ReviewPresent and future arboviral threats
Section snippets
Introduction to the arboviruses
Arthropod-borne viruses (arboviruses) are transmitted biologically among vertebrate hosts by hematophagous (blood feeding) arthropod vectors such as mosquitoes and other biting flies, and ticks. Being, by definition, biologically transmitted, arboviruses must replicate in the arthropod vector prior to transmission, as opposed to being mechanically transmitted, without replication in the vector, through contaminated mouthparts (Weaver, 1997). Biological transmission can be vertical, involving
Factors associated with arbovirus emergence or invasion
For arboviral amplification to progress rapidly to epidemic levels, competent vector and vertebrate host populations must intersect repeatedly within a permissive environment. This focus or nidus of transmission may be temporally and/or spatially constrained by host or virus ecology, and may vary in complexity depending upon virus epidemiology. Zoonoses exploiting complex rural or suburban ecosystems may have multiple vectors and infect a variety of vertebrate host species, whereas
Distribution and health significance
West Nile virus (WNV) is positioned taxonomically within the Japanese encephalitis virus (JEV) serocomplex in the genus Flavivirus. It is maintained and amplified in nature within an enzootic transmission cycle among passeriform birds and Culex mosquitoes, with outbreaks caused by tangential or spillover transmission to equids and humans, ‘dead-end’ hosts that produce viremias inadequate for mosquito infection. WNV is distributed circumglobally, with two main genetic lineages: Lineage 1 is
Distribution and health significance
Dengue viruses comprise four related serotypes that share common transmission cycles (Fig. 5). They are flaviviruses (Flaviviridae: Flavivirus) closely related to JEV and WNV described above; however, unlike all other flaviviruses, DENVs that cause most human disease are not zoonoses, but exclusively utilize humans as reservoir and amplification hosts. Also unlike most arboviruses, they rely on transmission by mosquito vectors that live in close association with people; Ae. (Stegomyia) aegypti
Examples of other arboviruses with the potential for urban emergence
There are many known and probably even more unknown arboviruses with the potential for epidemic emergence, especially as climate change and urbanization enhance opportunities for spread and interhuman transmission. We include here a few of many examples of each emergence.
Conclusions
Arboviruses have a well-documented history of emergence through several mechanisms, including geographic expansion, often mediated through human transportation, and enhanced amplification in peridomestic commensal and domesticated animals leading to spillover to humans. Both of these mechanisms threaten to increase in the future due to increased human travel and global commerce as well as deforestation and tropical human population growth. Global warming also has the potential to increase the
Acknowledgments
The authors’ research is supported by NIH grants AI069145, AI25489 and AI071192 (SCW) and AI055607 (WKR), NASA grant 05-DEC05-S2-0016 (WKR) and CDC grant U01 EH000418-01 (WKR).
References (201)
- et al.
Arthropod-borne virus antibodies in sera of residents of Kainji Lake Basin, Nigeria 1980
Trans. R. Soc. Trop. Med. Hyg.
(1983) - et al.
Culicoides and the emergence of bluetongue virus in northern Europe
Trends Microbiol.
(2009) - et al.
Zika virus. I. Isolations and serological specificity
Trans. R. Soc. Trop. Med. Hyg.
(1952) - et al.
Preliminary observations on transplacental infection of bluetongue virus in sheep—a possible overwintering mechanism
Res. Vet. Sci.
(1979) - et al.
Japanese encephalitis in Nepal
Lancet
(1983) - et al.
A wind density model to quantify the airborne spread of Culicoides species during north-western Europe bluetongue epidemic, 2006
Prev. Vet. Med.
(2008) - et al.
The Rift Valley fever epizootic in Egypt 1977–1978. 2. Ecological and entomological studies
Trans. R. Soc. Trop. Med. Hyg.
(1979) - et al.
Effect of dengue-1 antibodies on American dengue-2 viral infection and dengue haemorrhagic fever
Lancet
(2002) - et al.
Complete genome sequences and phylogenetic analysis of West Nile virus strains isolated from the United States, Europe, and the Middle East
Virology
(2002) - Anon., 2008. Outbreak news. Yellow fever, Paraguay. Wkly. Epidemiol. Rec. 83,...