- Volume 106, Issue 7, 2025

Flaviviridae is a family of viruses that are mainly transmitted by mosquito vectors of the genus Aedes, which cause febrile illnesses and, in severe cases, haemorrhagic or neurodegenerative conditions. Over time, these viruses have been reported as emerging pathogens, leading to epidemic outbreaks in various regions worldwide. Additionally, climate change has facilitated the migration of these vectors to regions where they were not previously found. Unfortunately, there are currently no effective treatments or vaccines to prevent or combat Orthoflavivirus infections. Consequently, a deeper understanding of the viral biology and the human host immune response is crucial for advancing the development of therapeutic targets. Amongst the molecules involved in the innate immune response to viral infections are antimicrobial peptides (AMPs), which have been studied for decades. However, their role in Orthoflavivirus infections remains poorly understood. Several researchers have proposed the stimulation or exogenous administration of AMPs during various viral infections, highlighting these molecules as potential innovative therapeutic targets. This study compiles current knowledge on AMPs with a specific focus on Orthoflavivirus infections, emphasizing the importance of these promising therapeutic approaches.

Coronaviruses are abundant and diverse RNA viruses with broad vertebrate host ranges. These viruses include agents of human seasonal respiratory illness, such as human coronaviruses OC43 and HKU1; important pathogens of livestock and domestic animals such as swine acute diarrhoea syndrome coronavirus and feline coronavirus; and human pathogens of epidemic potential such as SARS-CoV, MERS-CoV and SARS-CoV-2. Most coronavirus surveillance has been conducted in bat species. However, small terrestrial mammals such as rodents and eulipotyphlans are important hosts of coronaviruses as well. Although fewer studies of rodent and eulipotyphlan coronaviruses exist compared to those of bats, notable diversity of coronaviruses has been reported in the former. No literature synthesis for this area of research has been completed despite (a) growing evidence for a small mammal origin of certain human coronaviruses and (b) global abundance of small mammal species. In this review, we present an overview of the current state of coronavirus research in wild terrestrial small mammals. We conducted a literature search for studies that investigated coronaviruses infecting rodent and eulipotyphlan hosts, which returned 63 studies published up to and including 2024. We describe trends in coronavirus diversity and surveillance for these studies. To further the examination of the interrelatedness of these viruses, we conducted a phylogenetic analysis of coronavirus whole genomes recovered from rodent and eulipotyphlan hosts. We discuss important facets of terrestrial small mammal coronaviruses, including evolutionary aspects and zoonotic spillover risk. Lastly, we present important recommendations and considerations for further surveillance and viral characterization efforts in this field.

RNA viruses are ubiquitous in the environment and are important pathogens of humans, animals and plants. In 2024, the International Committee on Taxonomy of Viruses Animal dsRNA and ssRNA(−) Viruses Subcommittee submitted 18 taxonomic proposals for consideration. These proposals expanded the known virosphere by classifying 9 new genera and 88 species for newly detected virus genomes. Of note, newly established species expand the large family of Rhabdoviridae to 580 species. A new species in the family Arenaviridae includes a virus detected in Antarctic fish with a unique split nucleoprotein ORF. Additionally, four new species were established for historically isolated viruses with previously unsequenced genomes. Furthermore, three species were abolished due to incomplete genome sequence information, and one family was moved from being unassigned in the phylum Negarnaviricota into a subphylum and order. Herein, we summarize the 18 ratified taxonomic proposals and the general features of the current taxonomy, thereby supporting public and animal health responses.

The International Committee on Taxonomy of Viruses (ICTV) holds a ratification vote annually after review of newly proposed taxa by ICTV Study Groups and members of the virology community. In March 2025, the vote outcome of the 11 proposals within the mandate of the Animal DNA Viruses and Retroviruses Subcommittee was made public. Here, we provide a summary of the newly accepted proposals. These include reorganization of taxa in the realm Varidnaviria, classification of the ‘polinton-like’ viruses into a new family (Phypoliviridae) within a new order Archintovirales; establishment of a new phylum (Commensaviricota) in the kingdom Shotokuvirae; the establishment of a new family called Filamentoviridae with two new genera and three new species; the addition of four new genera in the family Anelloviridae with 70 new species; and the addition of 85 new species in the families Adenoviridae (n=16), Baculoviridae (n=5), Circoviridae (n=5), Parvoviridae (n=55) and Polyomaviridae (n=4). Also, in the family Belpaoviridae, 11 species were renamed to comply with the binomial requirement for species names.

