Henipaviruses (HNV), Hendra (HeV) and Nipah (NiV) virus, cause severe pulmonary and neurologic disease in humans and other mammals. Bats in the genus Pteropus naturally host HeV and NiV, but their feasibility in experimental studies is limited due to their large size, low fertility rate, and unavailability outside of their native range. Understanding bat-henipavirus interactions that regulate shedding and replication could improve mitigation of spillover events and illuminate the factors that differentiate severe and controlled HNV infection. Here, we assessed the suitability of the Jamaican fruit bat (JFB) (Artibeus jamaicensis) to model HNV infection in vitro and in vivo. JFB primary kidney cells were permissive to HNVs, and HeV and NiV antagonized the induction of the innate antiviral response. JFBs were inoculated via the intranasal and oral routes (IN/PO) with HeV or NiV or intravenously (IV) with HeV and monitored for 7 days. Following IN/PO exposure, infection was quenched rapidly and limited HeV RNA was detected in oral swabs and tissues while NiV RNA was found in only one oral swab. HeV IV inoculation resulted in robust, disseminated infection and viral RNA was detected in oral, rectal, and environmental swabs. Overall, these results support that JFBs are susceptible to both viruses, but replication is quenched rapidly in vivo following IN/PO exposure. Future studies will optimize the in vivo model to leverage the JFB to further our understanding of bat-henipavirus interactions.

The ongoing outbreak of highly pathogenic avian influenza virus (HPAIV) subtype H5N1 in the U.S. poses a significant public health threat. To date, 70 human cases have been confirmed in the United States, including two severe cases and one fatality. While suitable animal models are crucial for predicting the potential pandemic risk of newly emerging pathogens in humans, studies investigating contemporary HPAIV H5N1 transmission dynamics remain limited. Here, we investigate the pathogenicity and transmission efficiency of recent clade 2.3.4.4b H5N1 viruses isolated from a bovine, mountain lion, and a human case using Syrian hamsters. Intranasal inoculation results in productive virus replication in the respiratory tract and shedding for all three isolates. Transmission studies demonstrate limited efficiency via direct contact and airborne routes for all isolates. Although overall transmission is inefficient, the human H5N1 isolate demonstrates relatively greater contact transmissibility than the bovine and mountain lion isolates. Taken together, our findings demonstrate that the Syrian hamster model complements existing animal models for influenza A virus research and expands the resources available for investigating the pathogenicity, transmissibility, and efficacy of countermeasures against HPAIV H5N1.

Replication of influenza A virus in human nasal epithelium affects transmissibility and disease. We compared virus replication and immune responses in human nasal epithelium infected with seasonal and highly pathogenic avian influenza A(H5N1) viruses. Contemporary H5N1 viruses replicated better than the historical isolate; however, interferon response to B3.13 genotype viruses was dampened.

Diseases caused by henipaviruses, exemplified by Hendra virus and Nipah virus, pose a serious risk to public health because of their epidemic potential and high case-fatality rates and the paucity of medical countermeasures to mitigate them. In December 2024, a group of 150 scientists from 16 countries convened in Geelong, Victoria, Australia, to mark the 30th anniversary of the discovery of Hendra virus. The Hendra@30 conference built upon its predecessor conference held in 2019 in Singapore, Nipah@20, by expanding its program across broader disciplines and integrating sessions on human sociology and disease ecology into the main scientific discussions. We describe key highlights from Hendra@30 and reflect on 4 key elements that have advanced henipavirus research and medical countermeasures research and development. We propose that integrating bat ecology into henipavirus research blueprints will enable development of ecologic countermeasures that prevent spillover and will complement existing preparedness and response efforts with evidence-based prevention strategies.

Since early 2022, highly pathogenic avian influenza (HPAI) H5N1 virus infections have been reported in wild aquatic birds and poultry throughout the USA with spillover into several mammalian species1-6. In March 2024, HPAIV H5N1 clade 2.3.4.4b was first detected in dairy cows in Texas, USA, and continues to circulate on dairy farms in many states7,8. Milk production and quality are diminished in infected dairy cows, with high virus titres in milk raising concerns of exposure to mammals including humans through consumption9-12. Here we investigated routes of infection with bovine HPAIV H5N1 clade 2.3.4.4b in cynomolgus macaques, a surrogate model for human infection13. We show that intranasal or intratracheal inoculation of macaques could cause systemic infection resulting in mild and severe respiratory disease, respectively. By contrast, infection by the orogastric route resulted in limited infection and seroconversion of macaques that remained subclinical.

