POST – Diagnostic Tests and the Immunology of Covid-19

As we all know, Covid-19 is a new virus for humans, and hence we know very little about this entity.

But, for a virus that has been a menace for only 4 months, we have learned an immense amount, through the aggressive research by the various academicians around the world.

Let’s try to understand some basic immunology of Covid-19.

*** This is VERY difficult to explain in “simple terms” ***

What is Covid-19?

  • Covid-19 = Corona Virus Disease identified in 2019
  • Covid-19 is an RNA virus (which is different from DNA, but a genetic material nonetheless)
  • Under magnification, the Covid-19 virus appears to have a “crown”
  • “Coronam” is the Latin term for “crown” ==> hence the name “Corona”

 

How long does the Covid-19 infection last?

  • If you have a “normal” immune system, your body will attack the virus and kill it over a period of 1-14 days
  • Your immune system and the immune response will determine the exact duration of infection
  • Since it can survive in your body for upto 14 days, you remain infectious for that duration
  • Hence, the rationale for a 14 day quarantine

 

How long can it survive OUTSIDE of your body?

  • It can survive on ANY surface for upto a “few days”
  • The exact duration is not 100% known
  • But, based on other viruses, it is assumed it can survive for a few hours on any surface
  • If Covid-19 behaves like other such viruses, heat and humidity will kill the virus much more rapidly
    • Hence, the whisper that the virus will “die off” once summer arrives

 


Currently Available Test – Covid-19 Genetic Test

  • The “genetic code” for this virus was identified and sequenced fairly quickly by a Chinese scientist
  • Once the “genetic code” was sequenced, scientists very quickly developed a diagnostic test to identify segments of this genetic code
  • This is the test that is currently being used in the US
  • As long as you have the virus in your throat or upper respiratory tract, a cotton swab of your throat can be tested for the genetic code
  • But, as soon as your infection is cleared, and the virus is no longer found in your throat, the genetic test will turn “normal”
  • Hence, as of March 23, 2020, the genetic test will ONLY tell us if you have a CURRENT, ACTIVE INFECTION
  • It does NOT tell us if you previously had an infection

Covid-19 Immunology

  • The way our body fights any infection is through the “immune system”.
  • One of the components of the immune system is called an “antibody” (abbreviated “Ab”)
  • There are various “types” of antibodies
    • 2 important antibody types for fighting such infections are IgM and IgG
  • Normally, a new infection will trigger the natural creation of IgM Ab
  • After a certain amount of time, IgG Ab are created
  • Depending on the type of infection, the time it takes to develop IgM or IgG Ab will vary.
    • IgM Ab will typically disappear after the infection is treated
    • IgG Ab will linger for many months to years after the infection is cleared
  • Since the Covid-19 science is still emerging, we do NOT know how long it takes for any individual to develop IgM or IgG Ab
  • Typically, we CANNOT get re-infected with the same virus AFTER our body has created IgG
    • IgG will fight off any re-infection by the same virus
    • So, theoretically, we should only get this infection once

New Tests on the Horizon – Covid-19 Antibody Tests

  • As recent as earlier today (March 23, 2020), various Pharma companies have submitted requests to approve a new ANTIBODY test
  • These new tests do NOT test for the genetic material
  • Rather, they test for the Ab
  • Some of the new tests will detect IgM, while others will detect IgG

Summary of Immunology

  • After an infection, your body creates IgM and IgG Ab
    • IgM Ab can be detected EARLY in an infection
    • IgG can be detected LATE in the infection cycle
  • If you are able to detect IgM Ab with lab testing, that will indicate a new or recent infection
  • If you are able to detect IgG Ab with lab testing, that will indicate an OLD infection
    • But, IgG does not tell you WHEN the infection occurred — whether the infection occurred a few months ago or a few years ago

How will these different tests (Genetic and Antibody) be used?

  • Over the next few weeks, we will probably see a multi-prong testing approach
  • We will probably use the genetic test to look for ACTIVE infection
  • We will also use the IgG Ab test to see if an individual HAS PREVIOUSLY had the infection
    • This is important, because if we develop IgG Ab from a previous infection, our immune system can now fight off any new infection, and most likely, we will not get the infection again
  • Hopefully, if you have IgG Ab, you can resume your normal life, without fear of getting the infection again

How does a vaccine work?

  • When we are given a vaccine, we are given part of the viral genetic code
  • This partial genetic code allows our body to self-create IgM and IgG Ab, without getting the actual infection
  • A successful vaccine induces our bodies to create IgG Ab, which is used to fight off any new infection

 

Stay Safe !

  • Sudhir S. Athni, MD

 

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