Comparison of 9 different PCR primers for the rapid detection of severe acute respiratory syndrome coronavirus using 2 RNA extraction methods

The sensitivity and specificity of various severe acute respiratory syndrome coronavirus (SARS-CoV) PCR primer and probe sets were evaluated through the use of commercial kits and in-house amplification formats. Conventional and real-time PCR assays were performed using a heat-block thermocycler ABI 9600, the Roche LightCycler™ version 1.2, or the ABI 7000 Sequence Detection System. The sensitivity of all primers was between 0.0004 and 0.04 PFU with viral cell lysate and between 0.004 and 0.4 PFU in spiked stool specimen per PCR assay. The primer sets for real-time PCR assays were at one least 1 log more sensitive than the primer sets used in the conventional PCR. A panel of viruses including swine gastroenteritis virus, bovine coronavirus, avian bronchitis virus (Connecticut strain), avian bronchitis virus (Massachusetts strain), human coronaviruses 229E and OC43, parainfluenza virus (type III), human metapneumovirus, adenovirus, respiratory syncytial virus, and influenza A were tested by all assays. All real-time PCR assays used probe-based detection, and no cross-reactivity was observed. With conventional PCR, analysis was performed using agarose gel electrophoresis and multiple nonspecific bands were observed. Two commercial extraction methods, magnetic particle capture and silica-based procedure were evaluated and the results were comparable. The former was less laborious with shorter time for completion and can easily be adapted to an automated system such as the MagNa Pure-LC, which can extract nucleic acid from clinical samples and load it into the sample capillaries of the LightCycler™. As exemplified by this study, the continued refinement and evaluation of PCR procedures will greatly benefit the diagnostic laboratory during an outbreak of SARS.

Colonization of severe acute respiratory syndrome-associated coronavirus among health-care workers screened by nasopharyngeal swab

STUDY OBJECTIVES

To report the efficacy and findings of a large-scale preventive screening program for severe acute respiratory syndrome-associated coronavirus (SARS-CoV) using amplification of the virus from a nasopharyngeal swab (NPS) obtained from the health-care workers (HCWs).

DESIGN

A prospective observational study.

SETTING

A medical center in Taiwan.

PARTICIPANTS

Two hundred thirty HCWs.

INTERVENTION

NPS examination for the presence of SARS-CoV by two nested reverse transcription-polymerase chain reaction (RT-PCR) assays.

MEASUREMENTS AND RESULTS

During the outbreak of severe acute respiratory syndrome (SARS), NPS polymerase chain reaction screening of HCWs for SARS-CoV was performed. SARS-CoV was examined by two nested RT-PCRs and a quantitative RT-PCR. Serum-specific antibodies were assessed by enzyme immunoassay and indirect immunofluorescence. We monitored 230 HCWs, including 217 first-line HCWs and 13 non-first-line HCWs. One hundred ninety first-line HCWs and 13 non-first-line HCWs had negative results in both nested RT-PCR assays. Two first-line HCWs who were positive on both nested RT-PCR assays had SARS. They had 16,900 +/- 7,920 copies (mean +/- SD) of RNA per milliliter in the NPS and had detectable anti-SARS antibodies. The remaining 25 first-line HCWs were negative for the first nested RT-PCR but positive for the second nested RT-PCR. Their corresponding titers were 338 +/- 227 copies of RNA per milliliter; antibodies developed in none of these 25 HCWs. The expression and function of angiotensin-converting enzyme-2 were not different among these HCWs. This study shows that colonization of SARS-CoV occurred in 25 of 217 well-protected first-line HCWs on a SARS-associated service, but they remained seronegative.

CONCLUSION

With the second RT-PCR assay more sensitive than the first RT-PCR assay, we are able to show that approximately 11.5% of well-protected HCWs exposed to SARS patients or specimens may have colonization without seroconversion. Only those with significant clinical symptoms or disease would have active immunity. Thus, regular NPS screening for nested RT-PCR assays in conjunction with a daily recording of body temperature in all first-line HCWs may provide an effective way of early detection.

China: open season

SARS caught China unawares. But the ensuing struggle to characterize and contain the virus has put the country's work on infectious diseases back on target. Apoorva Mandavilli reports.

China's recent SARS outbreak put the spotlight on the nation's scientists. Many labs cast their usual work aside to tackle SARS biochemistry, epidemiology and immunology. Chinese scientists continue to publish important work in the field, which is good news for the global response to any infectious diseases newly emerging from Asia. But will the government foster the openness that such responses need?

