Detection of high pathogenicity avian influenza virus in Antarctica during the International HPAI Australis Expedition 2024

The high pathogenicity avian influenza virus (HPAIV) subtype H5N1 (clade 2.3.4.4b) has caused a panzootic, with unprecedented massive outbreaks in wild mammals and birds. The rapid spread of the virus in South America raised concerns about HPAIV spreading to Antarctica. The virus was described to be introduced to Subantarctic Islands in October 2023 and suspected cases in Antarctica reported since November 2023. The first case of HPAIV in Antarctica was confirmed in February 2024 in dead skuas in Primavera Station (Antarctic Peninsula). With the purpose of monitoring HPAIV spread to Antarctica, an international expedition aboard the sailing vessel Australis was organized from 13th March to 3rd April 2024, looking for signs of the virus in seabirds and sea mammals throughout several locations in the South Shetland Islands, Trinity Peninsula and Northern Weddell Sea, where previous surveillance efforts had received notifications on potential mortality events or disease in wildlife. A molecular laboratory was set up on the vessel allowing to use state-of-the-art diagnostic methods for samples to be tested by RT-qPCR for presence of influenza A virus (IAV) (gene M) and the H5 subtype. HPAIV was confirmed by Oxford Nanopore sequencing of a region of the hemagglutinin gene encoding the multibasic cleavage site (MBCS), required for definitive HPAIV clade diagnostic. During the trip, we were able to detect and confirm the presence of HPAIV in skua carcasses at four landing sites (Beak Island, Hope Bay, Devil Island and Paulet Island) and in a dead snowy sheathbill at Heroina Island, representing the first report of HPAIV in this bird species.