From ontogenesis to homeostasis, the phenotypes of complex organisms are shaped by the bidirectional interactions between the host organisms and their associated microbiota. Current technology can reveal many such interactions by combining multi-omic data from both hosts and microbes. However, exploring the full extent of these interactions requires careful consideration of study design for the efficient generation and optimal integration of data derived from (meta)genomics, (meta)transcriptomics, (meta)proteomics, and (meta)metabolomics. In this perspective, we introduce the holo-omic approach that incorporates multi-omic data from both host and microbiota domains to untangle the interplay between the two. We revisit the recent literature on biomolecular host-microbe interactions and discuss the implementation and current limitations of the holo-omic approach. We anticipate that the application of this approach can contribute to opening new research avenues and discoveries in biomedicine, biotechnology, agricultural and aquacultural sciences, nature conservation, as well as basic ecological and evolutionary research.

The European 2025/26 influenza season is dominated by the influenza A(H3N2) virus, with most sequenced viruses belonging to subclade K, genetically drifted from the vaccine virus, raising concerns around vaccine effectiveness (VE). Despite this, VE estimates from nine European studies (19 countries) indicate all-age influenza A VE of 25–45% for outpatient and hospital settings combined, similar to other seasons, with highest estimates among children (47–72%). Vaccination should be encouraged and complemented by other infection prevention and control measures.

As metagenomic studies continue to increase in size and complexity, they are often required to incorporate data from geographically isolated locations or longitudinal time samples. This represents a technical challenge, given that many of the commonly used methods used for sample collection, storage, and DNA extraction are sensitive to differences related to the time, storage and chemistry involved. FTA cards have been previously proposed as a simple, reliable and cost-efficient method for the preservation of animal faecal microbiomes. In this study, we report a simplified extraction methodology for recovering microbiome DNA from faeces stored on FTA cards and compare its performance to a common alternative means of characterising such microbiomes; namely, immediate freezing of the faeces followed by DNA extraction using the Qiagen PowerSoil DNA isolation kit. Our results show that overall the application of our simplified DNA extraction methodology yields microbial community results that have higher diversity and an expanded core microbiome than that found using the PowerSoil methodology. This suggests that the FTA card extraction method presented here is a viable alternative for metagenomic studies using faecal material when traditional freeze-based storage methods are not feasible.

Successfully adapting to a feral lifestyle with different access to food, shelter and other resources requires rapid physiological and behavioural changes, which could potentially be facilitated by gut microbiota plasticity. To investigate whether alterations in gut microbiota support this transition to a feral lifestyle, we analysed the gut microbiomes of domestic and feral cats from six geographically diverse locations using genome‐resolved metagenomics. By reconstructing 229 non‐redundant metagenome‐assembled genomes from 92 cats, we identified a typical carnivore microbiome structure, with notable diversity and taxonomic differences across regions. While overall diversity metrics did not differ significantly between domestic and feral cats, hierarchical modelling of species communities, accounting for geographic and sex covariates, revealed significantly larger microbial functional capacities among feral cats. The increased capacity for amino acid and lipid degradation corresponds to feral cats' dietary reliance on crude protein and fat. A second modelling analysis, using behavioural phenotype as the main predictor, unveiled a positive association between microbial production of short‐chain fatty acids, neurotransmitters and vitamins and cat aggressiveness, suggesting that gut microbes might contribute to heightened aggression and elusiveness observed in feral cats. Functional microbiome shifts may therefore play a significant role in the development of physiological and behavioural traits advantageous for a feral lifestyle, a hypothesis that warrants validation through microbiota manipulation experiments.

BACKGROUND: The Danish respiratory virus sentinel surveillance system has monitored influenza-like illness and influenza virus activity for over 30 years. During the last decade, additional virus groups were added. In 2021, the system was updated to include SARS-CoV-2, collect detailed symptomatic data, and transitioned to year-round surveillance. AIM: To explore the first two seasons of year-round respiratory virus surveillance and the first symptomatic data collected in the Danish primary care sentinel surveillance system. METHODS: In 2021/22 and 2022/23 seasons, 156 and 147 participating general practitioners, respectively, reported influenza-like illness consultation rates, collected symptomatic data and swabbed patient volunteers. Swabs were sent to Statens Serum Institut for multiplex PCR analysis, with additional characterisation using high-throughput sequencing or type-specific PCR assays for viruses such as influenza, SARS-CoV-2 and respiratory syncytial virus (RSV). RESULTS: During the two seasons, 4,391 and 6,034 swabs, respectively, were collected and analysed. Year-round surveillance detected an unusually early wave of RSV during 2022/23. While present in nearly all weeks, SARS-CoV-2 showed waves with increased detection. Year-round surveillance also highlighted consistent patterns, such as continuous presence of entero-/rhinoviruses and endemic coronaviruses, as well as parainfluenza virus appearing after influenza virus. Symptom data showed differences by both sex and virus type, e.g. headaches were more commonly reported by women with RSV. CONCLUSIONS: Our findings highlight the value of year-round respiratory virus surveillance in identifying both atypical virus activity and consistent patterns outside the winter season. Symptom data suggest the need for further research into sex-specific symptom patterns.

In week 33, 2025, the integrated respiratory virus surveillance at Statens Serum Institut, Denmark, detected an atypical sixfold increase in influenza A(H1N1)pdm09 cases. Rapid sequencing of viruses collected in week 33 identified a highly related cluster of 17 cases. Telephone interviews with patients belonging to this cluster revealed that they all had attended a large open-air music festival. This is the first time an influenza outbreak has been detected during the summer in Denmark related to a large gathering.