Biology subjects

Clessin, A.

Publications and source records attributed to Clessin, A..

7 recordsLinked to original sources

bioRxiv2026

Large-scale exposure of southern seabirds to avian cholera Pasteurella multocida: scavengers as sentinels at different spatial scales

Seabird communities represent spatially structured social networks within which potential sentinels could inform us where multi-host pathogens could be present. Pasteurella multocida, the agent of avian cholera, is responsible for recurrent massive seabird mortality events on remote Amsterdam Island, Southern Indian Ocean, but little is known about its broad spatial occurrence. To explore its distribution and whether avian scavengers and predators could be used as sentinels, we screened 18 southern seabird species from 11 islands for antibodies against P. multocida (2634 plasma samples). We detected widespread but heterogeneous exposure among host populations. High seroprevalences were found in widely roaming predators and scavengers (giant petrels (Macronectes spp), and brown skua (Stercorarius antarcticus)), which could represent efficient sentinels at broad scales. Antibodies were also detected over a series of years in a non-migratory scavenger, the lesser sheathbill (Chionis minor) and an abundant penguin species, the king penguin (Aptenodytes patagonicus), suggesting that the bacterium was circulating locally at some sites. This broad scale serological screening of whole seabird host communities provides critical information to assess disease emergence risks in the context of global change.

ecology↗

bioRxiv2026

Dispersal, adaptation and persistence of H5N1 in the sub-Antarctic and Antarctica

High pathogenicity avian influenza virus (HPAIV) H5N1 reached the sub-Antarctic and Antarctica in 2023, subsequently spreading to remote locations within this region where it had devastating impacts on seal, penguin and albatross populations. The threat to marine wildlife over this broad area exemplifies the need to understand H5N1 long-distance dispersal and evolution. We obtained 104 novel viral genomic sequences from samples that we collected at South Georgia, Kerguelen, Crozet, Prince Edward, Falklands/Malvinas Islands and the Antarctic Peninsula in a region spanning 8,000 kilometers. Using recent phylogeographic modeling advances we show that H5N1 spread encompassed numerous transmission events between distant locations, accumulating mammalian-adaptive mutations in the process. Seals are the most affected species, but we reveal that the long-distance eastward virus dispersal better aligns with the long-distance movements of large petrels and albatrosses. The risk of H5N1 endemisation, dispersal to other locations and ongoing evolution are highly concerning.

microbiology↗

bioRxiv2026

High pathogenicity avian influenza virus H5N1 clade 2.3.4.4b in Antarctica: Multiple Introductions and the First Confirmed Infection of Ice-Dependent Seals

Highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b has expanded rapidly across the Southern Ocean since 2023, causing extensive mortality in sub-Antarctic wildlife. Yet its penetration into Antarctica and impacts on ice-dependent species remain poorly resolved primarily due to surveillance constraints. We report the first confirmed H5N1 infection in an Antarctic ice-dependent seal (crabeater seal; Lobodon carcinophaga) and document mortality of crabeater seals across the northern Weddell Sea during November-December 2024. Combining genomic, serological and observational data across nine species, we detected H5N1 RNA in a crabeater seal and a kelp gull (Larus dominicanus), and recovered complete HA, NA and M2 gene sequences from both. Phylogenetic analyses allowed us to identify at least two independent introductions of HPAI H5N1 clade 2.3.4.4b into the northern Antarctic Peninsula region. Serology provided strong evidence of prior exposure in scavenging birds, but no detectable H5 immunity in penguins or pinnipeds. Together, the results demonstrate ongoing novel viral incursions into Antarctica, likely facilitated by at-sea processes e.g. animal interactions on ice floes, that remain invisible to land-based surveillance. These findings highlight the vulnerability of ice-dependent pinnipeds to HPAI H5N1 clade 2.3.4.4b and the urgent need for expanded integrated Antarctic monitoring frameworks that pair serology, opportunistic carcass sampling and genomic sequencing.

ecology↗

bioRxiv2025

Mass mortality events in the sub-Antarctic Indian Ocean caused by long-distance circumpolar spread of highly pathogenic avian influenza H5N1 clade 2.3.4.4b

