they nested in an area where in-situ observations showed severe mortality of adult breeders 4 . The duration of viral shedding for HPAIV for seabirds is unknown, but data from six experimentally infected wild duck species suggests that live virus can be shed from 1-2 days after inoculation, for periods between 5 and 14 days 32 , hence the onset and duration of long-distance movements described here fall well within such a timeframe.…”

“…If the pattern scales up to the colony level, the outbreak of HPAIV may selfpropagate transmission by altering gannet movement and aggravating the connectivity between different gannet colonies as well as causing incursions into novel habitat types with susceptible animal communities. Such super-spreading 33 , even by a small number of individuals, might explain the rapid spread through the gannet colony networks in the West and East Atlantic 4 .…”