- Volume 106, Issue 12, 2025

Equine arteritis virus (EAV) is the causative agent of equine viral arteritis, a notifiable respiratory and reproductive disease of equids that causes significant losses to the equine industry. This study presents a comprehensive analysis of two EAV outbreaks in the UK in 2019, combining virus isolation, sequencing and phylogenetic analysis to provide a holistic understanding of EAV dynamics in these outbreaks. Genetic characterization revealed that all outbreak strains were similar to viruses detected in the UK and Europe from 2004 to 2011, belonging to phylogroup D and clustering in two groups as expected based on epidemiological profiling. Bayesian phylogenetic analysis indicated the direction of transmission. The 2019 EAV strains showed maximum variability in glycoprotein (GP) 3, followed by GP2, non-structural protein 2, GP4 and GP5, with one strain displaying a unique truncation in GP4 at position 149, a feature not previously identified in arteriviruses. Polymorphisms in the CXCL16 gene have been implicated in differential susceptibility to the establishment of long-term carrier states of EAV in stallions. Genotypic analysis of the CXCL16 gene revealed that one horse possessed the homozygous genotype associated with resistance to persistent infection. In contrast, the remaining four horses exhibited the heterozygous genotype, which has been linked to an increased risk of developing a long-term carrier state and contributing to ongoing viral transmission. All infected horses exhibited the presence of neutralizing antibodies in their serum. This study underscores the importance of early detection of silent infections to reduce the spread and prevent clinical outbreaks.

The 2013 Ebola virus (EBOV) outbreak was the largest in history. Despite recent advances in both vaccines and monoclonal antibody therapies, 12 years later, EBOV still poses a substantial threat. Previously, we published a ligand discovery pipeline combining in silico screening of compounds with a robust and rapid EBOV minigenome assay for early-stage inhibitor validation at Biological Safety Level 2. Here, we present the further use of this pipeline to identify three compounds that also inhibit EBOV minigenome transcription and replication. They are efficacious in the nM range, exhibited low cytotoxicity and were specific, with no effect on either a T7 RNA polymerase-driven firefly luciferase or a Bunyamwera virus minigenome. Furthermore, these small-molecule inhibitors exhibited the ability to block EBOV minigenome activity when applied after establishment of replication complexes, with implications for potential post-exposure EBOV treatment.

Influenza D virus (IDV), a new genus within the Orthomyxoviridae family, was initially detected in pigs and cattle. IDV is structurally similar to the influenza C virus (ICV). Influenza A, C and D viruses all have non-human maintenance hosts and likely circulate in several mammalian species. Camelids, as a reservoir for zoonotic viruses, were not extensively studied until the emergence of the Middle East respiratory syndrome coronavirus in 2012. Antibody responses to both ICV and IDV could be detected in dromedary camels from Kenya but not differentiated, owing to cross-reactivity. It was unclear whether these findings reflected a technical issue or suggested a role for camelids in ICV and IDV ecology. In the present study, therefore, alpacas (Vicugna pacos), a camelid species, were experimentally inoculated with ICV (C/Victoria/1/2011) or IDV (D/bovine/France/5920/2014) to assess susceptibility and assess the antibody response. We have demonstrated that alpacas can be experimentally infected with both ICV and IDV with subclinical infection of the upper respiratory tract, suggesting that virus transmission could potentially occur. These findings accord with previous serology results obtained for camelids and indicate a putative role for these species in ICV and IDV ecology.

During the summer of 2020, West Nile virus (WNV) caused an important outbreak in south-western Spain, with the highest impact on humans in the country up to that time, resulting in 77 clinical cases (including eight fatalities). Concurrently, equine WNV foci were reported within the same region. Meanwhile, WNV circulation was also detected in horses and birds in north-eastern Spain (Catalonia), although no human cases were notified. This striking difference in human case incidence between these two affected areas may be due to characteristics of the strains circulating in each site. One of these intrinsic viral strain factors that may account for these differences is the competence of avian reservoir hosts. A higher host competence leads to a higher viral spread in the enzootic cycle, consequently, increasing the risk of spillover to humans and horses. To assess differences in host competence, WNV strains circulating in both areas during the summer of 2020 were studied through in vivo inoculation of a transmission-competent avian species susceptible to WNV infection, the red-legged partridge, autochthonous to the Iberian Peninsula. The south-western strain SPA20-02, belonging to lineage 1, and the north-eastern strain AC924, belonging to lineage 2, were inoculated in parallel in red-legged partridges. The SPA20-02 strain exhibited higher and longer viraemias than the AC924 strain, resulting in a higher competence index for this avian species. The lower competence index of red-legged partridges for transmission of AC924 suggests that this strain exhibits a lower transmission capacity and, consequently, lower spread risk. These findings indicate that the lower severity of the 2020 outbreak in north-eastern Spain could, at least partially, be explained by the reduced transmission potential of the AC924 strain.