In March 2025, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote, newly proposed taxa were added to those under the mandate of the Plant Viruses Subcommittee. In brief, 1 new order, 3 new families, 6 new genera, 2 new subgenera and 206 new species were created. Some taxa were reorganized. Genus Cytorhabdovirus in the family Rhabdoviridae was abolished and its taxa were redistributed into three new genera Alphacytorhabdovirus, Betacytorhabdovirus and Gammacytorhabdovirus. Genus Waikavirus in the family Secoviridae was reorganized into two subgenera (Actinidivirus and Ritunrivirus). One family and four previously unaffiliated genera were moved to the newly established order Tombendovirales. Twelve species not assigned to a genus were abolished. To comply with the ICTV mandate of a binomial format for virus species, eight species were renamed. Demarcation criteria in the absence of biological information were defined in the genus Ilarvirus (family Bromoviridae). This article presents the updated taxonomy put forth by the Plant Viruses Subcommittee and ratified by the ICTV.

An erratum of this article has been published full details can be found at 10.1099/jgv.0.002144

The Fungal and Protist Viruses Subcommittee (SC) of the International Committee on Taxonomy of Viruses (ICTV) has received a total of eight taxonomic proposals for the 2024 annual cycle. The extent of proposed changes varied, including nomenclatural updates, creation of new taxa and reorganization of established taxa. Following the ICTV procedures, all proposals were reviewed and voted upon by the members of the Executive Committee with ratification in March 2025. As a result, a total of 52 species in the families Botourmiaviridae and Marnaviridae were renamed to comply with the mandated binomial format. A new genus has been added to the dsRNA virus family Amalgaviridae, while two new families, Splipalmiviridae (Wolframvirales) and Mycoalphaviridae (Hepelivirales), were created to classify new groups of positive-sense (+) RNA mycoviruses. The class Arfiviricetes (Cressdnaviricota) was expanded by a new order Lineavirales and a new family Oomyviridae of ssDNA viruses. Additionally, a new class Orpoviricetes was created in the kingdom Orthornavirae to classify a group of bisegmented (+)RNA viruses reported from fungi and oomycetes. Finally, the order Pimascovirales was reorganized to better depict evolutionary relationships of pithoviruses and related viruses with large dsDNA genomes. The summary of updates in the taxonomy of fungal and protist viruses presented here is limited to taxa within the remit of this Subcommittee. For information on taxonomy changes on other fungal viruses closely related to animal and/or plant viruses, please see reports from sister ICTV Subcommittees (i.e. Plant Virus SC and Animal dsRNA and ssRNA(−) Viruses SC).

During the 56th annual meeting of the International Committee on Taxonomy of Viruses (ICTV), held in Bari, Italy, in August 2024, two technical proposals were presented. The first called for amended versions of accepted taxonomic proposals to be named in such a way to ensure that they are readily accessible on the ICTV website (2024.001G). The second proposed a substantial reformatting of the ICTV statutes and codes to produce a more unified text after the numerous changes made to both documents in previous years (2024.002G). Finally, the ICTV Executive Committee (EC) nominated Professor Stuart Siddell as a Life Member of the ICTV for his work over four decades on virus taxonomy, including 16 years as a member of the EC (2024.003G).