Automated extraction protocol for quantification of SARS-coronavirus RNA in serum: an evaluation study

BACKGROUND

We have previously developed a test for the diagnosis and prognostic assessment of the severe acute respiratory syndrome (SARS) based on the detection of the SARS-coronavirus RNA in serum by real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR). In this study, we evaluated the feasibility of automating the serum RNA extraction procedure in order to increase the throughput of the assay.

METHODS

An automated nucleic acid extraction platform using the MagNA Pure LC instrument (Roche Diagnostics) was evaluated. We developed a modified protocol in compliance with the recommended biosafety guidelines from the World Health Organization based on the use of the MagNA Pure total nucleic acid large volume isolation kit for the extraction of SARS-coronavirus RNA. The modified protocol was compared with a column-based extraction kit (QIAamp viral RNA mini kit, Qiagen) for quantitative performance, analytical sensitivity and precision.

RESULTS

The newly developed automated protocol was shown to be free from carry-over contamination and have comparable performance with other standard protocols and kits designed for the MagNA Pure LC instrument. However, the automated method was found to be less sensitive, less precise and led to consistently lower serum SARS-coronavirus concentrations when compared with the column-based extraction method.

CONCLUSION

As the diagnostic efficiency and prognostic value of the serum SARS-CoV RNA RT-PCR test is critically associated with the analytical sensitivity and quantitative performance contributed both by the RNA extraction and RT-PCR components of the test, we recommend the use of the column-based manual RNA extraction method.

Seroprevalence of SARS coronavirus antibody in household contacts

Between March and July 2003, 671 cases of severe acute respiratory syndrome (SARS) were diagnosed in Taiwan with a total of 84 fatalities. After the epidemic, a serological survey was conducted involving the asymptomatic household contacts. Household contacts of 13 index patients were enrolled in the study. Contact history and clinical symptoms of the household contacts were recorded by standardized questionnaires. Blood samples of patients and household contacts were collected at least 28 days after symptom onset in the index patients or household exposure in the contacts for SARS-associated coronavirus (SARS-CoV) IgG testing. On the basis of this investigation, 29 persons (25 adults and 4 children) were identified as having had unprotected exposure to the index cases before infection-control practices were implemented. Laboratory evaluation of clinical specimens showed no evidence of transmission of SARS-CoV infection to any contacts. This investigation demonstrated that subclinical transmission among household contacts was low in the described setting.

[Some medical staff positive for serum SARS coronavirus antibody IgG have only mild symptoms]

OBJECTIVE

To identify patients with SARS coronavirus infection who have only mild symptoms.

METHOD

Enzyme-linked immunosorbent assay was employed to detect serum antibody against SARS coronavirus in the lysate of whole SARS coronavirus from 19 SARS patients and 200 medical staff members without obvious SARS symptoms after possible exposure to the virus during routine medical practice.

RESULTS

Serum IgG antibody against SARS coronavirus was detected in all the 19 SARS patients, and among the 200 staff members, 20 (10%) were found positive for the antibody but with no obvious or only mild symptoms.

CONCLUSION

Serum IgG antibody against SARS coronavirus is positive in a small proportion (around 10%) of the medical staff members exposed to the virus in our hospital, but may not cause obvious symptoms, suggesting SARS coronavirus infection might in some cases have mild or even no clinical manifestations.

Real-time NASBA detection of SARS-associated coronavirus and comparison with real-time reverse transcription-PCR

Severe acute respiratory syndrome (SARS) exhibits a high mortality rate and the potential for rapid epidemic spread. Additionally, it has a poorly defined clinical presentation, and no known treatment or prevention methods. Collectively, these factors underscore the need for early diagnosis. Molecular tests have been developed to detect SARS coronavirus (SARS-CoV) RNA using real time reverse transcription polymerase chain reaction (RT-PCR) with varying levels of sensitivity. However, RNA amplification methods have been demonstrated to be more sensitive for the detection of some RNA viruses. We therefore developed a real-time nucleic acid sequence-based amplification (NASBA) test for SARS-CoV. A number of primer/beacon sets were designed to target different regions of the SARS-CoV genome, and were tested for sensitivity and specificity. The performance of the assays was compared with RT-PCR assays. A multi-target real-time NASBA application was developed for detection of SARS-CoV polymerase (Pol) and nucleocapsid (N) genes. The N targets were found to be consistently more sensitive than the Pol targets, and the real-time NASBA assay demonstrates equivalent sensitivity when compared to testing by real-time RT-PCR. A multi-target real-time NASBA assay has been successfully developed for the sensitive detection of SARS-CoV.