Hantaviruses are zoonotic, tri-segmented, negative-sense RNA viruses and a significant public health threat. Viral pathogenesis varies between host species, with rodent reservoir infection being asymptomatic and human infection resulting in severe, immune-mediated disease. Viral pathogenesis is highly dependent on virus replication efficiency since it affects the virus’s ability to evade detection and determines the magnitude of the host immune response. However, the molecular replication kinetics for hantaviruses remain poorly defined. Therefore, we developed a sense- and segment-specific quantitative real-time PCR assay and an SYBR-based RT-qPCR assay, allowing us to quantify both negative-sense genome levels and total viral RNA synthesis of the small (S), medium (M), and large (L) segments of Seoul virus (SEOV). We then measured total viral RNA and genome accumulation in reservoir rat endothelial cells (RLMVEC), non-reservoir human endothelial cells (HUVEC-C), and Vero E6 epithelial cells. We also measured the ratio of each segment released into the culture supernatant, approximating the relative packaging efficiency. We found that, while the magnitude of viral RNA differed, RNA replication kinetics were largely similar between reservoir and non-reservoir endothelial cells. However, replication and release kinetics differed between infection of endothelial and Vero cells. We also found that the S, M, and L segments were not equally abundant during viral infection or release but instead followed a trend of M>L>S. Overall, this study validates two RT-qPCR assays to measure SEOV RNA, details the accumulation and release of each viral segment and demonstrates the impact of host cell type on hantavirus replication.

Cutavirus (CuV), the newest human protoparvovirus (PPV), has gained attention due to its significant association with cutaneous T-cell lymphoma (CTCL) and its precursor, parapsoriasis, whereas the other human PPVs, bufavirus and tusavirus, show no such link. Given this association, it is important to investigate the prevalence of CuV DNA in other tissues, particularly those affected by malignancy or inflammation. This study assessed, by multiplex quantitative PCR, the genoprevalences of all three PPVs in 427 fresh-frozen intestinal biopsies from inflammatory bowel disease (IBD), colorectal cancer, adenomas or healthy mucosa of 185 individuals, as well as in 94 formalin-fixed paraffin-embedded (FFPE) biopsies from malignant and non-malignant breast conditions of 85 patients. The study also compared the DNA prevalences of human herpesvirus (HHV)-6A, -6B and -7 in the breast tissues. CuV mRNA was assayed with reverse-transcription PCR, and corresponding FFPE sections underwent in situ hybridization. CuV DNA was detected in intestinal IBD or healthy mucosa from 6/185 (3.2%) subjects, but no CuV mRNA or in situ signals were detected. In breast biopsies, HHV-6B and HHV-7 DNAs were present in 20.3 and 5.1%, respectively, while all PPVs and HHV-6A were absent. Overall, CuV was absent in all 70 cancer tissues, underscoring its association with CTCL. The low CuV DNA loads and prevalences in intestinal and breast morbidities, and lack of activity, suggest that CuV is unlikely to play a role in these malignancies or inflammatory conditions. In contrast, HHV-6B may be more relevant to breast pathology, even though it is also widely detected in healthy tissues. Nevertheless, our study provides insight into persistent DNA viruses implicated in cancer and highlights their occurrence across various disease manifestations, laying a foundation for future studies.

Since the 1990s, the Pacific oyster (Magallana gigas) has experienced repeated mortality events associated with Ostreid herpesvirus 1 (OsHV-1). Although the virus has been genomically characterised, its replication cycle and its interactions with the oyster immune system are still not well understood. In particular, little is known about the dynamics of OsHV-1 gene expression and the immune responses of haemocytes from oysters with varying susceptibility to the virus. While some studies have focused on the expression of specific viral and host genes in whole oysters, none have provided a comprehensive analysis of genome-wide expression across multiple post-infection time points in haemocytes.

The lack of oyster cell lines makes studying virus–host interactions in vitro challenging. However, haemocytes, the key immune cells circulating in haemolymph, can be maintained in vitro in the short term and represent a relevant model for analysing infection dynamics. In this study, haemocytes from two M. gigas batches, one highly susceptible and one less susceptible to OsHV-1, were infected in vitro. We tracked the viral and host transcriptomes over a 24-h period post-infection using high-throughput dual transcriptomics.

Our results provide a detailed overview of the OsHV-1 transcriptomic landscape in haemocytes from high- and low-susceptible M. gigas over time. In addition, weighted correlation network analysis of host gene expression provided insights into the haemocytes’ response to infection and highlighted batch-specific immune responses. This comprehensive transcriptomic study is the first to describe virus–host interactions across multiple stages of infection in haemocytes from Pacific oysters, showing contrasted survival when exposed to OsHV-1.

Marek’s disease virus (MDV) is an alphaherpesvirus responsible for the development of T-cell lymphoma in chickens. Despite the identification of several pro-oncogenic viral molecules encoded by MDV, the processes leading to tumourigenesis remain poorly understood. Extracellular vesicles (EVs) are important mediators of intercellular communication, carrying bioactive molecules that can elicit profound physiological changes in recipient cells. Tumour cells can release significant amounts of EVs, which influence tumour development and growth, metastatic processes and resistance to cancer therapies. These EVs favour cancer cells to evade the immune response, particularly by establishing an immunosuppressive microenvironment. Here, we investigated whether EVs produced by MDV-transformed T lymphocytes affect the proliferation of avian immune cells, a determining feature in neoplastic processes. EVs were purified from an MDV-transformed cell line cultured in vitro. Using a proteomic approach, we confirmed the presence of specific markers and identified a panel of cellular proteins enriched in these EVs. Notably, no viral proteins were detected in the purified EVs. We also demonstrated that EVs are rapidly internalized by recipient chicken cells. Moreover, these EVs can induce a decrease in primary chicken B-cell proliferation, while promoting primary chicken T-cell proliferation. Our findings suggest that EVs released by MDV-transformed cells may contribute to immunosuppression and potentially facilitate lymphoma progression by enhancing T-cell proliferation.