Nipah virus (NiV), a biosafety level 4 agent, was first identified in human clinical cases during an outbreak in 1998 in Malaysia and Singapore. While flying foxes are the primary host and viral vector, the infection is associated with a severe clinical presentation in humans, resulting in a high mortality rate. Therefore, NiV is considered a virus with an elevated epidemic potential which is further underscored by its recent emergence (September 2023) as an outbreak in India. Given the situation, it is paramount to understand the molecular dynamics of the virus to shed more light on its evolution and prevent potential future outbreaks. In this study, we conducted Bayesian phylogenetic analysis on all available NiV complete genomes, including partial N-gene NiV sequences (≥1000 bp) in public databases since the first human case, registered in 1998. We observed the distribution of genomes into three main clades corresponding to the genotypes Malaysia, Bangladesh and India, with the Malaysian clade being the oldest in evolutionary terms. The Bayesian skyline plot showed a recent increase in the viral population size since 2019. Protein analysis showed the presence of specific protein families (Hendra_C) in bats that might keep the infection in an asymptomatic state in bats, which also serve as viral vectors. Our results further indicate a shortage of complete NiV genomes, which would be instrumental in gaining a better understanding of NiV’s molecular evolution and preventing future outbreaks. Our investigation also underscores the critical need to strengthen genomic surveillance based on complete NiV genomes that will aid thorough genetic characterization of the circulating NiV strains and the phylogenetic relationships between the henipaviruses. This approach will better prepare us to tackle the challenges posed by the NiV virus and other emerging viruses.

The emergence of SARS-CoV-2 and the subsequent pandemic have prompted extensive diagnostic and clinical efforts to mitigate viral spread. However, these strategies have largely overlooked the presence of other respiratory viruses. Acute respiratory diseases in pediatric patients can be caused by a diverse range of viral agents, and metagenomics represents a powerful tool for their characterization. This study aimed to investigate the viral abundance in pediatric patients with acute respiratory symptoms who tested negative for SARS-CoV-2 during the Omicron pandemic wave. To achieve this, viral metagenomics and next-generation sequencing were employed on 96 nasopharyngeal swab samples, which were organized into 12 pools, with each pool consisting of eight individual samples. Metagenomic analysis revealed that the most prevalent viruses associated with acute disease in pediatric patients were respiratory syncytial virus (detected in all pools) and enteroviruses, which are known to cause significant morbidity and mortality in children. Additionally, clinically significant viruses such as mumps orthorubulavirus, human metapneumovirus, influenza A, and a wide array of human herpesviruses (1, 3–7) were identified. These findings highlight the extensive potential of viral metagenomics in identifying viruses other than SARS-CoV-2 that contribute to acute infections in children. Consequently, this methodology should garner clinical attention in terms of differential diagnosis and the development of public policies to address such conditions in the global pediatric population.

Acute respiratory infections (ARIs) remain a leading cause of global morbidity and mortality, disproportionately affecting vulnerable populations such as children, the elderly, and immunocompromised individuals. Despite the availability of traditional diagnostic tools, including viral culture and highly elaborated PCR respiratory panels, many cases of ARI remain without an identified etiological agent. This is due to the vast diversity of viral agents that can be involved in cases of ARI, which represents a major limitation of the targeted diagnosis. In this context, viral metagenomics has emerged as a powerful, unbiased approach for detecting both known and novel pathogens directly from clinical samples. This review highlights the application of metagenomic next-generation sequencing for the investigation of etiological causes of ARIs, emphasizing its relevance in complex cases—particularly among immunocompromised patients—where standard methods might fail. We highlight the main viruses involved in respiratory infections, the strengths and limitations of metagenomic next-generation sequencing approaches, their role in genomic surveillance of respiratory viruses, and their potential to build public health responses to potentially emerging respiratory threats. Ultimately, integrating viral metagenomics into clinical and surveillance frameworks could enhance the early detection and control of respiratory viral diseases worldwide.

