Mammalian Adaptation Research Articles

Savanna ecosystems and mammalian adaptations in Mid-Miocene Northern China

Savanna ecosystems and mammalian adaptations in Mid-Miocene Northern China

Molecular evolution of TRPC4 regulatory sequences supports a role in mammalian thermoregulatory adaptation

Background Proteins encoded by the canonical transient receptor potential (Trpc) gene family form transmembrane channels involved in diverse signal-transduction pathways. Trpc4 has been shown necessary for the induction of nonshivering thermogenesis (NST) in mice, a key component of which is thermogenic brown adipose tissue (BAT). In bats, Trpc4 exhibited diversifying selection within exons encoding regulatory binding sites of TRPC4. Methods To assess whether diversification of these regulatory sequences mirrors the diversification of mammalian thermoregulatory strategies, the ratio of nonsynonymous to synonymous substitutions (ω) was estimated for multiple tetrapod outgroups and eutherian orders. Four questions were addressed: (1) Did the ancestral eutherian Trpc4 diverge under positive selection from nonplacental mammals that lack BAT? (2) Did Trpc4 subsequently become more constrained in descendant eutherian clades? (3) In eutherian clades that subsequently lost BAT by inactivation of the thermogenin gene Ucp1, did Trpc4 become less constrained? (4) Does the evolutionary rate of Trpc4 differ between quantitatively more heterothermic mammal orders (bats and rodents) relative to quantitatively less heterothermic outgroups (carnivores, artiodactylids, and primates)? Results Coincident with the advent of BAT, Trpc4 evolutionary rate increased significantly in ancestral eutheria after their divergence from nonplacental mammals but a branch-site model did not support a rate class ω > 1 along that branch. In descendant eutherian mammals, Trpc4 became far more constrained, with an evolutionary rate less than half that of tetrapod clades lacking NST, a pattern was not seen in other Trp channel genes. Intensifying selection in descendent eutherian mammals was further supported with the RELAX program, which also indicated reduced constraint on Trpc4 in clades that have secondarily lost BAT. However, no consistent pattern was identified within mammalian orders with strong variation in heterothermy: evidence of increased evolutionary rate was again found in bats for Trpc4 as well as homologs it directly binds in heteromeric membrane channels (Trpc5 and Trpc1), yet all rodent Trpc genes had low evolutionary rates. Evolutionary rates of Trpc4 and Trpc1 in bats were consistent with relaxed constraint whereas bat Trpc5 experienced diversifying selection. Most variation among tetrapod TRPC4 sequences lies within an 85 amino-acid window that is functionally uncharacterized. Sequence alignments demonstrated that the TRPC4 β isoform, which lacks a portion of the C-terminal regulatory region, originated in basal eutherians but appears to be lost in many tip lineages. Collectively, the data indicate that the C-terminal region of TRPC4 has responded to selection on NST thermoregulation during the diversification of eutherian mammals. The drivers of increased diversification of Trpc4 and interacting genes in bats remain to be determined.

Progressive Adaptation of Subtype H6N1 Avian Influenza Virus in Taiwan Enhances Mammalian Infectivity, Pathogenicity, and Transmissibility.

The interspecies transmission of avian influenza viruses remains a significant public health concern. H6 viruses have gained attention following the first human infection by a chicken-origin H6N1 virus (A/Taiwan/02/2013, Hu/13), highlighting their zoonotic potential. To understand the evolutionary trajectory and mammalian adaptation of this Taiwan lineage, we compared two avian isolates (A/Chicken/Taiwan/CF19/2009, Ck/09; A/Chicken/Taiwan/2267/2012, Ck/12) and Hu/13 in vitro and in vivo. Hu/13 exhibited enhanced replication in MDCK cells, producing larger plaques and higher viral titers than Ck/09 and Ck/12. In BALB/c mice, Hu/13 demonstrated the highest pathogenicity and mortality, followed by Ck/12, while Ck/09 induced minimal morbidity. Hu/13 and Ck/12 replicated efficiently in respiratory tissues, eliciting robust cytokine responses and severe pulmonary lesions. In ferrets, Hu/13 showed relatively efficient transmission, infecting all direct physical-contact and two out of three airborne-contact ferrets, whereas Ck/09 failed to transmit. Histopathology confirmed escalating lung pathology from Ck/09 to Ck/12 and Hu/13. Whole-genome sequencing identified adaptive mutations in Hu/13 during ferret replication, though no canonical mammalian-adaptive changes (e.g., PB2-E627K or HA-Q226L) were detected. These findings demonstrate progressive mammalian adaptation, replication efficiency, and transmissibility within the Taiwan H6N1 lineage. Enhanced surveillance is crucial to monitor mammalian-adaptive mutations, informing pandemic preparedness and public health strategies.