The severe acute respiratory syndrome (SARS)

The world was shocked in early 2003 when a pandemic of severe acute respiratory syndrome (SARS) was imminent. The outbreak of this novel disease, caused by a novel coronavirus (the SARS-coronavirus), hit hardest in the Asian Pacific region, though eventually it spread to five continents. The speed of the spread of the SARS epidemic was unprecedented due to the highly efficient intercontinental transportation. An international collaborative effort through the World Health Organization (WHO) has helped to identify the aetiological agent about 1 month after the onset of the epidemic. The power of molecular biology and bioinformatics has enabled the complete decoding of the viral genome within weeks. Over 1000 publications on the phylogeny, epidemiology, genomics, laboratory diagnostics, antiviral, immunization, pathogenesis, clinical disease, and management accumulated within just 1 year. Although the exact animal reservoir of virus and how it evolved into a human pathogen are still obscure, accurate diagnosis and epidemiological control of the disease are now possible. This article reviews what is currently known about the virus and the disease.

Double-antigen sandwich ELISA for detection of antibodies to SARS-associated coronavirus in human serum

The study presented here was conducted to evaluate the performance of a double-antigen sandwich ELISA to detect antibodies in human serum against the coronavirus associated with severe acute respiratory syndrome (SARS). A recombinant partial nucleocapsid protein of SARS-associated coronavirus was used as a serodiagnostic antigen in the ELISA. A total of 2892 clinical serum samples were tested with the ELISA kit, which positively identified 25 of 35 (71.4%) samples of patients with confirmed SARS infection, 286 of 407 (70%) samples of patients suspected of having SARS, 229 of 302 (75.8%) samples of convalescent SARS patients, and 0 of 544 samples obtained from healthcare workers; only 1 of 1604 clinical samples obtained from patients with other diseases demonstrated a weakly positive result. These results indicate that the double-antigen sandwich ELISA is an effective screening method for the serodiagnosis of SARS-associated coronavirus.

Scalable transcriptional analysis routine--multiplexed quantitative real-time polymerase chain reaction platform for gene expression analysis and molecular diagnostics

We report the development of a new technology for simultaneous quantitative detection of multiple targets in a single sample. Scalable transcriptional analysis routine (STAR) represents a novel integration of reverse transcriptase-polymerase chain reaction and capillary electrophoresis that allows detection of dozens of gene transcripts in a multiplexed format using amplicon size as an identifier for each target. STAR demonstrated similar or better sensitivity and precision compared to two commonly used methods, SYBR Green-based and TaqMan probe-based real-time reverse transcriptase-polymerase chain reaction. STAR can be used as a flexible platform for building a variety of applications to monitor gene expression, from single gene assays to assays analyzing the expression level of multiple genes. Using severe acute respiratory syndrome (SARS) corona virus as a model system, STAR technology detected single copies of the viral genome in a two-gene multiplex. Blinded studies using RNA extracted from various tissues of a SARS-infected individual showed that STAR correctly identified all samples containing SARS virus and yielded negative results for non-SARS control samples. Using alternate priming strategies, STAR technology can be adapted to transcriptional profiling studies without requiring a priori sequence information. Thus, STAR technology offers a flexible platform for development of highly multiplexed assays in gene expression analysis and molecular diagnostics.

Preparation and development of equine hyperimmune globulin F(ab')2 against severe acute respiratory syndrome coronavirus

AIM

The resurgence of severe acute respiratory syndrome (SARS) is still a threat because the causative agent remaining in animal reservoirs is not fully understood, and sporadic cases continue to be reported. Developing high titers of anti-SARS hyperimmune globulin to provide an alternative pathway for emergent future prevention and treatment of SARS.

METHODS

SARS coronavirus (CoV)F69 (AY313906) and Z2-Y3 (AY394989) were isolated and identified from 2 different Cantonese onset SARS patients. Immunogen was prepared from SARS-CoV F69 strain. Six health horses were immunized 4 times and serum was collected periodically to measure the profile of specific IgG and neutralizing antibodies using indirect enzyme-linked immunosorbent assay and a microneutralization test. Sera were collected in large amounts at the peak, where IgG was precipitated using ammonium sulphate and subsequently digested with pepsin. The product was then purified using anion-exchange chromatography to obtain F(ab')2 fragments.

RESULTS

The specific IgG and neutralizing antibody titers peaked at approximately week 7 after the first immunization, with a maximum value of 1:14210. The sera collected at the peak were then purified. Fragment of approximately 15 g F(ab')2 was obtained from 1litre antiserum and the purity was above 90% with the titer of 1:5120, which could neutralize the other strain (SARS-CoV Z2-Y3) as well.

