Biology subjects

Mollett, B.

Publications and source records attributed to Mollett, B..

7 recordsLinked to original sources

bioRxiv2026

The mammalian-adaptive PB2-E627K substitution preserves viral fitness of clade 2.3.4.4b H5N1 HPAIV in birds.

Since emerging in 2020, clade 2.3.4.4b H5N1 high pathogenicity avian influenza virus (HPAIV) has disseminated globally, causing substantial infection and mortality in wild birds and poultry. Additionally, numerous spill-over events into mammals have occurred, including mass mortalities and sporadic human infections. Such events can drive the acquisition of mammalian-adaptive mutations, which further increase the risk to humans; the most well characterised mutation is the glutamate to lysine change at amino acid position 627 in the polymerase basic 2 protein (PB2-627K). Across avian influenza viruses, PB2-627K enhances polymerase activity and replication in mammalian cells, increasing zoonotic and pandemic potential. However, bioinformatic analyses indicate that PB2-627K remains rare among clade 2.3.4.4b H5N1 viruses circulating in avian populations. Here, we investigated the impact of PB2-627K on viral fitness in avian hosts to assess the potential for mammalian-adapted viruses to re-establish in birds, mimicking infection of avian species following scavenging on mammalian species where PB2-627K has already emerged. Using a representative H5N1 virus (European genotype AB), PB2-627K increased polymerase activity and replication in human cells without compromising replication in avian cells. A mammalian-derived PB2-627K H5N1 isolate from a fox exhibited comparable replication kinetics and transmission efficiency in chickens and ducks to a closely related PB2-627E virus. Notably, PB2-627K remained genetically stable at consensus level following infection and transmission in both avian hosts. These findings demonstrate that mammalian-adaptive mutations acquired during spill-over can be maintained in avian populations, potentially elevating zoonotic risk and underscoring the importance of surveillance for such mutations in birds.

microbiology↗

bioRxiv2026

Genetic diversity and phylogeography of swine influenza A virus in 2013-2022 in Europe using a harmonized genotyping nomenclature

Swine Influenza A virus (swIAV) poses constant health threat for both humans and animals. This study comprehensively analysed the genetic diversity and evolution of European swIAVs from 2013 to 2022. To address existing classification gaps, an easily accessible full-genome genotyping tool based on Nextclade was developed alongside a global nomenclature system. Application of this tool to European sequence data revealed unprecedented genetic diversity, successfully identifying 150 swIAV genotypes mixing segments of both swine and human origin. Bayesian phylogeographic models, combined with economic data, identified that the trade of live weaner pigs for fattening drove the transboundary spread of swIAVs across Europe. The study detected repeated human-to-swine reverse-zoonotic events across multiple European countries. These findings clearly highlight the role of commercial pig movements in viral dissemination and emphasize the critical importance of harmonized genomic surveillance to monitor swIAV viral evolution to inform global pre-pandemic preparedness strategies.

microbiology↗

bioRxiv2025

Detection of clade 2.3.4.4b H5N1 high pathogenicity avian influenza virus in a sheep in Great Britain, 2025

Clade 2.3.4.4b H5N1 high pathogenicity avian influenza virus (HPAIV) continues to pose a significant global threat, affecting wild and domestic avian populations, and mammalian species. In early 2024, H5N1 HPAIV was detected in dairy cattle in the United States of America, where it has continued to circulate, with sporadic detections also reported in other ruminant species. The detection of high viral loads in milk from infected cattle, has resulted in several human infections, underscoring the zoonotic potential of these viruses. In response, several countries have intensified surveillance in non-avian species to evaluate the potential for undetected viral circulation in captive mammals. In Great Britain, bulk milk tank testing of cattle and targeted surveillance of captive mammalian species on an infected premises is undertaken in accordance with the outcome of a rapid risk assessment undertaken to determine the epidemiological links between the poultry and captive mammals. A result of this testing was the first recorded detection of clade 2.3.4.4b H5N1 HPAIV in a sheep in March 2025, identified on an infected poultry premises in Great Britain. An initial seropositive result in a single ewe triggered further investigation, confirming serological positivity across repeated sampling and the presence of viral RNA in milk samples. This detection was confined to a single animal and was likely attributable to proximity to infected poultry and a presumed heavily contaminated environment. The implications of this ruminant detection are discussed in the context of interspecies transmission and surveillance strategies.