The highly pathogenic avian influenza (HPAI) A(H5N1) clade 2.3.4.4b viruses, responsible for the current outbreak in dairy cows in the United States, pose a significant animal and public health threat. In this study, we compare disease progression and pathology of three recent clade 2.3.4.4b isolates derived from a cow, a mountain lion, and a mink to a human HPAI A(H5N1) isolate from Vietnam in mice. Inoculating C57BL/6J and BALB/c mice with all four HPAI A(H5N1) isolates results in comparable levels of virus replication in the lung inducing significant local pro-inflammatory cytokine responses and severe respiratory disease. Infecting C57BL/6J mice with the bovine isolate yields high viral titers in the brain, a significant pro-inflammatory cytokine response and neurologic disease. Our findings suggest the recent bovine isolate possesses enhanced neuroinvasive/neurovirulent disease causing fatal respiratory and neurologic disease in C57BL/6J mice.

The emergence of the Omicron lineage represented a major genetic drift in SARS-CoV-2 evolution. This was associated with phenotypic changes including evasion of pre-existing immunity and decreased disease severity. Continuous evolution within the Omicron lineage raised concerns of potential increased transmissibility and/or disease severity. To address this, we evaluate the fitness and pathogenesis of contemporary Omicron variants XBB.1.5, XBB.1.16, EG.5.1, and JN.1 in the upper (URT) and lower respiratory tract (LRT). We compare in vivo infection in Syrian hamsters with infection in primary human nasal and lung epithelium cells and assess differences in transmissibility, antigenicity, and innate immune activation. Omicron variants replicate efficiently in the URT but display limited pathology in the lungs compared to previous variants and fail to replicate in human lung organoids. JN.1 is attenuated in both URT and LRT compared to other Omicron variants and fails to transmit in the male hamster model. Our data demonstrate that Omicron lineage evolution has favored increased fitness in the URT.

Nipah virus (NiV) is an emerging zoonotic pathogen that causes severe respiratory and neurologic disease, and there are currently no licensed vaccines or approved treatments. The acute respiratory disease caused by NiV is associated with severe inflammation, similar to severe COVID-19. Dexamethasone is an affordable and widely available synthetic glucocorticoid, that improved outcomes when administered to patients with severe COVID-19. To determine whether a similar beneficial effect could be achieved during NiV infection, we tested the effect of an anti-inflammatory or immunosuppressive dose of dexamethasone on NiV in the Syrian hamster model. We found that dexamethasone treatment produced the expected hematologic changes in uninfected animals in a dose-dependent manner. In NiV-infected animals, the anti-inflammatory dose of dexamethasone reduced pulmonary pathology, while the immunosuppressive dose had no effect. The anti-inflammatory dose did not increase virus replication in tissues or virus shedding from the respiratory tract, indicating the anti-inflammatory dose of dexamethasone does not result in increased virus replication. Despite reduced lung pathology, dexamethasone treatment did not increase survival after NiV challenge. When dexamethasone treatment was combined with the antiviral remdesivir, dexamethasone negated the increased survival observed in hamsters treated with remdesivir alone. Our study provides critical information on the effect of dexamethasone administration on the outcome of NiV infection and cautions against the use of dexamethasone in combination with other antivirals like remdesivir without preclinical validation.

In this study, we investigated differences in tissue tropism of two HPAI H5N1 strains, the isolate A/Vietnam/1203/2004 (VN1203) isolated from a fatal human case in 2004 and the bovine isolate A/Bovine/Ohio/B24osu-342/2024 (Bov342) isolated in 2024, in C57BL/6J mice. Infection via aerosols was uniformly lethal in mice. However, tissue tropism differed significantly: while VN1203 replication was largely restricted to the respiratory tract, Bov342 successfully replicated in the respiratory tract as well as various regions of the brain. Correspondingly, cytokine profiles in the brain differed significantly between the isolates. Notably, in addition to abundant evidence of CNS infection in Bov342-challenged mice via immunohistochemistry, sporadic intranuclear and intracytoplasmic immunoreactivity was observed in other tissues in the head, including the choroid plexus, retina, and inner ear. This study demonstrates that while both HPAI H5N1 isolates are uniformly lethal in C57BL/6J mice upon aerosol exposure, significant differences exist in tissue tropism.