CONCLUSION

This research provides a viable strategy for the prevention and treatment of SARS coronavirus infection with equine hyperimmune globulin, with the purpose of combating any resurgence of SARS.

Recurrent mutations associated with isolation and passage of SARS coronavirus in cells from non-human primates

Four clinical isolates of SARS coronavirus were serially passaged in two primate cell lines (FRhK4 and Vero E6). Viral genetic sequences encoding for structural proteins and open reading frames 6–8 were determined in the original clinical specimen, the initial virus isolate (passage 0) and at passages 5, 10, and 15. After 15 passages, a total of 15 different mutations were identified and 12 of them were non‐synonymous mutations. Seven of these mutations were recurrent mutation and all located at the spike, membrane, and Orf 8a protein encoding sequences. Mutations in the membrane protein and a deletion in ORF 6–8 were already observed in passage 0, suggesting these amino acid substitutions are important in the adaptation of the virus isolate in primate cell culture. A mutation in the spike gene (residue 24079) appeared to be unique to adaptation in FRhK4 cells. It is important to be aware of cell culture associated mutations when interpreting data on molecular evolution of SARS coronavirus. J. Med. Virol. 76:435–440, 2005. © 2005 Wiley‐Liss, Inc.

Molecular diagnosis of severe acute respiratory syndrome: the state of the art

Severe acute respiratory syndrome (SARS) first appeared in Guangdong Province, China, in November 2002. Although virus isolation and serology were useful early in the SARS outbreak for diagnosing new cases, these tests are not generally useful because virus culture requires a BSL-3 laboratory and seroconversion is often delayed until 2 to 3 weeks after infection. The first qualitative reverse transcriptase-polymerase chain reaction tests for SARS-coronavirus (CoV) were sensitive and capable of detecting 1 to 10 genome equivalents. These assays were quickly supplemented with quantitative real-time assays that helped elucidate the natural history of SARS, particularly the initial presence of low viral loads in the upper respiratory tract and high viral loads in the lower respiratory tract. The unique natural history of SARS-CoV infection dictates the testing of both respiratory and nonrespiratory specimens, the testing of multiple specimens from the same patient, and sending out positives to be confirmed by a reference laboratory. Commercially available reverse transcriptase-polymerase chain reaction tests for SARS have recently appeared; however, meaningful evaluations of these assays have not yet been performed and their true performance has not been determined. These and other issues related to diagnosis of SARS-CoV infection are discussed in this review.

History and recent advances in coronavirus discovery

Human coronaviruses, first characterized in the 1960s, are responsible for a substantial proportion of upper respiratory tract infections in children. Since 2003, at least 5 new human coronaviruses have been identified, including the severe acute respiratory syndrome coronavirus, which caused significant morbidity and mortality. NL63, representing a group of newly identified group I coronaviruses that includes NL and the New Haven coronavirus, has been identified worldwide. These viruses are associated with both upper and lower respiratory tract disease and are likely common human pathogens. The global distribution of a newly identified group II coronavirus, HKU1, has not yet been established. Coronavirology has advanced significantly in the past few years. The SARS epidemic put the animal coronaviruses in the spotlight. The background and history relative to this important and expanding research area are reviewed here.

Orchitis: a complication of severe acute respiratory syndrome (SARS)

Severe acute respiratory syndrome (SARS) coronavirus has been known to damage multiple organs; however, little is known about its impact on the reproductive system. In the present study, we analyzed the pathological changes of testes from six patients who died of SARS. Results suggested that SARS caused orchitis. All SARS testes displayed widespread germ cell destruction, few or no spermatozoon in the seminiferous tubule, thickened basement membrane, and leukocyte infiltration. The numbers of CD3+ T lymphocytes and CD68+ macrophages increased significantly in the interstitial tissue compared with the control group (P < 0.05). SARS viral genomic sequences were not detected in the testes by in situ hybridization. Immunohistochemistry demonstrated abundant IgG precipitation in the seminiferous epithelium of SARS testes, indicating possible immune response as the cause for the damage. Our findings indicated that orchitis is a complication of SARS. It further suggests that the reproductive functions should be followed and evaluated in recovered male SARS patients.

