By Mrinalini Watsa
Disease testing sounds complicated. Reading about it in the news in the context of the ongoing COVID-19 pandemic is even worse. If you are pretty sure that you’ve read contradictory news articles — you are not wrong!
Most of them don’t slow down to explain that there are actually multiple ‘coronavirus tests’ , which are usually conflated willy-nilly , producing justifiable confusion in a reader.
The goal of this article is simple: clarity. And I will continually work on it until this goal is achieved, so feel free to point out inconsistencies or obscured meanings — never, ever be afraid to admit that you cannot understand this biology. After all, understanding it could be the difference between endless quarantine and a return to normalcy, a diagnosis of COVID-19 or a mild cold.
It’s critical to understand. Thankfully, it’s also relatively simple.
. . .
A Little Biology:
- SARS-CoV-2 is the virus causing the disease we call COVID-19. If you want to call it ‘coronavirus’ you can, but it would be like me calling you a primate, instead of at least identifying you by your species — a human. There are many strains or species of coronaviruses, and SARS-CoV-2 is the one we are fighting today.
- The coronaviruses are like us in that they have a genome. This means, they have genetic material, or a set of molecules that serve as instructions for our cells to produce the proteins that our bodies need to survive. Every genome contains genes interspaced with other genetic material. Most cells in your body have an entire genome in them.
- Viruses are NOT like us in that they do not have cells. A virus is just a shell of proteins with genetic material inside it. People are still arguing about whether we can even deem them to be alive. Creepy, I know.
- Viral genomes can contain DNA or RNA: the only difference between them is a single letter in the code. DNA’s code is made up of four molecules we call A, T, C, and G. In RNA, the T is replaced with a U molecule. Further, viral genomes can be double or single stranded and each kind behaves differently inside a host cell to multiply itself.
- Viruses are incredibly simple organisms that don’t have a lot of machinery to for self-replication, so they typically hijack a host’s cell’s machinery to make more copies of themselves. First, viruses bind to a host cell through specific receptors on its surface. They then either merge their membranes with the host cell, depositing their contents into the cell, or are eaten by a host cell in a process called endocytosis. Once inside, they strip their protein coats off, and release their genetic material, which form messenger RNA or mRNA. Diabolically, these mRNA are then converted by the host’s own ribosomes (organelles in the cells) into viral proteins!
The illustration below shows how the virus is pulled into a host’s cell, shooting out its messenger RNA (the orange strands) which eventually are the basis for the creation of more viral proteins that are used to construct new viruses.
Test 2: The Test for Immunity
This test is based on an ELISA — or an Enzyme-Linked ImmunoSorbent Assay. It is designed to target a specific antibody, which is a type of molecule (a protein) that your blood releases in response to an antigen (also a protein) produced by a foreign object, like the virus, in your body.
There are a few different types of ELISAs out there, and here is a brilliant video on how they function. But, there is one important caveat. In the test video below, the antigen = the antibody your body has made in response to the virus. ‘Antigen’ is used here as a generic term for the thing you are trying to detect (the blue, funny shaped molecule). Just remember that the antigen the test is trying to detect is the antibody your body has made in response to the antigen that the virus presents to it during an infection.
Sorry — but sometimes language is used in funny and confusing ways in science. The video below will make it all clear.
Sample: A little blood.
Equipment: These are quite different than the PCR test.
- A sterile workspace (common to both tests).
- An enzyme immunoassay reader, which is a machine that can measure qualities of light (i.e. the intensity of absorbance, fluorescence or luminescence, see video above) which can be indicators of the presence of a particular target molecule.
- Reagents specific to one or more antibody proteins for CoV
- Positive and negative controls.
Detection: Finds antibodies to SARS-CoV-2 in your blood.
Implication: A positive test implies that you were previously infected with SARS-CoV-2 and currently have some level of immunity to it.
When to take it: If you want to know if you are immune to the disease after a confirmed or suspected bout of illness with SARS-CoV-2