Background:Clade 2.3.4.4b highly pathogenic avian influenza (HPAI) H5N1 viruses are widely circulating in North America with unprecedented transmission into novel host species. A high incidence of neurologic disease is observed in carnivores infected with clade 2.3.4.4b HPAI H5N1 viruses, and historical outbreaks of HPAI H5N1 in humans are also associated with neurologic complications, raising concerns about neurotropism and neurovirulence of clade 2.3.4.4b HPAI H5N1 viruses. Methods:We analyzed virus replication kinetics, cellular tropism, and host responses to infection in human cerebral organoids (hCOs) inoculated with clade 2.3.4.4b HPAI H5N1 viruses compared to a historical clade 1 HPAI H5N1 virus and a 2007 seasonal influenza A virus. Results:HPAI H5N1 viruses replicated to high titers in hCOs, but replication of the seasonal influenza A virus was not detected. Viral antigen and RNA were detected primarily in neuron- and astrocyte-like cells. Interferon responses to infection with HPAI H5N1 viruses were observed in a small population of bystander cells. Higher levels of cell death and proinflammatory cytokines and chemokines were observed in organoids inoculated with the historical HPAI H5N1 isolate. Conclusions:Clade 2.3.4.4b HPAI H5N1 viruses exhibit similar neurotropism compared to a historical clade 1 HPAI H5N1 virus. Lower levels of cell death and inflammatory cytokine production induced by clade 2.3.4.4b viruses may indicate reduced neuropathogenic potential of these viruses in humans.

The recent global pandemic illustrates the importance of understanding the host cellular infection processes of emerging zoonotic viruses. Nipah virus (NiV) is a deadly zoonotic biosafety level 4 encephalitic and respiratory paramyxovirus. Our knowledge of the molecular cell biology of NiV infection is extremely limited. This study identified changes in cellular components during NiV infection of human cells using a multi-platform, high-throughput transcriptomics, proteomics, lipidomics, and metabolomics approach. Remarkably, validation via multi-disciplinary approaches implicated viral glycoproteins in enriching mitochondria-associated proteins despite an overall decrease in protein translation. Our approach also allowed the mapping of significant fluctuations in the metabolism of glucose, lipids, and several amino acids, suggesting periodic changes in glycolysis and a transition to fatty acid oxidation and glutamine anaplerosis to support mitochondrial ATP synthesis. Notably, these analyses provide an atlas of cellular changes during NiV infections, which is helpful in designing therapeutics against the rapidly growing Henipavirus genus and related viral infections.

Nipah virus (NiV) is a highly pathogenic Paramyxovirus associated with outbreaks in Malaysia, Bangladesh, and India with high mortality rates. NiV infection causes fatal respiratory and neurological disease. The majority of survivors suffer from long-term neurological sequelae or late onset and relapsed encephalitis. The pathogenesis of neurological disease is complex and has not been able to be studied in current animal models as they are skewed towards the development of lethal respiratory disease rather than neurological disease. Although NiV neurological disease can be observed in animal models, there is currently no model where the majority of animals consistently develop neurological disease. Here, we developed a new Syrian hamster (Mesocricetus auratus) model to mimic neurological disease in humans. Hamsters were inoculated intracranially in the cerebellomedullary cistern with different doses of NiV, strain Malaysia. Intracranial NiV inoculation in the cerebellomedullary cistern resulted in a rapid progression towards severe neurological disease requiring euthanasia. High Nipah viral loads were detected in the brains, and NiV spread from the CNS to the lungs. Histopathologic examination of the brain showed ischemic necrosis, often accompanied by marked edema and hemorrhage. NiV antigen was detected primarily in meninges and cerebellum, but rarely observed in brain parenchyma. These histological lesions were different from the typical lesions observed in NiV-infected humans. Thus, despite the consistent development of neurological disease, intracranial inoculation does not result in a model representative of NiV neurological disease.

Zoonotic viruses with the ability to replicate in the human respiratory tract pose a threat to public health. Organoids, which are highly representative, multicellular models representing specific organs or tissues, can aid in our understanding of the pathogenesis, pathogenicity, transmissibility, and reservoir circulation dynamics of zoonotic viruses. Organoid studies can facilitate the rapid selection of antiviral therapies identification of potential reservoir species and intermediate hosts, and inform the selection of suitable laboratory animal models. We review the use of human- and animal-derived organoid models from multiple organs to investigate the threat of emerging zoonotic viruses that cause respiratory disease.