Genomic changes of Lassa virus associated with mammalian host adaptation

BackgroundLassa virus (LASV) causes a severe haemorrhagic fever in humans, with estimates of 100,000 to 300,000 infections annually in endemic regions and accounting for around 5000 deaths. The natural reservoir is the Mastomys rat, but through zoonotic transmissions humans are accidental hosts. Regular outbreaks continue to exert pressures on public health systems, with its ability to cause nosocomial infections posing risks to healthcare workers. It is a concern that larger outbreaks and introduction of LASV to new territories will intensify, including risk of adaptation to new mammalian host reservoirs.ResultsTo evaluate genetic changes in LASV during adaptation to a new host, a guinea pig model of infection was utilised. Initial infection with LASV stocks cultured from cell culture resulted in only mild or subclinical disease. To study the susceptibility in naïve animals, the virus was serially passaged which increased clinical signs during disease progression ultimately resulting in severe disease. An RNAseq and consensus mapping approach was undertaken to evaluate nucleotide changes in LASV genome from each animal at each passage.ConclusionsDuring adaptation to guinea pigs, no significant new mutations occurred. Instead, a selection pressure on two genes of the L segment was observed resulting in their increased frequency in the genome population during passaging.

Genetic diversity of A(H5N1) avian influenza viruses isolated from birds and seals in Russia in 2023

Thousands of outbreaks of the highly pathogenic avian influenza A(H5N1) virus in birds and an increasing number of mammal infections are registered annually. In 2023, multiple avian influenza outbreaks were registered among wild birds, poultry and seals in Russia. The genetic characterization of seventy-seven avian viruses and three viruses from seals showed that they belonged to the 2.3.4.4b clade and represented four distinct reassortant genotypes. The majority of viruses represented genotype BB, which was widespread in Europe in 2023. Viruses from seals and four viruses from birds, isolated from outbreaks in the Far East region, belonged to the G1 (A3) genotype and had the amino acid substitution N319K in the NP protein, previously associated with an increased virulence for mammals. In addition, one virus of the G10 genotype and two viruses, representing a previously undescribed genotype (designated as Ru-23-G4) were identified. The viruses analyzed showed normal inhibition by neuraminidase inhibitors. Seven viruses had genetic markers of amantadine resistance. All the influenza A(H5N1) viruses studied showed a binding preference for α2-3-linked sialic acids, suggesting a low risk of transmission among humans. Nevertheless, monitoring of reassortment and mammalian adaptation mutations is essential for the timely identification of viruses with increased pandemic potential.

Evidence of novel reassortment in clade 2.3.4.4b avian influenza H5N1 viruses, India, 2024.

Evidence of novel reassortment in clade 2.3.4.4b avian influenza H5N1 viruses, India, 2024.

Muscle Adaptations to Hyperglycemia Enable Nectar Bats to Thrive on a Sugar-Rich Diet

