The Boundaries of Arboviruses: Complexities Revealed in Their Host Ranges, Virus-Host Interactions and Evolutionary Relationships
from: Arboviruses: Molecular Biology, Evolution and Control (Edited by: Nikos Vasilakis and Duane J. Gubler). Caister Academic Press, U.K. (2016) Pages: 219-268.
Reflecting the sharp increase in public health and veterinary problems caused by arboviruses in the past several decades, scientists worldwide have generated enormous amounts of data and publications about arboviruses and a variety of other related animal viruses currently not classified in this group of viruses on the basis of arbovirus definition. Upon a closer examination of the latter group of viruses, however, it has become clear that the definition of arbovirus, the tenets, and concepts on which arbovirology is established need to be re-evaluated for their ambiguity, absence of supporting evidence, inconsistency or difficulty of generalization, and an assortment of other problems in defining the boundaries between arboviruses and non-arboviruses. To understand the origins of those problematic issues, first, it is necessary to trace the early histories of virus-host interactions conducive to the evolution of biological transmission. Accordingly, viral associations with arthropods, vertebrates and even plants in both terrestrial and/or aquatic environments are examined. The emphases of the analysis are on the uniqueness of the biology of vectors, vertebrates, ecosystem, opportunity of virus-host contact, food chain, and the impacts of viral infection on hosts. The second foci of analysis concern the markers involved in the evolutionary process. Because virus-host interaction operating under particular ecological conditions is unique to each viral lineage, generalization of the markers among all arboviral lineages is difficult. Nevertheless, given rapidly accumulating useful information enriching the database, it is now possible to undertake such a study in at least a few arboviral lineages. In a study of flaviviruses, the history of host range shift, genome (or gene) length, and the motifs in the 3' UTR were found to be useful markers for elucidating the evolutionary history of the lineage. As byproducts of this review process, many problematic issues surfaced. They include definition and measurement of virulence, existence of vertebrate reservoir, non-viremic transmission, accuracy of molecular phylogeny without a support of empirical data, validity of in vitro experiments for the identification of genetic determinants of phenotypic shift, existence of the viruses which replicate in both arthropods and vertebrates (viruses with a biphylum host range) but without a need of biological transmission for survival, accuracy of host range of arboviruses and biological transmission in aquatic environments. Collectively, these issues and derived questions, coupled with the ambiguity of the boundaries of arboviruses, warrant an urgent re-assessment of the fundamentals of arbovirology read more ...