Crowder, J. C. | bioRxiv Science

bioRxiv2026

First detected incursions of avian influenza H5N1 clade 2.3.4.4b into mainland Australia from the Southern Ocean

High pathogenicity avian influenza H5N1 clade 2.3.4.4b has caused a panzootic of devastating impact to poultry and wildlife globally. The Australian continent and broader Oceania until recently remained the last major region without confirmed detections. Here we report the first H5N1 clade 2.3.4.4b detections from two live seabirds - a brown skua and a southern giant petrel - found on the south coast of Western Australia in June 2026. Virus genome sequencing showed that both viruses were most closely related to H5N1 viruses detected recently on sub-Antarctic islands in the Southern Indian Ocean. In time-calibrated phylogeographic analyses, both viruses sampled in Western Australia clustered with viruses from Heard Island, a sub-Antarctic external territory of Australia. Ancestral location reconstruction also identified Heard Island as the most probable source location, although unsampled intermediate locations cannot be excluded. The two Western Australian detections were estimated to be independent incursions from Heard Island, rather than local transmission on mainland Australia. There was no evidence of reassortment with endemic avian influenza viruses in Australia, and both virus sequences retained key avian-like genetic markers and lacked known substitutions for reduced antiviral susceptibility. These detections revealed a Southern Ocean pathway of recurrent H5N1 incursions into Australia, highlighting the risk of potential establishment on the mainland and the need for heightened surveillance and rapid, nationally-coordinated, virus genomic characterisation.

microbiology↗

bioRxiv2023

A transmission chain linking Mycobacterium ulcerans with Aedes notoscriptus mosquitoes, possums and human Buruli ulcer cases in southeastern Australia

In temperate southeastern Australia over the past two decades there has been a marked progressive increase in human cases of Buruli ulcer, an infection of subcutaneous tissue caused by Mycobacterium ulcerans. Native possums are the major local environmental reservoir of M. ulcerans as they not only develop Buruli lesions but they also shed M. ulcerans in their excreta. However the way humans acquire M. ulcerans from possums has not been determined. Previous case-control studies, insect field surveys and vector competence studies have suggested a role for mosquitoes in M. ulcerans transmission between possums and humans. To explore these links we conducted an extensive, 4-month structured mosquito field survey and four ad hoc field surveys across an area of 350km2 on the Mornington Peninsula, an area endemic for Buruli ulcer to the south of the major metropolitan city of Melbourne. We then compared spatial and temporal patterns of M. ulcerans-positive mosquito occurrence with M. ulcerans-positive possums (established by previous possum excreta surveys) and human Buruli ulcer cases across the region. We used metabarcoding to assess mosquito blood-feeding host preference and to reconstruct M. ulcerans genomes from positive mosquitoes to test epidemiological inferences. We collected 66,325 mosquitoes spanning 26 different species from 180 repeatedly sampled traps over a 4-month period. Culex molestus and Aedes notoscriptus were the dominant species (42% and 35% of trapped mosquitoes, respectively). PCR screening 25% of trapped mosquitoes revealed a significant association between M. ulcerans and Ae. notoscriptus (p<0.0001) with a maximum likelihood estimate (MLE) of 5.88 M. ulcerans positive mosquitoes per 1,000 tested. Using spatial scanning statistics, we also observed significant overlap between clusters of M. ulcerans-positive Ae. notoscriptus, M. ulcerans-positive possum excreta and human Buruli ulcer cases. Metabarcoding analyses of blood-fed Ae. notoscriptus showed individual mosquitoes had fed both on humans and native possums. Enrichment genome sequencing from PCR-positive mosquitoes confirmed shared M. ulcerans genome single-nucleotide polymorphism (SNP) profiles between mosquitoes, possum excreta and clinical human isolates within the same regions. These findings indicate that Ae. notoscriptus likely transmit M. ulcerans in southeastern Australia and highlight mosquito control as a plausible means to control the Buruli ulcer epidemic in our region.

microbiology↗