Fulminant hepatitis is a severe clinical disease characterized by a marked decline in liver function and encephalopathy. In a previous survey, using metagenomics in a group of 27 patients with this clinical condition, we observed an expressive quantity of reads of the Human pegivirus-1 (HPgV-1). Therefore, the objective of this study was to evaluate the frequency, molecular features, and HPgV-1 circulating genotypes in patients with fulminant hepatitis. After testing the collected plasma samples, we discovered twelve samples (44.4%) that were positive for HPgV-1 RNA (using both real-time and nested PCR). The positive samples presented a mean cycle threshold (Ct) of 28.5 (±7.3). Genotyping assignments revealed that all HPgV-1 positive samples belonged to the HPgV-1 genotype 2 (both subgenotypes 2A and 2B were identified). Although HPgV-1 is considered a commensal virus, little is known regarding its prevalence and genotypes in cases of fulminant hepatitis. More research is needed to understand whether HPgV-1 can be implicated in clinical disorders and infectious diseases.

Viral hemorrhagic fever poses a significant public health challenge due to its severe clinical presentation and high mortality rate. The diagnostic process is hindered by similarity of symptoms across different diseases and the broad spectrum of pathogens that can cause hemorrhagic fever. In this study, we applied viral metagenomic analysis to 43 serum samples collected by the Public Health Laboratory (Fundação Ezequiel Dias, FUNED) in Minas Gerais State, Brazil, from patients diagnosed with hemorrhagic fever who had tested negative for the standard local hemorrhagic disease testing panel. This panel includes tests for Dengue virus (DENV) IgM, Zika virus IgM, Chikungunya virus IgM, yellow fever IgM, Hantavirus IgM, Rickettsia rickettsii IgM/IgG, and Leptospira interrogans IgM, in addition to respective molecular tests for these infectious agents. The samples were grouped into 18 pools according to geographic origin and analyzed through next-generation sequencing on the NextSeq 2000 platform. Bioinformatic analysis revealed a prevalent occurrence of commensal viruses across all pools, but, notably, a significant number of reads corresponding to the DENV serotype 2 were identified in one specific pool. Further verification via real-time PCR confirmed the presence of DENV-2 RNA in an index case involving an oncology patient with hemorrhagic fever who had initially tested negative for anti-DENV IgM antibodies, thereby excluding this sample from initial molecular testing. The complete DENV-2 genome isolated from this patient was taxonomically classified within the cosmopolitan genotype that was recently introduced into Brazil. These findings highlight the critical role of considering the patient’s clinical condition when deciding upon the most appropriate testing procedures. Additionally, this study showcases the potential of viral metagenomics in pinpointing the viral agents behind hemorrhagic diseases. Future research is needed to assess the practicality of incorporating metagenomics into standard viral diagnostic protocols.

Viral infections are one of the most important causes of morbidity and mortality among patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT). Immunosuppression may lead to the reactivation of latent viruses or the acquisition of new infections, resulting in severe clinical outcomes. The early detection of viral reactivations is crucial for effective patient management and post-transplant care. In this study, we employed next-generation metagenomics to assess changes in viral abundance and detect clinically significant viruses in allogeneic HSCT patients. A total of 20 patients from the Transplant Unit of the University Hospital of the Faculty of Medicine of Ribeirão Preto, University of São Paulo were included, with plasma samples collected at three time points: D + 0 (pre-transplantation), D + 30 (30 days post-transplantation), and D + 100 (~100 days post-transplantation). A higher presence of clinically relevant viruses, such as the cytomegalovirus (CMV), the Epstein-Barr virus (EBV) and adenoviruses, were predominantly detected at D + 30. The diversity of commensal viruses, primarily anelloviruses, increased gradually, with the highest abundance and variability detected at D + 100. Viruses with clinical importance for HSCT, including CMV, adenovirus and EBV, were confirmed and characterized at the molecular level, showing generally high cycle threshold values. Our findings demonstrate a rise in anellovirus abundance following allogeneic HSCT, with the highest levels observed at D + 100. Notably, D + 30 was identified as a critical time point for the reactivation of clinically significant viruses. This study underscores the potential of metagenomics in the identification of clinically relevant viruses and highlights the importance of monitoring latent viruses in immunocompromised populations, including allogeneic HSCT patients.