Rapid and sensitive detection of multiple genes from the SARS-coronavirus using quantitative RT-PCR with dual systems

The outbreak of severe acute respiratory syndrome (SARS) was caused by a newly identified coronavirus (SARS‐CoV) in 2003. To detect early SARS‐CoV infection, a one‐step, real‐time quantitative reverse transcription‐polymerase chain reaction (RT‐PCR) assay was developed that could simultaneously detect nucleocapsid (N), membrane (M), and spike (S) genes of SARS‐CoV with the same PCR condition using either Applied Biosystems (ABI) Prism 7700 Sequence Detection System or Roche LightCycler. The sensitivity of this assay was evaluated using cell culture‐derived viruses, in vitro transcribed viral RNA, and clinical specimens. The SARS‐S, ‐M, and ‐N primer/probe sets described in this paper could detect one to ten copies of in vitro transcribed S, M, and N RNA per test using both the ABI and Roche assay systems. The relative sensitivities for detecting cell culture‐derived SARS‐CoV were 0.01, 0.01, and 0.001 PFU/test, respectively. It showed that SARS‐N has comparable detection efficiencies to SARS2 and SARS3 which are primers sets designed by Centers for Disease Control and Prevention. In addition, SARS‐S and SARS‐M also demonstrated equivalent sensitivity to the commercially available RealArt HPA‐Coronavirus reagents (Artus). The relative sensitivity of these primer/probe sets was also examined using human sera spiked viruses and clinical specimens from four confirmed SARS patients. Similar results as above were obtained. Specificity tests and sequence alignment showed that these primer/probe sets annealed perfectly to 31 isolates of SARS‐CoV; and there was no cross detection with other coronaviruses and human respiratory tract‐associated viruses. Therefore, not only is it compatible with the ABI and Roche systems, this multiple‐gene detection assay also has the merit of being a rapid, safe, sensitive, and specific tool for accurate diagnosis of SARS‐CoV infection. J. Med. Virol. 77:151–158, 2005. © 2005 Wiley‐Liss, Inc.

[Expression of SARS-CoV in various types of cells in lung tissues]

OBJECTIVE

To investigate the cell types infected by severe acute respiratory syndrome-associated coronavirus (SARS-CoV) in lung tissues and explore the mechanism of lung injury in SARS.

METHODS

In-situ hybridization(ISH) and immunohistochemistry(IHC) double staining was applied to study the lung tissues from 7 SARS cases of Beijing and one of Anhui province. According to SARS-CoV genome sequence, the cDNA probe was synthesized and labelled by digoxin. Immunohistochemically, antibodies of cytokeratin(CK), CD34, CD68, Vimentin and CD3 were applied to demonstrate bronchial epithelial cells, type II pneumocytes, endothelial cells, macrophages, fibroblasts and T cells respectively.

RESULTS

The positive results of in-situ hybridization showed that the lung tissues of all cases expressed SARS-CoV RNA, and positive signals displayed in cytoplasms (purple-blue, NBP-BCIP. ISH-IHC double staining showed that positive signals of both ISH (purple-blue NBT-BCIP and IHC (red-brown, AEC expressed in the cytoplasms (purple and red). The positive results of double staining indicated that bronchial epithelial cells, type II pneumocytes, endothelial cells, macrophages, fibroblasts and T lymphocytes were diffusely infected by SARS-CoV.

CONCLUSION

This study of ISH-IHC double staining in lung tissues of SARS patients showed that bronchial epithelial cells, type II pneumocytes, endothelial cells, macrophages, T lymphocytes and fibroblasts were attacked diffusely in SARS lungs. Various types of cells damaged by SARS-CoV and inflammatory mediators released by those cells play an important role in the pathogenesis of lung injury in SARS.

SARS CTL vaccine candidates; HLA supertype-, genome-wide scanning and biochemical validation

Abstract:  An effective Severe Acute Respiratory Syndrome (SARS) vaccine is likely to include components that can induce specific cytotoxic T‐lymphocyte (CTL) responses. The specificities of such responses are governed by human leukocyte antigen (HLA)‐restricted presentation of SARS‐derived peptide epitopes. Exact knowledge of how the immune system handles protein antigens would allow for the identification of such linear sequences directly from genomic/proteomic sequence information (Lauemoller et al., Rev Immunogenet 2001: 2: 477–91). The latter was recently established when a causative coronavirus (SARS‐CoV) was isolated and full‐length sequenced (Marra et al., Science 2003: 300: 1399–404). Here, we have combined advanced bioinformatics and high‐throughput immunology to perform an HLA supertype‐, genome‐wide scan for SARS‐specific CTL epitopes. The scan includes all nine human HLA supertypes in total covering >99% of all individuals of all major human populations (Sette & Sidney, Immunogenetics 1999: 50: 201–12). For each HLA supertype, we have selected the 15 top candidates for test in biochemical binding assays. At this time (approximately 6 months after the genome was established), we have tested the majority of the HLA supertypes and identified almost 100 potential vaccine candidates. These should be further validated in SARS survivors and used for vaccine formulation. We suggest that immunobioinformatics may become a fast and valuable tool in rational vaccine design.