An erratum of this article has been published full details can be found at 10.1099/jgv.0.002145

The International Committee on Taxonomy of Viruses (ICTV) holds a ratification vote annually following the review of newly proposed taxa by ICTV Study Groups and members of the virology community. This article reports changes to the taxonomy of viruses infecting archaea that were approved and ratified by the ICTV in March 2025. Six new families of head-tailed viruses expanded the order Caudoviricetes (realm Duplodnaviria); one new family of filamentous viruses was added to the order Ligamenvirales (realm Adnaviria); one new family of viruses with pleomorphic virions was included within a new phylum, new order and new class in the kingdom Trapavirae (realm Monodnaviria); finally, three new families were created for spindle-shaped viruses that remain unassigned to higher level taxa. The 25 new species represent viruses infecting a broad range of archaea, including members of the classes Archaeoglobi, Bathyarchaeia, Methanobacteria, Methanomicrobia, Nitrososphaeria and Poseidoniia. Most of these viruses have been discovered by metagenomics in samples derived from diverse environments, including ambient and extreme marine ecosystems, the gastrointestinal tract of humans and animals, anaerobic digesters and terrestrial hot springs. Following this taxonomic update, archaeal viruses are officially classified into a total of 163 virus species in 94 genera within 62 families.

The haemagglutinin (HA) proteins of contemporary human H3N2 influenza viruses are heavily glycosylated. Glycans influence the protein’s receptor-binding properties and antigenic profile and can be lost when candidate influenza vaccine strains are propagated in embryonated chicken eggs. Glycan changes in egg-derived vaccine strains have been linked to reduced vaccine effectiveness in inactivated influenza vaccines due to changes in antigenicity, but this has not been investigated in live attenuated influenza vaccines (LAIVs). Here, we determined the impact of egg-adaptive glycosylation changes on the antigenicity of two H3N2 LAIV strains which lost an N-linked glycan site due to egg adaptation: A/New Caledonia/71/2014 (LAIV strain for the 2016–18 influenza seasons) and A/Kansas/14/2017 (LAIV strain for the 2019–20 influenza season). Glycosylation of these egg-adapted HA proteins, along with cell-adapted HA proteins from the same strains, was characterized using nano-liquid chromatography-MS, and their antigenic profiles were assessed with microneutralization assays. We found that the absent glycan sites in the egg-adapted strains were present and occupied by a glycan in the respective cell-adapted strains. Despite this, ferret sera raised against the egg-adapted A/New Caledonia/71/2014 strain were still able to effectively neutralize its glycosylated, cell-adapted counterpart and could also neutralize representatives of most circulating clades from 2016 to 2018. Sera raised against egg-adapted A/Kansas/71/2014 showed reduced cross-reactivity to its cell-adapted counterpart, but this effect was primarily driven by a separate egg adaptation, D190N, rather than the glycosylation change. These data show that glycan loss in LAIV HA proteins due to egg adaptation does not necessarily result in antigenic changes relative to cell-derived viruses.

A marked increase in the incidence of mortality amongst wild mammals attributed to infection with highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b viruses was observed in Europe in 2021. Neurological signs and high viral antigen levels in the brain of infected wild mammals indicate that the HPAI H5N1 virus causes severe disease in mammals, but serological analysis suggests that infections may be more widespread, implying that some mammals could experience mild disease. The clinical manifestation and transmissibility of HPAI H5N1 clade 2.3.4.4b viruses amongst mammals represent critical risk factors for potential zoonotic transmission to humans. This study examined the pathogenicity, viral tissue tropism and associated pathology of three HPAI H5N1 viruses in ferrets, which are a model for influenza A infection in humans. Ferrets were experimentally infected with an HPAI H5N1 poultry virus (genotype C) and two HPAI H5N1 viruses (genotype BA) isolated from a red fox, one of which carries the zoonotic PB2-E627K mutation. The red fox isolate, but not the poultry isolate, caused high morbidity, viral shedding and mortality in ferrets. Transmission to co-housed ferrets was investigated in a group setting for the virus carrying the PB2-E627K mutation and caused neurological signs accompanied by prominent viral antigen staining in recipient ferrets compared to directly inoculated ferrets. This study shows that HPAI H5N1 clade 2.3.4.4b viruses can infect mammals with varying pathogenicity and that mammal-to-mammal transmission can occur. This increases the zoonotic potential of the virus and highlights the need for enhanced surveillance in wild mammals for early detection of potential zoonotic threats.

