The COVID-19 pandemic, caused by the SARS-CoV-2 virus, has led to more than two hundred million confirmed cases, with over 4 million deaths globally, as of September 07, 2021.
The living and working conditions of billions of people worldwide have been significantly disrupted due to different forms of social distancing and lockdowns in many cities.
The world economy has been remarkably weakened as a result of business shutdowns and major restrictions on travel.
Widespread availability of accurate and rapid testing procedures is extremely valuable in unraveling the complex dynamics involved in SARS-CoV-2 infection and immunity.
To this end, laboratories, Research centers, and companies around the world have been racing to develop and produce critically needed test kits.
The Diagnostic Testing Methods.
Reverse Transcription-Polymerase Chain Reaction (Rt-Pcr)
PCR tests are used to directly screen for the presence of viral RNA, which will be detectable in the body before antibodies form or symptoms of the disease are present.
This means the tests can tell whether or not someone has the virus very early on in their illness.
During Covid-19 PCR testing, substances known as reverse transcriptase or DNA polymerase are added to a nasopharyngeal sample in a lab.
These substances work to make numerous copies of any viral RNA that may be present. This is so that enough copies of the RNA are present to signal a positive result, as specifically designed primers and probes attach themselves to sequences of the genetic code of the virus to signal that a pathogen has been found.
Because COVID-19 exhibits a range of clinical manifestations, from mild flu-like symptoms to life-threatening conditions, it is important to have efficient testing during the early stages of infection to identify COVID-19 patients from those with other illnesses.
Early diagnosis permits physicians to provide prompt intervention for patients who are at higher risk for developing more serious complications from COVID-19 illness.
More complicated diagnostic testing based on viral genomic sequencing is an essential tool for determining the rate and degree of mutational variability associated with SARS-CoV-2 and for identifying newly emerging strains of the virus for more effective vaccine development.
Covid-19 Tests Currently Fall Into Two Major Categories.
The first category includes molecular assays for detection of SARS-CoV-2 viral RNA using polymerase chain reaction (PCR)-based techniques or nucleic acid hybridization-related strategies.
The second category includes serological and immunological assays that largely rely on detecting antibodies produced by individuals as a result of exposure to the virus or on detection of antigenic proteins in infected individuals.
It is important to reemphasize that these two categories of tests serve overlapping purposes in management of the COVID-19 pandemic. Testing for SARS-CoV-2 viral RNA identifies SARS-CoV-2-infected individuals during the acute phase of infection.
Serological testing subsequently identifies individuals who have developed antibodies to the virus and could be potential convalescent plasma donors
Serological And Immunological Assays
While RT-PCR-based viral RNA detection has been widely used in diagnosis of COVID-19, it cannot be used to monitor the progress of the disease stages and cannot be applied to broad identification of past infection and immunity.
Serological testing is defined as an analysis of blood serum or plasma and has been operationally expanded to include testing of saliva, sputum, and other biological fluids for the presence of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies
IgM first becomes detectable in serum after a few days and lasts a couple of weeks upon infection and is followed by a switch to IgG. Thus, IgM can be an indicator of early stage infection, and IgG can be an indicator of current or prior infection.
The determination of SARS-CoV-2 exposure relies largely on the detection of either IgM or IgG antibodies that are specific for various viral antigens including, but not exclusively, the spike glycoprotein (S1 and S2 subunits, receptor-binding domain) and nucleocapsid protein.
The methodology for these determinations includes the traditional enzyme-linked immunosorbent assay (ELISA), immunochromatographic lateral flow assay, neutralization bioassay, and specific chemosensors. Each of these formats brings advantages (speed, multiplexing, automation) and disadvantages (trained personnel, dedicated laboratories).
Most people who catch and recover from COVID-19 are likely to be immune for several months afterwards, a study of more than 20,000 health-care workers in the United Kingdom has found.
The study — called SARS-CoV-2 Immunity and Reinfection Evaluation (SIREN) -concluded that immune responses from past infection reduce the risk of catching the virus again by 83% for at least 5 months.
As Pathcare ,we should take a bold step towards the new world of covid-19 diagnosis in the following areas.
viral genomic sequencing is an essential tool for determining the rate and degree of mutational variability associated with SARS-CoV-2.
Sars-Cov 2 Serological Studies For Antibodies.