Nectar-feeding bats, often referred to as "hummingbirds of the night," thrive on sugar-rich diets that induce extreme postprandial hyperglycemia exceeding 750 mg/dL, levels intolerable for most mammals. To investigate the metabolic adaptations underlying this resilience, we compared closely related bat species with divergent diets using RNA sequencing of muscle tissue, proteomic analyses from serum samples, and physiological studies focusing on glucose and insulin dynamics. Functional ex vivo muscle experiments reveal insulin resistance in nectar bats, with diminished pAKT activation despite high circulating glucose levels. However, these bats exhibit insulin-independent glucose uptake, facilitated by muscle contractions and alternative glucose transporters, alongside muscle-specific expression of gck (glucokinase), which supports rapid glucose metabolism. Muscle tissue in nectar bats also shows increased triglyceride storage, indicating that excess glucose is directed toward fat production rather than glycogen storage. Additional adaptations include differential mTOR expression, contributing to metabolic flexibility and energy utilization for flight. Unlike other mammals with insulin resistance, nectar bats lack substantial adipose tissue, underscoring the central role of muscle in postprandial glucose regulation. These findings provide a comprehensive view of how nectar bats achieve metabolic resilience, offering novel insights into mammalian adaptations to extreme dietary pressures. Supported by NSF Postdoctoral Fellowship #2109717, BWF Diversity Enrichment Program #G-1022339, and HHMI Hanna H. Gray Fellowship #GT-15991 to J.C. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Synergistic effects of PA (S184N) and PB2 (E627K) mutations on the increased pathogenicity of H3N2 canine influenza virus infections in mice and dogs.

As companion animals, dogs are susceptible to various subtypes of influenza A virus (IAV), with the H3N2 and H3N8 subtypes of canine influenza virus (CIV) stably circulating among canines. Compared to the H3N8 CIV, the H3N2 CIV is more widely prevalent in canine populations and demonstrates increased adaptability to mammals, potentially facilitating cross-species transmission. Therefore, a comprehensive elucidation of the mechanisms underlying H3N2 CIV adaptation to mammals is imperative. In this study, we serially passaged the GD14-WT strain in murine lungs, successfully establishing a lethal H3N2 CIV infection model. From this model, we isolated the lethal strain GD14-MA and identified the key lethal mutations PA(S184N) and PB2(E627K). Moreover, the GD14-ma[PA(S184N)+PB2(E627K)] strain exhibited markedly enhanced pathogenicity in dogs. Viral titers in lung tissues from infected dogs and mice showed that GD14-ma[PA(S184N)+PB2(E627K)] does not increase its pathogenicity to mice and dogs by upregulating viral titers compared to the GD14-WT strain. Notably, sequence alignments across all H3N2 IAVs showed an increasing prevalence of the PA (S184N) and PB2 (E627K) mutations from avian to human hosts. Finally, single-cell RNA sequencing of infected mouse lung tissues showed that GD14-ma[PA(S184N)+PB2(E627K)] effectively evaded host antiviral responses, inducing a robust inflammatory reaction. Considering the recognized role of the PB2 (E627K) mutation in the mammalian adaptation of IAVs, our findings underscore the importance of ongoing surveillance for the PA (S184N) mutation in H3N2 IAVs.IMPORTANCESince the 21st century, zoonotic viruses have frequently crossed species barriers, posing significant global public health challenges. Dogs are susceptible to various influenza A viruses (IAVs), particularly the H3N2 canine influenza virus (CIV), which has stably circulated and evolved to enhance its adaptability to mammals, including an increased affinity for the human-like SAα2,6-Gal receptor, posing a potential public health threat. Here, we simulated H3N2 CIV adaptation in mice, revealed that the synergistic PA(S184N) and PB2(E627K) mutations augment H3N2 CIV pathogenicity in dogs and mice, and elucidated the underlying mechanisms at the single-cell level. Our study provides molecular evidence for adapting the H3N2 CIV to mammals and underscores the importance of vigilant monitoring of genetic variations in H3N2 CIV.

Epizootiological and Epidemiological Situation on Highly Pathogenic Avian Influenza Globally and in the Russian Federation in 2024