microbiology↗

bioRxiv2024

Rapid mortality in captive bush dogs (Speothos venaticus) caused by influenza A of avian origin (H5N1) at a wildlife collection in the United Kingdom

Europe has suffered unprecedented epizootics of high pathogenicity avian influenza (HPAI) clade 2.3.4.4b H5N1 since Autumn 2021. As well as impacting upon commercial and wild avian species, the virus has also infected mammalian species more than ever observed previously. Mammalian species involved in spill over events have primarily been scavenging terrestrial carnivores and farmed mammalian species although marine mammals have also been affected. Alongside reports of detections in mammalian species found dead through different surveillance schemes, several mass mortality events have been reported in farmed and wild animals. During November 2022, an unusual mortality event was reported in captive bush dogs (Speothos venaticus) with clade 2.3.4.4b H5N1 HPAIV of avian origin being the causative agent. The event involved an enclosure of fifteen bush dogs, ten of which succumbed during a nine-day period with some dogs exhibiting neurological disease. Ingestion of infected meat is proposed as the most likely infection route.

microbiology↗

bioRxiv2023

Detection and spread of high pathogenicity avian influenza virus H5N1 in the Antarctic Region

Until recent events, the Antarctic was the only major geographical region in which high pathogenicity avian influenza virus (HPAIV) had never previously been detected. The current panzootic of H5N1 HPAIV has decimated wild bird populations across Europe, North America, and South America. Here we report on the detection of clade 2.3.4.4b H5N1 HPAIV in the Antarctic and sub-Antarctic regions of South Georgia and the Falkland Islands, respectively. We initially detected H5N1 HPAIV in samples collected from brown skuas at Bird Island, South Georgia on 8th October 2023. Since this detection, mortalities were observed in brown skuas, kelp gulls, South Georgia shag, Antarctic tern, elephant seals and fur seals at multiple sites across South Georgia. Subsequent testing confirmed H5N1 HPAIV across several sampling locations in multiple avian species and two seal species. Simultaneously, we also confirmed H5N1 HPAIV in southern fulmar and black-browed albatross in the Falkland Islands. Genetic assessment of the virus indicates spread from South America, likely through movement of migratory birds. Critically, genetic assessment of sequences from mammalian species demonstrates no increased risk to human populations. Here we describe the detection, species impact and genetic composition of the virus and propose both introductory routes and potential long-term impact on avian and mammalian species across the Antarctic region. We also speculate on the threat to specific populations following recent reports in the area.

microbiology↗

bioRxiv2022

The origin of internal genes contributes to the replication and transmission fitness of H7N9 avian influenza virus

H9N2 avian influenza viruses (AIVs) have donated internal gene segments during the emergence of zoonotic AIVs, including H7N9. We used reverse genetics to generate three reassortant viruses (2:6 H7N9) which contained the Haemagglutinin and Neuraminidase from Anhui/13 (H7N9) and the six internal gene segments from H9N2 AIVs of G1-like or BJ94-like lineages enzootic in different geographic regions in Asia. Infection of chickens with the 2:6 H7N9 containing internal gene segments from G1-like H9N2 conferred attenuation in vivo, with lower shedding and reduced transmission to contact chickens. However, possession of BJ94-like H9N2 internal gene segments resulted in more rapid transmission and significantly elevated cloacal shedding compared to the parental Anhui/13 H7N9. In vitro analysis also showed that the 2:6 H7N9 having BJ94-like internal genes had significantly increased replication compared to the Anhui/13 H7N9 in chicken cells. In vivo co-infection experiments followed, where chickens were co-infected with pairs of Anhui/13 H7N9 and one of each of the three 2:6 H7N9 reassortants. During ensuing transmission events, the Anhui/13 H7N9 virus outcompeted 2:6 H7N9 with internal gene segments of BJ94-like or G1-like H9N2 viruses. Co-infection did lead to the emergence of novel reassortant genotypes that were transmitted to contact chickens. Some of the reassortant viruses had a greater replication in chicken and human cells compared to the progenitors. We demonstrated that the internal gene cassette determines the transmission fitness of H7N9 viruses in chickens and the reassortment events can generate novel H7N9 genotypes with increased virulence in chickens and enhanced zoonotic potential. ImportanceH9N2 avian influenza viruses (AIVs) are enzootic in poultry in different geographical regions. The internal genes of these viruses can be exchanged with other zoonotic AIVs, most notably the China-origin H7N9 that can give rise to new virus genotypes with increased veterinary, economic and public health threats to both poultry and humans. We investigated the propensity of the internal genes of H9N2 viruses (G1 or BJ94) in the generation of novel reassortant H7N9 AIVs. We observed that the internal genes of H7N9 which were derivative of BJ94-like H9N2 virus have a fitness advantage compared to those from the G1-like H9N2 viruses for efficient transmission among chickens. We also observed the generation of novel reassortant viruses during chicken transmission which infected and replicated efficiently in human cells. Therefore, such emergent reassortant genotypes may pose an elevated zoonotic threat.

