Article Writer-   Om Bikash Sahu, Int. MSc., School of Biological Sciences, NISER, Odisha(India)

Coronavirus disease 2019 (COVID-19) which we all know is an infectious disease is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus emerged in the human population in the final months of 2019 and is now continuously growing in the globe in an exponential manner. The (SARS-CoV-2) pandemic poses an enormous burden on society, economics, and healthcare systems worldwide.

Till now there are no vaccines or drugs available in the world to diagnose the viral infection. so, the only thing that can be done is to slow the spread by isolating the COVID-19 positive person so that it will be beneficial to all. So, a greater number of tests are required for this.

The concept behind the test:

The different country uses different types of tests to identify COVID-19 positive. Can you guess the concept behind this? Let’s discuss this.

How we can able to know if one is affected by the virus or not. The basic concept is the presence of the virus in the infected area. if the virus is present in the infected area then we can able to find out the person is positive otherwise he is negative for the test. It is the direct method of identification. We know we have the defense system in our body which produces the antibodies to fight for us against the enemy(antigen) which can be viruses,bacteria, etc. So here comes the second concept of the test which says if we generate the antibody in our body against the virus the test detects this. So that it is an indirect method of testing of COVID-19.

Broadly, there are two kinds of tests that are available for COVID-19

1.Molecular (Viral) test -It is based on the first concept. (RT-PCR) which gives information about the active infection i.e. presence of viral infection at the time of the test, which is the direct method of testing. In this type of test at first nasal/throat swab from the person is taken and RNA extraction occurs which is the genetic material of the virus. By doing RT-PCR technology from the RNA, cDNA can be synthesized by using reverse transcriptase enzyme and dNTPs. The sample contains a very low amount of genetic material so we have to amplify it. if it has the same genetic sequence that of the SARS-CoV-2 virus it shows positive. For identification of the genetic material of the virus, fluorophore molecules are used. If the graph on the computer detects these fluorophore molecules and shows a hike. If not them the sample doesn’t have the sequence of virus RNA and the result is negative.

2.Antibody test -this type of test gives information about the previous infections. This is also known as a serological test. As it is based on the second type of concept so this type of test detects the presence of antibody (which is specific to antigen) in our body which is generally created by the attack of any foreign antigen which may be virus or bacteria. This test cannot identify the presence of the virus in the body so it is indirect of testing. This is generally used for the elimination of the faulty tests.

The technician will take 1drop of blood by finger prick. Then put the blood in the antibody testing kit (identical to malaria and pregnancy test kit) for COVID-19 and apply buffer which comes with the test kit which helps the blood to diffuse.

There are 4 sites in the test kit.

 1. S region – it is the sample region where a blood sample is applied. Then the buffer is also applied here for the running of the blood.
2. c region – control region – if the test kit is showing a line in control then the test kit is correct and usable if not then it is faulty.
3. For IgM – it is the antibody region. It is the primary antibody which shows that there is the production of the antibody for the 1st time.
4. For IgG – it is the antibody region. It is the secondary antibody. Which shows that there is the production of the antibody multiple time.

If a person gets a single line in the c region then he never infected by the virus. If a person gets lines in the c-region and the IgM region then in 1-3 weeks before the test he was infected by the virus. And if a person gets a line in all 3 regions i.e. c-region, IgM, and IgG region then he was infected by it multiple times.

Conclusion–

Both techniques have their own benefits. RT-PCR is good at finding the present infections whereas the antibody test is good to find whether a person is infected by it or not. RT-PCR is time taking, costly and also require expertise hand whereas the antibody can be done by the person himself and also result comes within 15 mins. In this way, the tests are performed to identify whether a person is positive or negative to the COVID-19.

References:

1.Subbaraman N. Coronavirus tests: researchers chase new diagnostics to fight the pandemic [published online ahead of print, 2020 Mar 23]. Nature. 2020;10.1038/d41586-020-00827-6. doi:10.1038/d41586-020-00827-6
2.Min‐Kyu Oh, Yasuyuki Sakai, Yu‐Chen Hu, Asian Congress on Biotechnology 2019, Biotechnology Journal, 10.1002/biot.202000214, 15, 6, (2020).
3.”Advice on the use of point-of-care immunodiagnostic tests for COVID-19″, url- https://www.who.int/news-room/commentaries/detail/advice-on-the-use-of-point-of-care-immunodiagnostic-tests-for-covid-19
4.Jacofsky D, Jacofsky EM, Jacofsky M. Understanding Antibody Testing for COVID-19. J Arthroplasty. 2020 Jul;35(7S):S74-S81. doi: 10.1016/j.arth.2020.04.055. Epub 2020 Apr 27. PMID: 32389405; PMCID: PMC7184973.
5.https://pubs.rsna.org/doi/10.1148/radiol.2020200642
6.https://www.fda.gov/media/135763/download