The aim of the work was to analyze the circulation of the most epidemiologically significant variants of the avian influenza virus in the world and across Russia in 2024. The global situation on highly pathogenic avian influenza remained tense in 2024. The disease affected 68 countries, resulting in the death or culling of about 19 million poultry. In addition, there was a large number of influenza A(H5N1) virus detections in wild and domestic mammals, predominantly in the United States. Those included outbreaks on dairy farms that affected herds throughout the year, encompassing more than 900 dairy farms in 16 states by the year’s end and causing infection of 40 farm workers in four states. The A(H5N1) viruses detected in farm workers contained mammalian adaptation mutations. In total, more than 100 human infections with zoonotic variants of influenza virus were reported in 2024, with influenza A(H5N1) virus detected in 81 cases. Apart from outbreaks of A(H5N1), other influenza virus variants, such as A(H5N6), A(H5N8), A(H5N5), A(H5N2), were circulating worldwide. Outbreaks among poultry caused by different subtypes of influenza A(H7) virus were also reported in a number of countries. In Russia, the situation on highly pathogenic influenza virus in 2024 was less tense. All detected influenza A(H5N1) viruses belonged to clade 2.3.4.4b and were genetically similar to the vaccine strains recommended by WHO. Isolated strains were antigenically similar to a reference strain A/goose/Tyumen/359- 13/2021(H5N1), which had HA1 sequence identical to the vaccine strain A/Astrakhan/3212/2020(H5N8). In addition, an influenza A(H9N2) virus was isolated in 2024. The study of this strain showed that it belongs to the clade Y439 and does not contain mutations associated with increased pathogenicity and drug resistance.

Highly Pathogenic Avian Influenza Virus in Mammals: Lack of Detection in Cattle With Respiratory Tract Infections and Genetic Analysis of Sporadic Spillover Infections in Wild Mammals in Bavaria, Southern Germany, 2022-2023.

In 2021, the H5N1 clade 2.3.4.4b Avian Influenza Viruses (AIVs) emerged on the American continent. At the same time, a further global spread took place. Infections have been reported in avian species as well as in over 50 mammalian species in 26 countries, and often result in severe disease with notable neurological pathology. Outbreaks in dairy cattle in the United States in 2024 illustrate viral transmission at a non-traditional interface and cross-species transmission. This development raises significant global concern regarding the virus's potential for wider spread. Given that H5N1 infections in birds reached record-high levels in Germany by late 2022, it is important to investigate whether Influenza A Virus (IAV) infections were also occurring in mammals sharing habitats with wild birds. Selected wild and domestic mammal populations were monitored over a two-year period (from January 2022 to December 2023), which coincided with a major infection period in wild birds in Bavaria. Genomes of Highly Pathogenic Avian IAV H5N1 (clade 2.3.4.4b) were detected in red foxes but not in samples from ruminants such as red deer or domestic cattle. Analyses of viral whole genome sequences revealed several mutations associated with mammalian adaptation. Our results indicate a high frequency of spillover events to red foxes at a time when there was a peak of H5N1 infections in wild birds in Bavaria. Phylogenetic analyses show no specifically close genetic relationship between viruses detected in mammalian predators within a geographic area. While direct fox-to-fox transmission has not yet been reported, the H5N1 clade 2.3.4.4b AIVs' ability to spread through non-traditional interfaces and to cross species barriers underlines the importance of continuous IAV surveillance in mammals and possibly including previously unknown host species.

Cross-species and mammal-to-mammal transmission of clade 2.3.4.4b highly pathogenic avian influenza A/H5N1 with PB2 adaptations

Highly pathogenic H5N1 avian influenza viruses (HPAIV) belonging to lineage 2.3.4.4b emerged in Chile in December 2022, leading to mass mortality events in wild birds, poultry, and marine mammals and one human case. We detected HPAIV in 7,33% (714/9745) of cases between December 2022–April 2023 and sequenced 177 H5N1 virus genomes from poultry, marine mammals, a human, and wild birds spanning >3800 km of Chilean coastline. Chilean viruses were closely related to Peru’s H5N1 outbreak, consistent with north-to-south spread down the Pacific coastline. One human virus and nine marine mammal viruses in Chile had the rare PB2 D701N mammalian-adaptation mutation and clustered phylogenetically despite being sampled 5 weeks and hundreds of kilometers apart. These viruses shared additional genetic signatures, including another mammalian PB2 adaptation (Q591K, n = 6), synonymous mutations, and minor variants. Several mutations were detected months later in sealions in the Atlantic coast, indicating that the pinniped outbreaks on the west and east coasts of South America are genetically linked. These data support sustained mammal-to-mammal transmission of HPAIV in marine mammals over thousands of kilometers of Chile’s Pacific coastline, which subsequently continued through the Atlantic coastline.

