The hepatitis C virus (HCV) is a major human pathogen. Genetically related viruses in animals suggest a zoonotic origin of HCV. The closest relative of HCV is found in horses (termed equine hepacivirus [EqHV]). However, low EqHV genetic diversity implies relatively recent acquisition of EqHV by horses, making a derivation of HCV from EqHV unlikely. To unravel the EqHV evolutionary history within equid sister species, we analyzed 829 donkeys and 53 mules sampled in nine European, Asian, African, and American countries by molecular and serologic tools for EqHV infection. Antibodies were found in 278 animals (31.5%), and viral RNA was found in 3 animals (0.3%), all of which were simultaneously seropositive. A low RNA prevalence in spite of high seroprevalence suggests a predominance of acute infection, a possible difference from the mostly chronic hepacivirus infection pattern seen in horses and humans. Limitation of transmission due to short courses of infection may explain the existence of entirely seronegative groups of animals. Donkey and horse EqHV strains were paraphyletic and 97.5 to 98.2% identical in their translated polyprotein sequences, making virus/host cospeciation unlikely. Evolutionary reconstructions supported host switches of EqHV between horses and donkeys without the involvement of adaptive evolution. Global admixture of donkey and horse hepaciviruses was compatible with anthropogenic alterations of EqHV ecology. In summary, our findings do not support EqHV as the origin of the significantly more diversified HCV. Identification of a host system with predominantly

BackgroundIn the past decade, many new paramyxoviruses that do not belong to any of the seven established genera in the family Paramyxoviridae have been discovered. Amongst them are J-virus (JPV), Beilong virus (BeiPV) and Tailam virus (TlmPV), three paramyxovirus species found in rodents. Based on their similarities, it has been suggested that these viruses should compose a new genus, tentatively called ‘Jeilongvirus’.ResultsHere we present the complete genomes of three newly discovered paramyxoviruses, one found in a bank vole (Myodes glareolus) from Slovenia and two in a single, co-infected Rungwe brush-furred rat (Lophuromys machangui) from Mozambique, that represent three new, separate species within the putative genus ‘Jeilongvirus’. The genome organization of these viruses is similar to other paramyxoviruses, but like JPV, BeiPV and TlmPV, they possess an additional open reading frame, encoding a transmembrane protein, that is located between the F and G genes. As is the case for all Jeilongviruses, the G genes of the viruses described here are unusually large, and their encoded proteins are characterized by a remarkable amino acid composition pattern that is not seen in other paramyxoviruses, but resembles certain motifs found in Orthopneumovirus G proteins.ConclusionsThe phylogenetic clustering of JPV, BeiPV and TlmPV with the viruses described here, as well as their shared features that set them apart from other paramyxoviruses, provide additional support for the recognition of the genus ‘Jeilongvirus’.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4995-0) contains supplementary material, which is available to authorized users.

The need to estimate divergence times in evolutionary histories in the presence of various sources of substitution rate variation has stimulated a rich development of relaxed molecular clock models. Viral evolutionary studies frequently adopt an uncorrelated clock model as a generic relaxed molecular clock process, but this may impose considerable estimation bias if discrete rate variation exists among clades or lineages. For HIV-1 group M, rate variation among subtypes has been shown to result in inconsistencies in time to the most recent common ancestor estimation. Although this calls into question the adequacy of available molecular dating methods, no solution to this problem has been offered so far. Here, we investigate the use of mixed effects molecular clock models, which combine both fixed and random effects in the evolutionary rate, to estimate divergence times. Using simulation, we demonstrate that this model outperforms existing molecular clock models in a Bayesian framework for estimating time-measured phylogenies in the presence of mixed sources of rate variation, while also maintaining good performance in simpler scenarios. By analysing a comprehensive HIV-1 group M complete genome data set we confirm considerable rate variation among subtypes that is not adequately modelled by uncorrelated relaxed clock models. The mixed effects clock model can accommodate this rate variation and results in a time to the most recent common ancestor of HIV-1 group M of 1920 (1915–25), which is only slightly earlier than the uncorrelated relaxed clock estimate for the same data set. The use of complete genome data appears to have a more profound impact than the molecular clock model because it reduces the credible intervals by 50 per cent relative to similar estimates based on short envelope gene sequences.