Biological Transmission of Arboviruses: Reexamination of and New Insights into Components, Mechanisms, and Unique Traits as Well as Their Evolutionary Trends

Abstract

SUMMARY Among animal viruses, arboviruses are unique in that they depend on arthropod vectors for transmission. Field research and laboratory investigations related to the three components of this unique mode of transmission, virus, vector, and vertebrate host, have produced an enormous amount of valuable information that may be found in numerous publications. However, despite many reviews on specific viruses, diseases, or interests, a systematic approach to organizing the available information on all facets of biological transmission and then to interpret it in the context of the evolutionary process has not been attempted before. Such an attempt in this review clearly demonstrates tremendous progress made worldwide to characterize the viruses, to comprehend disease transmission and pathogenesis, and to understand the biology of vectors and their role in transmission. The rapid progress in molecular biologic techniques also helped resolve many virologic puzzles and yielded highly valuable data hitherto unavailable, such as characterization of virus receptors, the genetic basis of vertebrate resistance to viral infection, and phylogenetic evidence of the history of host range shifts in arboviruses. However, glaring gaps in knowledge of many critical subjects, such as the mechanism of viral persistence and the existence of vertebrate reservoirs, are still evident. Furthermore, with the accumulated data, new questions were raised, such as evolutionary directions of virus virulence and of host range. Although many fundamental questions on the evolution of this unique mode of transmission remained unresolved in the absence of a fossil record, available observations for arboviruses and the information derived from studies in other fields of the biological sciences suggested convergent evolution as a plausible process. Overall, discussion of the diverse range of theories proposed and observations made by many investigators was found to be highly valuable for sorting out the possible mechanism(s) of the emergence of arboviral diseases.

Complete genome characterization of Rocio virus (Flavivirus: Flaviviridae), a Brazilian flavivirus isolated from a fatal case of encephalitis during an epidemic in São Paulo state

“…Numerous phylogenetic studies (Billoir et al, 2000;Cook & Holmes, 2005;Gould et al, 2003;Kuno et al, 1998Kuno et al, , 2005 have been conducted using sequences of individual genes and/or ORF to investigate the flavivirus genetic relationship. These studies generated basically two contrasting phylogenies, NS5 gene tree and NS3/ORF tree.…”

“…However, it should be noted that strain variation in the number of sites has been reported. Thus, in the E gene of SLEV, while the Argentine 66 has one, strain MSI-7 has two, but strain Tr 9464 has no glycosylation sites (Kuno & Chang, 2005;Vorndam et al, 1993). Regarding cysteine residues, as strictly required for stabilizing disulfide bridges in all mosquito-borne viruses, 12 residues were found in the ectodomain of E and in NS1 genes of ROCV.…”

Mode of transmission and the evolution of arbovirus virulence in mosquito vectors

“…When they have been investigated, factors such as initial viral dose (Cooper et al 2000;Mahmood et al 2004), virus strain (Scott & Lorenz 1998) or environmental quality (Patrican & DeFoliart 1985;Dohm et al 1991) did not significantly explain the extent of the fitness cost of infection. Thus, despite the importance of vector-virus relationships on arbovirus emergence and maintenance in nature (Kuno & Chang 2005;Weaver 2006) and the key role of vector fitness on vector-borne disease dynamics (Dye 1992;Kramer & Ebel 2003), the causes underlying variation in observed levels of arboviral virulence to vectors have not been elucidated. Here, we use a meta-analysis to disentangle the relative contributions of several biological and experimental factors to the effect of arbovirus infection on survival of their mosquito vectors.…”

Levantamento soroepidemiológico para arbovírus em macaco-prego-galego (Cebus flavius) de vida livre no estado da Paraíba e em macaco-prego (Cebus libidinosus) de cativeiro do nordeste do Brasil

“…Segundo Kuno & Chang (2005), o isolamento do vírus de animais suspeitos, a demonstração de viremia e a prevalência de anticorpos relativamente elevada nos animais capturados no campo são as principais informações utilizadas na identificação de reservatórios vertebrados para as arboviroses.…”