Dynamics of a Panzootic: Genomic Insights, Host Range, and Epidemiology of the Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b in the United States.

In late 2021, Eurasian-lineage highly pathogenic avian influenza (HPAI) A(H5N1) viruses from HA clade 2.3.4.4b were first detected in the United States. These viruses have caused severe morbidity and mortality in poultry and have been detected in numerous wild and domestic animals, including cows and humans. Notably, infected cows transmitted the virus to cats, causing extreme pathogenicity and death. While human-to-human spread of the virus has not been recorded, efficient transmission of the bovine-origin virus has also led to extreme pathogenicity and death in ferret models. Recently, markers in PB2 (E627K) and HA (E186D, Q222H), indicating mammalian adaptation mutations, were detected in an H5N1-infected patient manifesting critical illness in Canada. These, combined with instances of interspecies spread of the virus, have raised global public health concerns. This could highlight the potential for the virus to successfully adapt to mammals, posing a serious risk of a global outbreak. A One Health approach is, thereby, necessary to monitor and control the outbreak. This review aims to analyze the epidemiology, transmission, and ecological impacts of HPAI A(H5N1) clade 2.3.4.4b in the U.S., identify knowledge gaps, and inform strategies for effective outbreak management and mitigation.

Steppe development and mammalian adaptation in the middle Miocene, North Junggar Basin, Central Asia

Steppe development and mammalian adaptation in the middle Miocene, North Junggar Basin, Central Asia

Chicken ANP32A-independent replication of highly pathogenic avian influenza viruses potentially leads to mammalian adaptation-related amino acid substitutions in viral PB2 and PA proteins.

Acidic nuclear phosphoprotein 32 family member A (ANP32A) is an important host factor that supports the efficient replication of avian influenza viruses (AIVs). To develop an antiviral strategy against Gs/Gd-lineage H5 highly pathogenic avian influenza (HPAI) viruses in chickens, we established chicken ANP32-knockout (chANP32A-KO) DF-1 cells and evaluated their antiviral efficacy through in vitro validation. The replication of all HPAI viruses tested in chANP32A-KO cells was significantly lower compared to that of wild-type DF-1 cells. However, when HPAI strains A/mountain hawk-eagle/Kumamoto/1/2007 (H5N1; MHE) and A/chicken/Aichi/2/2011 (H5N1; H5Aichi) were passed in chANP32A-KO cells, mutant viruses were generated, which exhibited comparable replication levels in both chANP32A-KO and wild-type DF-1 cells. Sequence analysis revealed that mammalian-adaptive amino acid mutations PB2_D256G and PA_T97I were present in the MHE mutant virus, and the PB2_E627K mutation was identified in the H5Aichi mutant virus. These mutations have also been reported to enhance the polymerase activity of AIVs in mammalian cells; however, the minigenome assay in the present study showed that the polymerase activity of mutant viruses in chANP32A-KO cells was not restored to levels comparable to those in wild-type DF-1 cells. These findings suggest that ANP32A-independent viral replication may induce amino acid substitutions associated with mammalian adaptation in AIVs. They also imply that the high efficiency of viral replication mediated by these amino acid mutations may not result from enhanced polymerase activity but rather involve other undefined mechanisms.IMPORTANCEDuring the host-switching of avian influenza viruses (AIVs) to mammalian hosts, introducing adaptive mutations into viral proteins is essential to ensure optimal functionality through virus-host protein interactions in mammalian cells. However, the mechanisms leading to adaptive mutations in viral proteins remain unclear. Among several host proteins that promote viral growth, acidic nuclear phosphoprotein 32 family member A (ANP32A) is known to be an important factor for efficient viral replication. Here, we generated mutant highly pathogenic avian influenza viruses capable of ANP32A-independent replication in a chicken-derived cell line. We demonstrated that several amino acid mutations found in the mutant viruses correspond to those associated with the mammalian adaptation of AIVs. These results suggest that ANP32A-independent viral replication is one of the mechanisms for introducing amino acid mutations that are reportedly involved in the mammalian adaptation of AIVs.