RNA interference is crucial in post-transcriptional gene silencing. Short hairpin RNA (shRNA) is particularly effective because it forms fully complementary matches with target mRNA, leading to its degradation. However, shRNA processing relies on nuclear microprocessors like Drosha, posing a challenge for RNA viral vectors that replicate exclusively in the cytoplasm. Although there have been reports of Drosha translocating to the cytoplasm upon viral infection, many RNA viruses, including Newcastle disease virus (NDV), remain inadequately studied in this context and, in some cases, fail to induce Drosha translocation for shRNA processing. In this study, we developed a novel approach to translocate an shRNA, expressed by NDV as an RNA viral vector, into the nucleus for Drosha processing. As a proof of concept, a recombinant NDV expressing the shRNA (rAF-shmcherry) with an AU-rich region at its 3′ end in the expression cassette was constructed. This shRNA targets a constitutively expressed mCherry gene in a colorectal cancer cell line, SW620-mC. We confirmed the presence of the AU-rich shRNA in the nuclei of the rAF-shmcherry-infected SW620-mC using reverse transcription PCR (RT-PCR). The gene-silencing effect of the shRNA was then evaluated at mRNA and protein levels, showing ~90% downregulation of the mCherry transgene at 24 h post-infection and 70% downregulation of mCherry protein in SW620-mC at 48 h post-infection. This study marks the first exploration of NDV as an shRNA viral vector, presenting a promising approach for shRNA translocation that could be applicable to various RNA viruses.

The genome of human coronavirus 229E (HCoV-229E), a causative agent of human respiratory infections, encodes a unique accessory gene, ORF4. Analysis of laboratory strains and clinical specimens has suggested that HCoV-229E acquires truncating mutations in ORF4 under standard laboratory culture conditions. This study confirmed that HCoV-229E from patients with acute respiratory infections harboured a full-length ORF4 (219 amino acids). In contrast, virus stocks derived from the same patients and passaged in conventional cultured cells [LLC-MK2, human embryonic fibroblast (HEF); HEF, HeLa] exhibited truncated ORF4 of various lengths, such as 168, 143 and 16 amino acids. However, when these virus stocks were propagated in human bronchial/tracheal epithelial cells (HBTECs) cultured at the air–liquid interface (ALI), the full-length ORF4 was selected and stably maintained throughout a prolonged observation period. These findings highlight the importance of ORF4 in patients and under physiologically relevant conditions, and the HBTEC-ALI culture system is valuable for analyzing the native properties of HCoV-229E with an intact full-length ORF4.

A hallmark of the dengue virus (DENV) infection is the manipulation of host cell membranes, lipid trafficking and lipid droplets (LD), all cellular functions that depend on the cytoskeleton and the cytoplasmic streaming system. We previously reported the interaction between the DENV non-structural (NS1) protein and members of the kinesin motor complex in the Aedes albopictus cell line C6/36. In this work, we present evidence indicating that the protein kinesin light chain 1 (KLC1) is indeed a susceptibility factor for the DENV replicative cycle in mosquito cells. The interaction between NS1 and KLC1 was confirmed by proximity ligation and co-immunoprecipitation assays in cells harvested 24 hpi. In addition, transmission immunoelectron microscopy showed KLC1 decorating the surface of vacuoles in association with NS1. Increased levels of KLC1 were observed starting at 6 hpi, suggesting that virus infection stimulates KLC1 synthesis. Silencing KLC1 expression results in a reduction in viral genome synthesis, decreased secretion of NS1 and a reduction of virus progeny by nearly 1 log. In agreement, similar affectations were observed in infected cells transfected with a peptide that competes and interferes with the interaction between KLC1 and its cargo molecules. Of note, both silencing the expression and interfering with the function of KLC1 resulted in a disorganization of LD, which decreased in number and increased in area, in mock or infected cells. These results, taken together, suggest that KLC1 is a host susceptibility factor for DENV in mosquito cells and appears to play an important role in the proper transport and homeostasis of LD required for flavivirus replication. However, modest colocalization was observed between NS1 and LD, and the significance of the KLC1 and NS1 interactions needs to be further investigated.

