%0 Journal Article
%T The Pathogenesis of Alphaviruses
%A Gregory J. Atkins
%J ISRN Virology
%D 2013
%R 10.5402/2013/861912
%X Alphaviruses are enveloped single-stranded positive sense RNA viruses of the family Togaviridae. The genus alphavirus contains nine viruses, which are of medical, theoretical, or economic importance, and which will be considered. Sindbis virus (SINV) and Semliki Forest (SFV), although of some medical importance, have largely been studied as models of viral pathogenicity. In mice, SINV and SFV infect neurons in the central nervous system and virulent strains induce lethal encephalitis, whereas avirulent strains of SFV induce demyelination. SFV infects the developing foetus and can be teratogenic. Venezuelan Equine Encephalitis virus, Eastern Equine Encephalitis virus, and Western Equine Encephalitis virus can induce encephalitis in horses and humans. They are prevalent in the Americas and are mosquito transmitted. Ross River virus, Chikungunya virus (CHIKV), and O¡¯nyong-nyong virus (ONNV) are prevalent in Australasia, Africa and Asia, and Africa, respectively. ONNV virus is transmitted by Anopheles mosquitoes, while the other alphaviruses are transmitted by culicine mosquitoes. CHIKV has undergone adaptation to a new mosquito host which has increased its host range beyond Africa. Salmonid alphavirus is of economic importance in the farmed salmon and trout industry. It is postulated that future advances in research on alphavirus pathogenicity will come in the field of innate immunity. 1. Introduction Alphaviruses are small, enveloped, single-stranded positive RNA viruses of the family Togaviridae (Figure 1(a)). Most of them are mosquito transmitted and also infect a variety of mammals and birds. Their intracellular multiplication involves adsorption and receptor-mediated endocytosis into the cell cytoplasm. During intracellular multiplication a gene amplification mechanism results in the formation of a subgenomic RNA species that codes for the structural proteins only and is labelled 26S RNA (Figure 1(b)). The nonstructural and structural proteins are formed from different open reading frames by posttranslational cleavage pathways, and the assembled nucleocapsids bud from areas of the cell membrane or intracellular vesicles that have acquired envelope proteins, thus forming enveloped virions [1]. Figure 1: (a) The structure of alphavirus virions (e.g., SFV). (b) Alphavirus genome structure. P62 (also known as PE2) is the precursor to the E2 and E3 proteins. The genus Alphavirus contains approximately 30 members, which probably diverged a few thousand years ago. Eight alphaviruses, all of which can infect humans as well as other animals, will be discussed
%U http://www.hindawi.com/journals/isrn.virology/2013/861912/