Isoleucine at position 137 of haemagglutinin acts as a mammalian adaptation marker of H9N2 avian influenza virus

ABSTRACT The H9N2 subtype of avian influenza virus (AIV) is widely distributed among poultry and wild birds and is also a threat to humans. During AIV active surveillance in Liaoning province from 2015 to 2016, we identified 10 H9N2 strains exhibiting different lethality to chick embryos. Two representative strains, A/chicken/China/LN07/2016 (CKLN/07) and A/chicken/China/LN17/2016 (CKLN/17), with similar genomic background but different chick embryo lethality, were chosen to evaluate the molecular basis for this difference. A series of reassortants between CKLN/07 and CKLN/17 were generated and their chick embryo lethality was assessed. We found that the isoleucine (I) residue at position 137 (H3 numbering) in the haemagglutinin (HA) was responsible for the chick embryo lethality of the H9N2 virus. Further studies revealed that the threonine (T) to I mutation at HA position 137 enhanced viral replication in vitro and in vivo. Moreover, the HA-T137I substitution in H9N2 avian influenza virus increased the guinea pig transmission efficiency. We also found that the HA-T137I substitution was critical for α2,6-linked sialic acid binding preference and HA activation and stability of H9N2 virus. Our findings demonstrated that HA-137I is a key molecular marker for mammalian adaptation of H9N2 AIV.

Preparedness, prevention and control related to zoonotic avian influenza.

A risk assessment framework was developed to evaluate the zoonotic potential of avian influenza (AI), focusing on virus mutations linked to phenotypic traits related to mammalian adaptation identified in the literature. Virus sequences were screened for the presence of these mutations and their geographical, temporal and subtype-specific trends. Spillover events to mammals (including humans) and human seroprevalence studies were also reviewed. Thirty-four mutations associated with five phenotypic traits (increased receptor specificity, haemagglutinin stability, neuraminidase specificity, enhanced polymerase activity and evasion of innate immunity) were shortlisted. AI viruses (AIVs) carrying multiple adaptive mutations and traits belonged to both low and highly pathogenic subtypes, mainly to A(H9N2), A(H7N9), A(H5N6) and A(H3N8), were sporadic and primarily detected in Asia. In the EU/EEA, H5Nx viruses of clade 2.3.4.4b, which have increased opportunities for evolution due to widespread circulation in birds and occasional cases/outbreaks in mammals, have acquired the highest number of zoonotic traits. Adaptive traits, such as enhanced polymerase activity and immune evasion, were frequently acquired, while receptor-specific mutations remained rare. Globally, human cases remain rare, with the majority overall due to A(H5N1), A(H5N6), A(H7N9) and A(H9N2) that are among the subtypes that tend to have a higher number of adaptive traits. The main drivers of mammalian adaptation include virus and host characteristics, and external factors increasing AIV exposure of mammals and humans to wild and domestic birds (e.g. human activities and ecological factors). Comprehensive surveillance of AIVs targeting adaptive mutations with whole genome sequencing in animals and humans is essential for early detection of zoonotic AIVs and efficient implementation of control measures. All preparedness, preventive and control measures must be implemented under a One Health framework and tailored to the setting and the epidemiological situation; in particular, enhanced monitoring, biosecurity, genomic surveillance and global collaboration are critical for mitigating the zoonotic risks of AIV.

E627V mutation in PB2 protein promotes the mammalian adaptation of novel H10N3 avian influenza virus

Since 2021, the novel H10N3 has caused four cases of human infection in China, the most recent of which occurred in December 2024, posing a potential threat to public health. Our previous studies indicated that several avian H10N3 strains are highly pathogenic in mice and can be transmitted between mammals via respiratory droplets without prior adaptation. By analyzing the genome sequence, we found that these H10N3 viruses carry the PB2-E627V mutation, which is becoming increasingly common in several subtypes of avian influenza viruses (AIV); however, its mechanism in mammalian adaptation remains unclear. Using a reverse genetics system, we investigated the role of PB2-E627V in the adaptation of H10N3 to mammals and poultry. Our findings demonstrate that the PB2-E627V mutation is critical for the high pathogenicity of novel H10N3 in mice and its ability to be transmitted through the air among mammals. Additionally, we found that the role of PB2-627 V in promoting AIV adaptation to mammals is comparable to that of PB2-627 K. More importantly, PB2-627 V appears to be equally suited to long-term persistence in poultry. Therefore, using PB2-627 V as a novel molecular marker to assess the epidemic potential of AIV is of great significance for preventing possible influenza pandemics in the future.