Nipah virus causes highly lethal disease, with case-fatality rates ranging from 40% to 100% in recognised outbreaks. No treatments or licensed vaccines are currently available for the prevention and control of Nipah virus infection. In 2019, WHO published an advanced draft of a research and development roadmap for accelerating development of medical countermeasures, including diagnostics, therapeutics, and vaccines, to enable effective and timely emergency response to Nipah virus outbreaks. This Personal View provides an update to the WHO roadmap by defining current research priorities for development of Nipah virus medical countermeasures, based primarily on literature published in the last 5 years and consensus opinion of 15 subject matter experts with broad experience in development of medical countermeasures for Nipah virus or experience in the epidemiology, ecology, or public health control of outbreaks of Nipah virus. The research priorities are organised into four main sections: cross-cutting issues (for those that apply to more than one category of medical countermeasures), diagnostics, therapeutics, and vaccines. The strategic goals and milestones identified in each section focus on key achievements that are needed over the next 6 years to ensure that the necessary tools are available for rapid response to future outbreaks of Nipah virus or related henipaviruses.

The highly pathogenic avian influenza (HPAI) A(H5N1) clade 2.3.4.4b viruses, responsible for the current outbreak in dairy cows in the United States, pose a significant animal and public health threat. In this study, we compared disease progression and pathology of three recent clade 2.3.4.4b isolates derived from a cow, mountain lion, and mink to a human HPAI A(H5N1) isolate from Vietnam in mice. Inoculation of C57BL/6J and BALB/c mice with all four HPAI A(H5N1) isolates resulted in comparable levels of virus replication in the lung inducing severe respiratory disease. C57BL/6J mice infected with the bovine isolate also developed high virus titers in the brain, resulting in a significant pro-inflammatory cytokine response and neurologic disease. Our findings suggest the recent bovine isolate possesses enhanced respiratory and neuroinvasive/neurovirulent properties causing fatal respiratory and neurologic disease in C57BL/6J mice. ### Competing Interest Statement The authors have declared no competing interest.

In recent years, the landscape of highly pathogenic avian influenza (HPAI) virus infections has shifted, as evidenced by an increase in infections among mammals. This includes the recent circulation of H5N1 in dairy cattle herds in the USA and a rise in associated human cases. In this study, we investigated differences in tissue tropism of two HPAI H5N1 strains, the isolate A/Vietnam/1203/2004 (VN1203) isolated from a fatal human case in 2004 and the bovine isolate A/Bovine/Ohio/B24osu-342/2024 (Bov342) isolated in 2024, in C57BL/6J mice. Infection with either HPAI H5N1 isolate was uniformly lethal in mice. However, tissue tropism differed significantly: while VN1203 replication was largely restricted to the respiratory tract, Bov342 successfully replicated in the respiratory tract as well as various regions of the brain. Bov342-challenged animals exhibited clinical signs consistent with central nervous system (CNS) infection, and infectious virus was detected in brain tissue. Correspondingly, cytokine profiles in the brain differed significantly between the isolates. Notably, in addition to abundant evidence of CNS infection in Bov342-challenged mice via immunohistochemistry, sporadic intranuclear and intracytoplasmic immunoreactivity was observed in other tissues in the head, including the choroid plexus, retina, and inner ear. This study demonstrates that while both HPAI H5N1 isolates are uniformly lethal in C57BL/6J mice upon aerosol exposure, significant differences exist in tissue tropism, with Bov342 resulting in respiratory disease as well as increased neurotropism and inflammation in the brain and nasal turbinates compared to VN1203, which predominantly induces respiratory disease. ### Competing Interest Statement The authors have declared no competing interest.

Influenza A(H5N1) virus has been identified in dairy herds and in the commercial milk supply. In this report, inactivation of the virus in milk by heating is studied.

Background Nipah virus is an emerging zoonotic virus that causes severe respiratory disease and meningoencephalitis. The pathophysiology of Nipah virus meningoencephalitis is poorly understood.Methods We have collected the brains of African green monkeys during multiple Nipah virus, Bangladesh studies, resulting in 14 brains with Nipah virus-associated lesions.Results The lesions seen in the brain of African green monkeys infected with Nipah virus, Bangladesh were very similar to those observed in humans with Nipah virus, Malaysia infection. We observed viral RNA and antigen within neurons and endothelial cells, within encephalitis foci and in uninflamed portions of the central nervous system (CNS). CD8+ T cells had a consistently high prevalence in CNS lesions. We developed a UNet model for quantifying and visualizing inflammation in the brain in a high-throughput and unbiased manner. While CD8+ T cells had a consistently high prevalence in CNS lesions, the model revealed that CD68+ cells were numerically the immune cell with the highest prevalence in the CNS of Nipah virus-infected animals.Conclusions Our study provides an in-depth analysis on Nipah virus infection in the brains of primates, and similarities between lesions in patients and the animals in our study validate this model. This is an in-depth study into the spectrum and distribution of CNS lesions in African green monkeys infected with Nipah virus. CNS lesions during the acute and convalescent stage were investigated, providing valuable insight into Nipah virus meningoencephalitis.