22 Jun 2020
In this COVID-19 pandemic, the importance of testing for viral infections has been emphasized more than ever before. However, have you wondered about how these viral tests actually work?
It turns out that there is not one but several viral testing methods, including but not limited to molecular/genetic tests (polymerase chain reaction and isothermal nucleic acid amplification), antibody tests, and antigen tests. Now, don’t get overwhelmed with that jargon and read on to find out more about those aforementioned tests!
Before we delve into testing for viruses, let’s understand the structure of a virus. Most viruses contain three basic components: a capsid (a hard protein shell of a virus enclosing the genetic material), envelope/surface proteins, and genetic material (DNA or RNA and unique to every strain of a virus).
Magnify this further and you’ll see that the genetic material is made up of thousands of five different types of nitrogenous bases (adenosine, cytosine, guanine, thymine, and uracil).
But, how can scientists use these bases to their advantage for testing? Well, unless the strain of the virus is mutated, the sequence of these bases is the same for every strain; therefore, scientists can identify the particular sequence of bases of a virus and test for the same in patients.
Now that the basic composition of a virus is clear, let’s look at the various testing methods, beginning with molecular tests. Molecular tests are the most accurate and widespread tests currently available. These molecular tests, as seen before, rely on identifying the specific base sequences in viruses.
To conduct molecular tests, doctors must first obtain a sample of mucus or another bodily fluid (recall those images of doctors using swabs to obtain saliva from patients’ throats!). However, even if the virus is present in the sample, it is not enough to accurately study, as the virus could hide in plain sight.
Therefore, the sample must be copied, thus amplifying the virus. This can be done through two methods: polymerase chain reaction (PCR) or isothermal nucleic acid amplification (INAA). To conduct PCR, scientists extract a small portion of the genetic material and replicate it to make sufficient copies, and then use the same to conduct tests. On the other hand, INAA is a faster method to conduct amplification, but is not as widely used as PCR.
However, while molecular tests are accurate, they are often very slow. To increase testing speeds and capabilities, methods like antibody testing and antigen testing can be implemented.
Let’s look at antibody testing first. When a virus enters your body, your body reacts by creating antibodies to fight the same in the blood. Therefore, with antibody tests, the presence of antibodies in your blood is tested for, which comes up regardless of symptoms. However, due to the varying times at which different types of antibodies are produced (which also differs depending on the virus), antibody tests may not be the most reliable. Antibody tests are also used to test for past infections.
Moving on, antigen tests follow a similar process by taking blood, but they look to identify antigens (proteins secreted by the virus) instead of the antibodies.
Thus, there are several methods of testing for viral infections and each method has its own pros and cons, so there is no one short-stop answer to this curiosity. Which method do you think is the most effective?