The recent global (re)emergence of arthropod-borne viruses (arboviruses), such as chikungunya and Zika virus, was widely reported in the media as though it was a new phenomenon. This is not the case. Arboviruses and other human microbial pathogens have been (re)emerging for centuries. The major difference today is that arbovirus emergence and dispersion are more rapid and geographically extensive, largely due to intensive growth of global transportation systems, arthropod adaptation to increasing urbanisation, our failure to contain mosquito population density increases and land perturbation. Here we select examples of (re)emerging pathogenic arboviruses and explain the reasons for their emergence and different patterns of dispersal, focusing particularly on the mosquito vectors which are important determinants of arbovirus emergence. We also attempt to identify arboviruses likely to (re)emerge in the future.

On the basis of population genomic and phylogeographic analyses of 1669 Mycobacterium tuberculosis lineage 4 (L4) genomes, we find that dispersal of L4 has been completely dominated by historical migrations out of Europe. We demonstrate an intimate temporal relationship between European colonial expansion into Africa and the Americas and the spread of L4 tuberculosis (TB). Markedly, in the age of antibiotics, mutations conferring antimicrobial resistance overwhelmingly emerged locally (at the level of nations), with minimal cross-border transmission of resistance. The latter finding was found to reflect the relatively recent emergence of these mutations, as a similar degree of local restriction was observed for susceptible variants emerging on comparable time scales. The restricted international transmission of drug-resistant TB suggests that containment efforts at the level of individual countries could be successful.

The unexpected emergence of Zika virus (ZIKV) in the Pacific Islands and Latin America and its association with congenital Zika virus syndrome (CZVS) (which includes microcephaly) and Guillain-Barré syndrome (GBS) have stimulated wide-ranging research. High densities of susceptible Aedes spp., immunologically naive human populations, global population growth with increased urbanization, and escalation of global transportation of humans and commercial goods carrying vectors and ZIKV undoubtedly enhanced the emergence of ZIKV. However, flavivirus mutations accumulate with time, increasing the likelihood that genetic viral differences are determinants of change in viral phenotype. Based on comparative ZIKV complete genome phylogenetic analyses and temporal estimates, we identify amino acid substitutions that may be associated with increased viral epidemicity, CZVS, and GBS. Reverse genetics, vector competence, and seroepidemiological studies will test our hypothesis that these amino acid substitutions are determinants of epidemic and neurotropic ZIKV emergence.

RNA viruses are abundant infectious agents and present in all domains of life. Arthropods, including ticks, are well known as vectors of many viruses of concern for human and animal health. Despite their obvious importance, the extent and structure of viral diversity in ticks is still poorly understood, particularly in Europe. Using a bulk RNA-sequencing approach that captures the complete transcriptome, we analysed the virome of the most common tick in Europe – Ixodes ricinus. In total, RNA sequencing was performed on six libraries consisting of 33 I. ricinus nymphs and adults sampled in Norway. Despite the small number of animals surveyed, our virus identification pipeline revealed nine diverse and novel viral species, phylogenetically positioned within four different viral groups – bunyaviruses, luteoviruses, mononegavirales and partitiviruses – and sometimes characterized by extensive genetic diversity including a potentially novel genus of bunyaviruses. This work sheds new light on the virus diversity in I. ricinus, expands our knowledge of potential host/vector-associations and tick-transmitted viruses within several viral groups, and pushes the latitudinal limit where it is likely to find tick-associated viruses. Notably, our phylogenetic analysis revealed the presence of tick-specific virus clades that span multiple continents, highlighting the role of ticks as important virus reservoirs.