Abstract
BACKGROUND: Viral infections pose a significant challenge to the equine population, compromising welfare and causing substantial economic losses for the global equine industry. While numerous equine viral pathogens have been identified, many suspected viral infections remain undiagnosed. This highlights the need for further identification and characterization of viruses circulating within the equine population. In this study, we utilized viral metagenomics to investigate viruses present in serum samples and nasal swabs collected from horses in Sweden. The primary focus was on horses presenting with fever, although control horses were also included for comparison. RESULT: The viral metagenomic analysis identified several viruses in the investigated samples. Among nasal swabs, the majority of the viral reads were classified as various equine herpesvirues (EHVs), mainly EHV-2 and EHV-5. Other viruses in nasal swabs include but are not limited to EHV-4, Torque teno equus virus 1 (TTeqV1) and equine copiparvovirus (eqCopV). Both TTeqV1 and eqCopV were also detected in the serum samples together with equine circovirus and equine pegivirus. A number of the detected viruses were further genetically characterized and were shown to display high sequence similarity to viruses from the US and/or China. qPCR screening of a selected number of the detected viruses revealed a rather low detection rate (1.6%-9.4%) in individual horses. CONCLUSION: This study identified several viruses that circulate in the horse population in Sweden, some of which have not been previously detected in Sweden or Europe. Furthermore, the complete or nearly complete genomes of several of these viruses have been genetically characterized. These new data provide a valuable foundation for developing improved detection assays and conducting larger prevalence studies to assess the potential impact of these viruses on the equine population. Such efforts could ultimately contribute to enhanced equine welfare.