Recent studies have reported a genotype 4 (G4) reassortant Eurasian avian-like (EA) H1N1 virus in swine, demonstrating a potential pandemic threat in humans. Here, we have compared the tropism, replication competence and pro-inflammatory cytokine and chemokine induction of the two G4 EA H1N1 strains in parallel with 2009 pandemic H1N1 (H1N1/pdm/09) and A/Quail/HK/G1/1997 H9N2 (G1) using ex vivo culture of the human respiratory tract and in vitro culture of human peripheral blood-derived macrophages. Our results showed that G4 strains could replicate in ex vivo cultures of human lung and bronchus with a similar replication competence to H1N1/pdm/09. The cytokine induction levels of G4 were similar to H1N1/pdm/09 in macrophages. Taken together, we could extrapolate that the G4 EA H1N1 swine influenza may pose a notable public health threat towards human and should not underestimate this threat.

Marek’s disease (MD) is a lethal lymphoma of chickens, which is caused by MD virus (MDV), an alphaherpesvirus. MDV infects epithelial cells of the skin appendages, notably feather follicles, replicates in these cells and is shed into the environment exclusively from these tissues. Here, we tested whether chicken skin equivalents (SEs) can be used to model MDV infection. Primary chicken keratinocytes were seeded on a suspension of fibroblasts in collagen and induced to terminally differentiate at the air-liquid interface. A recombinant MDV expressing the Katushka fluorescent protein (MDV-KAT) was introduced into SEs by seeding primary keratinocytes together with MDV-KAT-infected keratinocytes of the K8 cell line. KAT-mediated fluorescence increased during the culture of infected SEs, indicating virus infection and replication, while the expression of keratinocyte differentiation markers was not significantly altered by MDV infection. MDV did not spread to the dermal compartment of SEs but localized to the upper layers of the epidermis. Viral particles were readily observed by electron microscopy in living keratinocytes and for the first time in cornified keratinocytes of the outermost layer of infected SEs, suggesting that viral elements can be released into the environment. Finally, we demonstrated that two fluorescent vaccine strains of MDV, Rispens and herpesvirus of turkey, can infect and replicate in SEs. Taken together, this study establishes chicken SEs as an in vitro model for essential steps of MDV infection.

A corrigendum of this article has been published full details can be found at https://doi.org/10.1099/jgv.0.002162 .

Mpox (formerly known as monkeypox) virus (MPXV) is the zoonotic pathogen of mpox disease in humans. Its increasing emergence outside of its endemic area has heightened the importance of investigating the virus’ prevalence and maintenance in sylvatic reservoirs. The common brown rat (Rattus norvegicus) can inhabit almost anywhere in the UK, posing a threat to zoonotic transmission to humans. Two independent studies were carried out; the first investigated the susceptibility of brown rats to MPXV infection with a clade IIb mpox strain via two challenge routes: intranasal and intradermal. The second study considered the transmission of MPXV between challenged and naïve brown rats. All animals were asymptomatic to mpox disease, although enzyme-linked immunosorbent assay (ELISA) confirmed subclinical infection in challenge groups. In the susceptibility study, reverse transcription PCR (RT-PCR) detected mpox DNA in the lung tissue and throat swabs within the intranasally inoculated group, in addition to viable virus observed from the intranasal throat swabs. In contrast, no virus was detected in either tissues or swabs in the intradermally inoculated group or control group. RT-PCR results from the transmission study detected mpox DNA in tissues and throat swabs taken from challenged animals. Viable virus was observed from tissues and swabs of intranasally challenged animals with infectious titres of ~102–104 TCID50 per millilitre. ELISA assays in the transmission study showed replicable results compared to the first susceptibility study in directly challenged animals alongside evidence of seroconversion in co-housed naïve animals. In conclusion, brown rats are susceptible to MPXV infection, as they have been demonstrated to maintain viable virus in the absence of clinical signs. Viral transmission of MPXV from infected rats to naïve rats was not observed by RT-PCR, although naïve rats did show antibody responses when exposed to infected rats indicating exposure to virus.