SARS

The outbreak of SARS was first detected in 2003 in Hong Kong, Singapore, Toronto and Vietnam. The WHO described this disease as an atypical pneumonia (http://www.who.int/csr/sars/archive/2003_03_12/en/index.html).In the same year scientists identified the virus responsible for SARS (http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=12711465&dopt=AbstractPlus). The virus SARS-Co V was identified as the cause of this disease. In order to ensure patient management, tracing of contact and epidemiological study, a laboratory diagnosis to determine infection with the virus was required. Scientists succeeded in unraveling the complete genome code of the various strains of SARS – CoV. Serology examinations are required to confirm infection with this virus. These examinations help in determining the status of infection. Test for antibodies on viral lysate may give unreliable results as there exists a possibility that the virus lysate is produced due to the closely related other corona viruses that cause common cold. To overcome this problem, an isolation of whole virus dependent assays is required for the diagnosis of SARS – CoV infection. Further the Infected cell – dependent indirect immunofluorescence test for anti – SARS IgG antibody provides accurate results of infection with SARS – CoV. The immunofluorescence test is an excellent method for determining the reactivity of samples to screening assays (http://www.cdc.gov/ncidod/EID/vol10no3/03-0493.htm).

In addition, the procedure of Enzyme Immunoassay or EIA constitutes an efficient method for determining SARS – CoV antibodies. The results of this test are unambiguous to a significantly greater extent, in diagnosing viral infection, in comparison to the results obtained from RT-PCR. In the early stages of infection, the antibodies do not render themselves to detection and at that juncture, the sero conversion from negative to positive or an abnormal increase in antibody titer from acute to convalescent serum specimens, would be of immense help in detecting the presence of antibodies. If a serology test results proves to be positive, then it can be construed that the patient has been infected with the SARS – CoV. Furthermore, most patients of SARS develop antibodies within eight to ten days of being infected by the virus. However, some patients do not develop antibodies even after twenty – eight days from the onset of illness. For such patients the test has to be done on serum specimens collected after twenty eight days of the illness. The extant methods for serological diagnosis of SARS – CoV infection are antibody identification in acute and convalescent – phased serum samples of the patient by immunofluorescence assay and enzyme linked immunosorbent assay or ELISA with the extracts of cell culture (http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=12690092&ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVAbstractPlus ). The results of the examinations of indirect immunofluorescence assay and ELISA with tissue culture are not standard in comparison with ELISA based antibody detections examinations with recombinant antigens. In addition to this, the production of infected lines for coating the ELISA plates and the slides used therein require cultivation of SARS – CoV.

Some of the efficient techniques employed in serological testing are Enzyme Immunosorbent Assay or EIA and Immunofluorescence Assay or IFA. These techniques assist in determining the existence of anti – coronavirus antibodies. The possibility of a mixture of IgG and IgM antibodies being present in a SARS patient’s serum can be confirmed by using EIA techniques (http://www.cdc.gov/eid/content/13/10/pdfs/07-0576.pdf ). An uncomplicated, effective and non invasive test for detecting SARS was invented by microbiologists in Hong Kong (http://www.thd.org.tr/haber/goster.asp?HaberID=232). This test is a real time quantitative assay, which can be used usually within three to four hours of the commencement of the illness. In this test, the presence of coronavirus in the nasal swabs or throat cultures is tested in order to detect any antibody response in them (http://www.clinchem.org/cgi/data/49/4/DC1/1).

 

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