Since 2020, the outbreak of highly pathogenic avian influenza (HPAI) virus clade 2.3.4.4b has turned into the largest documented panzootic to date, reaching the sub-Antarctic region and Antarctica via the tip of South America in 2023. Here, we describe its recent arrival into the Indian Ocean sub-Antarctic archipelagos of Crozet and Kerguelen, where we first detected the virus in October 2024 in dead southern elephant seals, king penguins, gentoo penguins, brown skuas and kelp gulls. While the panzootic is ongoing, it has already caused unprecedented and alarming mortalities of southern elephant seals. We collected brain swabs from various seal and bird carcasses, subsequently isolated the virus and obtained 25 novel HPAI H5N1 clade 2.3.4.4b sequences. Our phylogenetic and phylogeographic analyses show that there have been independent introductions of the virus to Crozet and Kerguelen, from the distant South Georgia Islands in the Southern Atlantic, and not from the more nearby coasts of South Africa. Our results point to a year-long gap in genomic surveillance in the south polar region, obscuring how HPAI H5N1 clade 2.3.4.4b is spreading in the sub-Antarctic and illustrating the difficulties in tracking pathogen dispersal in the region. Locally, our phylogenetic analyses show that the virus is transmitted between different species. Moreover, our serological analyses show that some southern elephant seal pups had mounted an anti-H5 antibody response. With the spread to Crozet and Kerguelen, HPAI H5N1 2.3.4.4b is moving ever closer to Australia and New Zealand, which currently remain free from infections with this strain, and represents a major threat to the sub-Antarctic wildlife. Our results provide key elements to enable stakeholders to anticipate the arrival and spread of the virus in remote areas of critical wildlife conservation concerns.

microbiology↗

bioRxiv2024

The evolution of GC-biased gene conversion by means of natural selection

GC-biased gene conversion (gBGC) is a recombination-associated evolutionary process that biases the segregation ratio of AT:GC polymorphisms in the gametes of heterozygotes, in favour of GC alleles. This process is the major determinant of variation in base composition across the human genome and can be the cause of a substantial burden of GC deleterious alleles. While the importance of GC-biased gene conversion in molecular evolution is increasingly recognised, the reasons for its existence and its variation between species remain largely unknown. Using simulations and semi-analytical approximations, we investigated the evolution of gBGC as a quantitative trait evolving by mutation, drift and natural selection. We show that in a finite population where most mutations are deleterious, gBGC is under weak stabilising selection around a positive value that mainly depends on the intensity of the mutation bias and on the intensity of selective constraints exerted on the genome. Importantly, the levels of gBGC that evolve by natural selection do not minimize the load in the population, and even increase it substantially in regions of high recombination rate. Therefore, despite reducing the populations fitness, levels of gBGC that are currently observed in humans could in fact have been (weakly) positively selected.

evolutionary biology↗

bioRxiv2023

No evidence for highly pathogenic avian influenza virus H5N1 (clade 2.3.4.4b) in the Antarctic region during the austral summer 2022/23

The current highly pathogenic avian influenza H5N1 panzootic has substantial impacts on wild birds and marine mammals. Although major outbreaks occurred in South America, incursion to Antarctica emerged late in the breeding season of 2023/2024 and was confined the wider region of the Antarctic Peninsula. To infer potential underlying processes, we compiled H5N1 surveillance from Antarctica and Sub-Antarctic Islands prior to the first confirmed cases.

microbiology↗

bioRxiv2022

Genomic characterisation of a novel species of Erysipelothrix associated with mortalities among endangered seabirds

Infectious diseases threaten endangered species, particularly in small isolated populations. Seabird populations on the remote Amsterdam Island in the Indian Ocean have been in decline for the past three decades, with avian cholera caused by Pasteurella multocida proposed as the primary driver. However, Erysipelothrix spp. has also been sporadically detected from albatrosses on Amsterdam Island and may be contributing to some of the observed mortality. In this study, we genomically characterised 16 Erysipelothrix spp. isolates obtained from three Indian yellow-nosed albatross chick carcasses in 2019. Two isolates were sequenced using both Illumina short-read and MinION long-read approaches, which - following hybrid assembly - resulted in closed circular genomes. Mapping of Illumina reads from the remaining isolates to one of these new reference genomes revealed that all 16 isolates were closely related, with a maximum of 13 nucleotide differences distinguishing any pair of isolates. The nucleotide diversity of isolates obtained from the same or different carcasses was similar, suggesting all three chicks were likely infected from a common source. These genomes were compared with a global collection of genomes from E. rhusiopathiae and other species from the same genus. The isolates from albatrosses were phylogenetically distinct, sharing a most recent common ancestor with E. rhusiopathiae. Based on phylogenomic analysis and standard thresholds for average nucleotide identity and digital DNA-DNA hybridisation, these isolates represent a novel Erysipelothrix species, for which we propose the name Erysipelothrix amsterdamensis sp. nov. The type strain is E. amsterdamensis A18Y020dT. The implications of this bacterium for albatross conservation will require further study.

genomics↗