Written by Liza Farrugia

It should be no surprise that millions of swab tests are carried out across Europe on a daily basis. These tests are used to diagnose infected patients and have become essential to the effort to combat the disease. However, some might find it hard to blindly trust the accuracy of such tests without understanding how they actually work to provide positive or negative results.

Virus structure and spread

Firstly, it’s important to distinguish between the disease and the virus. The coronavirus disease (COVID-19) is caused by the virus officially named ‘Severe Acute Respiratory Syndrome Coronavirus 2’ (SARS-CoV-2), otherwise referred to as the “COVID-19 virus”. This virus is genetically similar to SARS-CoV-1 (the virus responsible for the 2002-2004 SARS epidemic) but has structural differences as well as a higher reproductive number which may explain its enhanced rate of transmission.^[3]

SARS-COV-2 vs SARS-CoV-1

After initial exposure, symptoms typically develop within 5-6 days and the SARS-CoV-2 load in the respiratory tract peaks at the time of symptom onset or within the first week of illness. This means that it is most contagious just before or within the first 5 days of symptom onset and patients whose symptoms have not yet appeared still carry large amounts of the virus in their upper respiratory tract. Contrastingly, SARS-CoV-1 is most contagious during the second week of illness as opposed to the first week, thus enabling early case detection and minimising spread. Additionally, symptomatic and pre-symptomatic transmission likely plays a greater role in the spread of SARS-CoV-2 than asymptomatic transmission.

Explained: Testing methods

PCR Swab Test

Currently, the main diagnostic test for SARS-CoV-2 is the nucleic acid test which uses reverse transcription polymerase chain reaction (RT-PCR) technology to detect viral RNA in the sample. A swab is used to collect mucus from the nose or throat and the sample is then sent to a lab to be tested. To perform RT-PCR, first chemicals are mixed with the swab in order to extract the genetic material (RNA) of any virus present. Reagents called primers and probes are then added to the sample, which undergoes several controlled heating and cooling cycles in a specialised machine to convert the viral RNA to DNA and then amplify the DNA.

Results are interpreted through fluorescence – probes which emit a strong fluorescent signal on binding to the DNA. If there is a SARS-CoV-2 infection the machine will detect the fluorescent signal. RT-PCR technology can detect SARS-CoV-2 RNA in the respiratory tract for an average of 17 days. However, such samples have rarely been found to be positive beyond 9 days of infection, due to decreased levels of  viral RNA.

Antigen Swab Testing

Another form of diagnostic test is antigen testing, commonly known as rapid tests. While the RT-PCR test looks for viral RNA, antigen testing works by detecting specific proteins on the virus surface. Both testing methods make use of nasal or throat swabs to diagnose an active coronavirus infection. Antigen tests are also known as rapid tests since results can be obtained within an hour, whereas RT-PCR test results can take up to a week. Antigen tests are more likely to miss an active coronavirus infection than RT-PCR tests and so negative results may need to be confirmed with the highly accurate RT-PCR test.

Antibody Tests

In response to a threat such as SARS-CoV-2, the body’s immune system makes specialised proteins known as antibodies to fight infection. Antibody tests, also known as serology tests, use blood samples to detect the presence of these specific antibodies produced, and not the virus itself. Since antibodies take several days or weeks to develop after infection and remain in the patient’s blood for weeks after recovery, an antibody test cannot diagnose an active coronavirus infection but shows if you’ve had the disease in the past.

As of 28^th October 2020, the EU Commission decided on additional COVID-19 response measures, including establishing more effective and rapid testing to help combat rapid transmission. Thus, under the Emergency Support Instrument, the Commission is mobilising €100 million to directly purchase rapid antigen tests and deliver them to member states.

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Written by the MBSA Executive Team

What are Genes?

DNA (deoxyribonucleic acid) is hereditary material in humans which is found in the nucleus of a cell. It takes the shape of a twisted ladder and the “rungs” are made up from 4 bases -adenine, guanine, cytosine and thymine – which are used as the basis of the genetic code. In humans it is the sequence and order of these bases which makes us all different.These sequences give rise to genes. Genes are segments of DNA that will code for a specific protein within cells in the human body. Genes are stored in chromosomes and inherited. Physical features are determined by your genes, so if a gene mutates, it may change the trait in codes for. These mutations are transferred from one generation to another, and thus can be used to provide a better understanding of past population processes.

Some Genes Facts and History

In the past, Europe’s royal families had a lot of inbreeding. This resulted in the rarer mutations found within the family itself being more common, thus increasing the chances of the future generations having that mutation. For example, Queen Victoria carried the gene for haemophilia, which is the prevention of effective blood clotting. She married her first cousin, who also carried this gene. As a result, their children had a high likelihood of also carrying the gene, causing it to spread to the rest of European royalty, namely Russia, Spain, and Germany.

What is Genetic Mutation?

Genetic mutations are often studied in the lab through bacteria. Bacteria are single-celled organisms that have their DNA roaming freely in their body. They are commonly used in the lab because they are easy to work with and their genes can easily be mutated . Their DNA is mutated through a specific type genetic material known as a plasmid. Plasmids are small pieces of circular DNA which do not form part of the cellular chromosome and hence performs independently of the chromosomal DNA allowing independent replication. These have been exploited through biotechnology whereby plasmids can be designed and created in the lab and hence be encoded specifically to contain certain proteins or antibacterial strains of interest.

This has been done for generations for the production of human insulin in bacteria and can be done to make bacteria glow.

How to Make your Genes Glow

Green Fluorescent Protein (GFP) is protein that, as the name suggests, glows green in visible and UV light and is taken from a species of  jellyfish known as Aequorea Victoria. The gene coding for GFP can be included within a plasmid and inserted into bacterial cells to make it glow by reading the plasmid as its own and producing the protein. 

The genetic mutations do not always take. To to eliminate the problem of separating glowing and non-glowing bacteria, the plasmid also typically contains a gene for antibiotic resistance. This antibiotic-resistance will only be characteristic of the successfully transformed bacterial cells, which have taken up the foreign DNA. Therefore, upon growing the bacterial culture in the presence of that particular antibiotic, only the plasmid-transformed cells survive, indicating the effectiveness or otherwise of the genetic modification process .

In addition to antibiotic resistance, the successfully transformed cells also exhibit fluorescence, as a result of GFP protein expression. Since the GFP protein exhibits green fluorescence in exposure to UV light, bacterial growth may be monitored by the number of visibly fluorescing colonies. Bacterial cells which have remained unmodified do not survive as they are not immune to the antibiotics present around them.

What’s the Use?

As fascinating as it may be to make bacteria glow, it wouldn’t be common lab practice if it didn’t have any further applications. The most common use is as a visual tagger. Many genes and proteins under research do not have visual indicators that they are present within a cell. By coupling the GFP gene on the plasmid with the gene of interest you can conclude that any bacteria that glow also has the other gene!

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