microbiology↗

bioRxiv2021

Co-infection of chickens with H9N2 and H7N9 avian influenza viruses leads to emergence of reassortant H9N9 virus with increased fitness for poultry and enhanced zoonotic potential

An H7N9 low pathogenicity avian influenza virus (LPAIV) emerged through genetic reassortment between H9N2 and other LPAIVs circulating in birds in China. This virus causes inapparent clinical disease in chickens, but zoonotic transmission results in severe and fatal disease in humans. We evaluated the consequences of reassortment between the H7N9 and the contemporary H9N2 viruses of G1 lineage that are enzootic in poultry across the Indian sub-continent and the Middle East. Co-infection of chickens with these viruses resulted in emergence of novel reassortant H9N9 viruses carrying genes derived from both H9N2 and H7N9 viruses. These reassortant H9N9 viruses showed significantly increased replication fitness, enhanced pathogenicity in chicken embryos and the potential to transmit via contact among ferrets. Our study highlights that the co-circulation of H7N9 and H9N2 viruses could represent a threat for the generation of novel reassortant viruses with greater virulence in poultry and an increased zoonotic potential. O_FIG O_LINKSMALLFIG WIDTH=197 HEIGHT=200 SRC="FIGDIR/small/438444v1_ufig1.gif" ALT="Figure 1"> View larger version (96K): org.highwire.dtl.DTLVardef@1f425cborg.highwire.dtl.DTLVardef@1dd3ba2org.highwire.dtl.DTLVardef@1762348org.highwire.dtl.DTLVardef@1064cb7_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG In BriefH9N2 viruses have a high propensity to reassort with other avian influenza viruses. We found that co-infection of chickens with H9N2 and H7N9 led to the emergence of reassortant viruses including the H9N9 subtype. Some reassortant H9N9 viruses exhibited increased replication fitness, increased pathogenicity in the chicken embryo, greater avidity for human and avian cell receptors, lower pH fusion and contact-transmission to ferrets. This study demonstrated the ability of viruses that already exist in nature to exchange genetic material, highlighting the potential emergence of viruses from these subtypes with increased zoonotic potential. There are nine H9 influenza A subtypes carrying different neuraminidase (NA) genes, including H9N9 viruses, while they are not common they do exist in nature as wildtypes (CDC). HighlightsO_LICo-infection of chickens with H7N9 and H9N2 led to emergence of reassortant H9N9 viruses C_LIO_LIReassortant H9N9 viruses had an increased replication rate in avian and human cells C_LIO_LIReassortant H9N9 viruses had a lower pH fusion and significantly higher receptor binding to 2,3 sialoglycans C_LIO_LIReassortant H9N9 replicated in ferrets at similar levels compared to H7N9 and transmitted via direct contact C_LIO_LIFerrets exposed to reassortant H9N9 by aerosol contact were also found to be seropositive C_LIO_LIExperimental simulation of events that may occur naturally with circulating viruses has demonstrated the risk of emergence of viruses with increased zoonotic potential. C_LI

microbiology↗