The passive protection afforded by the colostrum from cattle that were vaccinated prepartum with an inactivated combination vaccine against the bovine respiratory syncytial virus (BRSV) was evaluated after an experimental challenge of calves. Pregnant cows without or with a low ELISA and neutralizing BRSV antibody titers were twice vaccinated or not vaccinated, the last immunization being at one month prior to calving. Vaccination was followed by a rapid increase in BRSV antibody titers after the second immunization. Twenty-eightnewborn calves were fed during the 6 h following birth, with 4 L of colostrum sourced from vaccinated cows (14 vaccine calves) or non-vaccinated cows (14 control calves) and were challenged with BRSV at 21 days of age. We showed that maternal immunity to BRSV provides a significant reduction in the clinical signs of BRSV in calves, especially for severe clinical forms. This protection was correlated with reduced BRSV detection in the lower respiratory tract but not in nasal swabs, indicating an absence of protection against BRSV nasal excretion. Finally, transcriptomic assays in bronchoalveolar lavages showed no statistical differences between groups for chemokine and cytokine mRNA transcriptions, with the exception of the overexpression of IL-9 at days 6 and 10 post-challenge, and a severe downregulation of CXCL-1 at day 3 post-challenge, in the vaccine group.

The exceptional impact of the COVID-19 pandemic has stimulated an intense search for antiviral molecules. Host-targeted antiviral molecules have the potential of presenting broad-spectrum antiviral activity and are also considered as less likely to select for resistant viruses. In this study, we investigated the antiviral activity exerted by AM-001, a specific pharmacological inhibitor of EPAC1, a host exchange protein directly activated by cyclic AMP (cAMP). The cAMP-sensitive protein, EPAC1 regulates various physiological and pathological processes but its role in SARS-CoV-2 and influenza A virus infection has not yet been studied. Here, we provide evidence that the EPAC1 specific inhibitor AM-001 exerts potent antiviral activity against SARS-CoV-2 in the human lung Calu-3 cell line and the African green monkey Vero cell line. We observed a concentration-dependent inhibition of SARS-CoV-2 infectious viral particles and viral RNA release in the supernatants of AM-001 treated cells that was not associated with a significant impact on cellular viability. Furthermore, we identified AM-001 as an inhibitor of influenza A virus in Calu-3 cells. Altogether these results identify EPAC1 inhibition as a promising therapeutic target against viral infections.

Immature feathers are known replication sites for high pathogenicity avian influenza viruses (HPAIVs) in poultry. However, it is unclear whether feathers play an active role in viral transmission. This study aims to investigate the contribution of the feather epithelium to the dissemination of clade 2.3.4.4b goose/Guangdong/1996 lineage H5 HPAIVs in the environment, based on natural and experimental infections of domestic ducks. During the 2016-22 outbreaks, H5 HPAIVs exhibited persistent and marked feather epitheliotropism in naturally infected commercial ducks. Infection of feathers resulted in epithelial necrosis, disruption, and the production and release of infectious virions. Viral and feather antigens colocalized in dust samples obtained from poultry barns housing naturally infected birds. In summary, the feather epithelium contributes to viral replication, and it is a likely source of environmental infectious material. This underestimated excretion route could greatly impact the ecology of HPAIVs, facilitating airborne and preening-related infections within a flock, and promoting prolonged viral infectivity and long-distance viral transmission between poultry farms. Abstract Figure:

While rapid death is the usual outcome of high pathogenicity avian influenza virus (HPAIV) infection in gallinaceous poultry, HPAIV-infected ducks usually present milder clinical signs and shed virus for a prolonged time. The difference in disease severity has been linked to a more rapid type I IFN immune response and reduced proinflammatory cytokine expression in ducks compared to chickens. To investigate the role of the early antiviral innate immune response in controlling viral replication in ducks, we evaluated the effects of ruxolitinib, a Janus kinase–signal transducer and activator of transcription (JAK–STAT) pathway inhibitor known to dampen IFN signalling in mammals. We first optimized a treatment protocol in 2-week-old ducklings and showed that repeated intracoelomic injections of ruxolitinib significantly decreased IFN-stimulated gene (ISG) mRNA levels in the lung, while oral administration was ineffective. In subsequent infection experiments with an H5N9 HPAIV strain, ruxolitinib treatment led to an earlier peak of viral shedding and increased viral RNA levels in respiratory tissues, which however was not associated with increased expression of clinical signs. Analysis of host immune gene expression in the respiratory tract confirmed a transient suppression of ISG expression coincident with ruxolitinib treatment, followed by a recovery once treatment was ceased. This work provides the first demonstration of the effectiveness of ruxolitinib at inhibiting the antiviral innate immune response in birds, causing increased levels of virus replication when administered to HPAIV-infected ducks.

Recognition of viral double-stranded RNA (dsRNA) is a central trigger of innate antiviral immunity, yet the role of RNA length in shaping immune sensing across species remains poorly defined. Here, we identify RNA length as a key determinant of innate immune activation and demonstrate that this parameter is differentially tuned across vertebrate hosts. Using defined dsRNA molecules, we compared immune responses in human, duck, and chicken cells. Short 5′-triphosphorylated dsRNAs, including influenza-derived mini viral RNAs, robustly activated antiviral responses in human and duck cells but failed to do so in chicken cells. In contrast, longer dsRNAs induced immune activation across all species, revealing a species-specific threshold for dsRNA recognition. Mechanistically, this threshold is defined by differential engagement of RNA sensors. In human cells, sensing of short and intermediate dsRNA is strictly dependent on RIG-I, whereas in chicken cells, which lack RIG-I, MDA5 mediates dsRNA recognition and imposes a higher length requirement for activation. Consistent with this, duck cells, which retain RIG-I, respond to short dsRNA similarly to human cells. These differences in dsRNA sensing are accompanied by differential activation of downstream antiviral pathways, including PKR-dependent translational control and OAS/RNase L activation. Together, our findings identify RNA length as a fundamental parameter governing innate immune recognition and reveal that species-specific usage of RNA sensors constrains antiviral sensing, with implications for host susceptibility and virus-host interactions.