Probing the functional constraints of influenza A virus NEP by deep mutational scanning.

The influenza A virus nuclear export protein (NEP) is a multifunctional protein that is essential for the viral life cycle and has very high sequence conservation. However, since the open reading frame of NEP largely overlaps with that of another influenza viral protein, non-structural protein 1, it is difficult to infer the functional constraints of NEP based on sequence conservation analysis. In addition, the N-terminal of NEP is structurally disordered, which further complicates the understanding of its function. Here, we systematically measure the replication fitness effects of >1,800 mutations of NEP. Our results show that the N-terminal domain has high mutational tolerance. Additional experiments show that N-terminal domain mutations affect viral transcription and replication dynamics, host cellular responses, and mammalian adaptation of avian influenza virus. Overall, our study not only advances the functional understanding of NEP but also provides insights into its evolutionary constraints.

A low pathogenic avian influenza A/Mallard/South Korea/KNU2019-34/2019 (H1N1) virus has the potential to increase the mammalian pathogenicity

Influenza, a highly contagious respiratory infectious disease caused by an influenza virus, is a threat to public health worldwide. Avian influenza viruses (AIVs) have the potential to cause the next pandemic by crossing the species barrier through mutation of viral genome. Here, we investigated the pathogenicity of AIVs obtained from South Korea and Mongolia during 2018–2019 by measuring viral titers in the lungs and extrapulmonary organs of mouse models. In addition, we assessed the pathogenicity of AIVs in ferret models. Moreover, we compared the ability of viruses to replicate in mammalian cells, as well as the receptor-binding preferences of AIV isolates. Genetic analyses were finally performed to identify the genetic relationships and amino acid substitutions between viral proteins during mammalian adaptation. Of the 24 AIV isolates tested, A/Mallard/South Korea/KNU2019-34/2019 (KNU19-34; H1N1) caused severe bodyweight loss and high mortality in mice. The virus replicated in the lungs, kidneys, and heart. Importantly, KNU19-34-infected ferrets showed high viral loads in both nasal washes and lungs. KNU19-34 replicated rapidly in A549 and bound preferentially to human like α2,6-linked sialic acids rather than to avian-like α2,3-linked sialic acids, similar to the pandemic A/California/04/2009 (H1N1) strain. Gene segments of KNU19-34 were distributed in Egypt and Asia lineages from 2015 to 2018, and the virus had several amino acid substitutions compared to H1N1 AIV isolates that were non-pathogenic in mice. Collectively, the data suggest that KNU19-34 has zoonotic potential and the possibility of new mutations responsible for mammalian adaptation.

First record of White-Collared Peccary (Dicotyles Tajacu) with Piebaldism across its entire distribution

Coloration is crucial for mammalian adaptation, influencing predator defense and social behavior. In recent decades, chromatic anomalies have been documented in Neotropical mammals, including albinism, leucism, and piebaldism, affecting several species. Piebaldism is a rare autosomal disorder characterized by asymmetric depigmented patches on the body. This study presents the first record of piebaldism in the collared peccary (Dicotyles tajacu Linnaeus, 1758) throughout its distribution. The record was obtained using camera traps at the Estação Ecológica (ESEC) da Terra do Meio in 2023. Observations showed that the affected peccary coexisted normally with other peccaries and engaged in typical feeding and social behaviors, suggesting that piebaldism does not affect individual social interactions. This finding is consistent with the literature indicating that chemical signals are more important than visual signals in Tayassuidae. This finding highlights the need to understand the frequency and distribution of chromatic anomalies to assess their implications for conservation plans over time.