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Study in the Year 2007: Taxonomy and Virology OF SARS-CoV

Group of Scientist already studied TAXONOMY AND VIROLOGY OF SARS-CoV in Year 2007 that SARS-CoV is one of 36 coronaviruses in the familyCoronaviridaewithin the orderNidovirales. Members of theCoronaviridaeare known to cause respiratory or intestinal in-fections in humans and other animals (Fig. 1). Despite amarked degree of phylogenetic divergence from other knowncoronaviruses, SARS-CoV together with bat SARS-CoV arenow considered group 2b coronaviruses (190, 282). Primaryisolation of SARS-CoV was achieved by inoculation of patients’ specimens into embryonal monkey kidney cell lines suchas FRhK-4 or Vero E6 cell lines, which produced cytopathicchanges at foci, where cells become round and refractile within5 to 14 days (259). These initial cytopathic changes spreadthroughout the cell monolayers, leading to cell detachmentwithin 24 to 48 h. Subcultures can be made on Vero (monkeykidney), Huh-7 (liver cancer) (301), CACO-2 (colonic carci-noma) (79) or other colorectal cancer, MvLu (mink lung epi-thelial) (104), and POEK and PS (pig) cell lines (122). Trans-mission electron microscopy of infected cell lines showedcharacteristic coronavirus particles within dilated cisternae ofrough endoplasmic reticulum and double-membrane vesicles.Clusters of extracellular viral particles adhering to the surfaceof the plasma membrane were also seen. Negatively stainedelectron microscopy showed viral particles of 80 to 140 nm withcharacteristic surface projections of surface proteins from thelipid envelope (89, 180, 259). SARS-CoV has a higher degree of stability in the environment than other known human coro-naviruses (91, 276). It can survive for at least 2 to 3 days on drysurfaces at room temperature and 2 to 4 days in stool (276).The electron microscopic appearance and genome order of5-replicase (Orf1ab)-structural proteins (spike [S]-envelope[E]-membrane [M]-nucleocapsid [N])-poly(T)-3are similar tothose of other members of theCoronaviridae(236). Similar toother coronaviruses, it is an enveloped positive-sense single-stranded RNA virus with a genome size of almost 30 kb (Fig.2). The genome is predicted to have 14 functional open readingframes (ORFs) (290). Their functions and putative roles areoutlined in Table 1. Two large 5-terminal ORFs, ORFs 1a and1b, encode 16 nonstructural proteins, 7 of which are likely to beinvolved in the transcription and replication of the largestgenome among all RNA viruses (92, 95, 158, 166, 242, 284, 309,316, 343, 414). The two proteases are involved in posttransla-tional proteolytic processing of the viral polyprotein (5, 15, 121, 224, 394). The surface S protein is involved in the attach-ment and entry of the host cell and is therefore the main targetfor neutralizing antibody and antiviral peptides (159, 206, 227,301, 334). N together with M, E, and Orf7a are involved in theassembly of the virion (97, 147, 150, 245, 359). Orf3a is an ionchannel protein that is likely to be involved in viral buddingand release (234). Analysis of genome sequences of many isolates of SARS-CoV from humans with civet SARS-CoV andbat SARS-CoV showed that the most variable genes with nu-cleotide homologies of less than 90% are the S gene,Orf3,Orf8,nsp2,nsp3, andnsp4(190, 215, 282). Deletions of 82 and415 nucleotides inOrf8were found in some human isolates,whereas a unique 29-nucleotide signature insertion inOrf8canbe found in animal isolates (64, 117). Therefore, the more conservedOrf1bis generally chosen to be the molecular targetfor the design of clinical diagnostic tests rather than these lessconserved regions.

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CLINICALMICROBIOLOGYREVIEWS, Oct. 2007, p. 660–694Vol. 20, No. 40893-8512/07/$08.000 doi:10.1128/CMR.00023-07Copyright © 2007, American Society for Microbiology. All Rights Reserved.Severe Acute Respiratory Syndrome Coronavirus as an Agent ofEmerging and Reemerging InfectionVincent C. C. Cheng, Susanna K. P. Lau, Patrick C. Y. Woo, and Kwok Yung Yuen*State Key Laboratory of Emerging Infectious Diseases, Department of Microbiology, Research Centre of Infection andImmunology, The University of Hong Kong, Hong Kong Special Administrative Region, China

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