February 25, 2021

Coronavirus testing methods: How Covid-19 Detects?

As of June 28, the number of patients infected with the new coronavirus Covid-19 is more than Ten Million. The death toll is about Half a Million. Symptoms of this disease are sore throat, cough, runny nose, fever, etc.

But these symptoms are also seen in pneumonia or other lung diseases. So what is the difference between Covid-19? It is not possible to diagnose this disease just by looking at the symptoms.

The number of patients infected with the Covid-19 virus is known through a specific detection test. That test shows who was suffering from this disease. What is that particular test?

The test is the Polymerase Chain Reaction or PCR method. The PCR method is the process of DNA expansion. This process produces a large amount of DNA from a small number of DNA, which can be analyzed to diagnose various diseases.

Carrie Mullis invented the PCR method in the eighties. In recognition of this, he won the Nobel Prize in 1993.

In the PCR method, millions of DNAs are made from tiny amounts of DNA through cyclic heating and cooling. A type of pigment called fluorescent then determines the amount of DNA in the mixture. In this way, the presence of germs in the body can be known accurately.

However, before the coronavirus identification, its genome must be collected. The genome is a single-stranded RNA. It is converted into double-stranded DNA by a type of enzyme. This enzyme is called Reverse Transcriptase or RT. This process and PCR are collectively called RT-PCR.

At present, it is known through RT-PCR whether a patient has the Covid-19 virus in his body or not. This is the only ideal and fast way to differentiate other germs like influenza from the corona. Then let us know the details of how the identification process is done from the patient’s body.

Doctors collecting samples from a patient’s nose in China;
Image Source: AP: Chinatopix

The first step is to collect the patient’s sample. Samples are collected from the upper part of the respiratory tract and the lower part of the lungs.

The surface samples are collected with the help of a soft stick of pure plastic. This is called ‘swab stick’. Swabs are brought from the tonsils to the back of the throat without touching the tongue.

The swab stick is then inserted through the nostrils until an obstruction occurs. Then the stick is turned out for 10-15 seconds. Samples were collected from both nostrils.

After sample collection, the swab stick is sealed in a sterile test tube. It is then sent to the laboratory in a cold box. Samples should be kept at a temperature of 35-40 degrees Fahrenheit. The test is to be done within four days.

The SARS and Mars coronaviruses were collected from lower respiratory tract samples. So it is said to collect samples from this part if possible. In this case, pleural fluid, phlegm are taken as samples in a sterile container.

Nurses, doctors, or staff who collect samples have to take some precautionary measures. They have to use gowns, gloves, eye shields, etc. These are called Personal Protective Equipment or PPE.

Patient sample collectors should use PPE;
Image Source: Robin Lubbock / WBUR

RNA is first collected after the samples are brought to the laboratory. RNA is isolated from human cells, proteins, enzymes. This step is called RNA extraction. If this process is to be done by hand, several chemicals have to be added to the sample. When it is then centrifuged, the RNA is separated from the other parts. Several companies are currently developing one-of-a-kind kits that provide all the tools needed to extract RNA. This can also be done through automatic machines.

The next step in RNA extraction is to add a reverse transcriptase enzyme. This enzyme converts RNA into DNA. This DNA is then placed in a test tube. The test tube mixes nucleotides, DNA-building enzymes, and fragments of tiny DNA. Nucleotides are a structural part of DNA. It contains any one of the four bases of DNA (Adenine, Guanine, Thymine, Cytosine), one molecule of sugar, and one molecule of phosphoric acid. Tiny RNA is mixed with nucleotides and enzymes called ‘primers.’

PCR procedure steps;
Image Source: laboratoryinfo.com

Primers are designed so that they can be matched by finding specific sequences in the virus’s genome. They only combine with the genomes of specific viruses. No other part, such as human cells or bacteria, is attached to DNA.

This process is done on a PCR machine. This machine controls the temperature. When the temperature is raised, the double helix of DNA breaks, and the two strands are exposed. When the temperature is reduced, the primers are attached to the desired location of the exposed DNA strand. In this way, one to two DNAs are formed in five minutes.

When this cycle is completed 30-40 times, billions of DNA copies are produced from one copy of DNA. From this DNA, scientists can quickly identify whether the bacterium has DNA.

PCR machine;
Image Source: istock

Fluorescent dyes are mixed into test tubes to identify DNA. It can be seen only in the presence of DNA. As the number of DNA increases, so does the amount of light emitted. PCR machines have unique types of light measuring instruments. It can detect from a fluorescence pattern which samples contain the virus, which samples don’t. If you have the coronavirus in your body, its RNA will be converted into DNA. These DNAs will then use a fluorescent light to confirm the presence of the virus in your body.

Samples are collected from the patient and sent to the laboratory. The results from the laboratory come to the health workers, then to the patient. In Australia, this process takes 48-62 hours or an average of five days to complete. It takes the same time in other countries. So, the information that we know today was five more days ago. Five days later, the new results showed an increased number of infected patients.

At least 20 companies are currently working to make the virus detection process faster and more automated. The results will be known in half an hour instead of five days. CRISPR-based tests are said to detect the results of viruses as quickly as pregnancy tests. However, these are still in the experimental stage.

Another method is to diagnose antibodies to the virus in the blood. This is called the serological method. It can be used to diagnose antibodies to find out if a person was infected with the virus, but is now healthy. It is cheaper than PCR and can also identify the patient. But it is not as suitable as PCR.

Thanks for reading!

Featured Image: Click Orlando

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