Disease Testing, Prevention And Cure – Perspectives From COVID-19

What began as a handful of mysterious illnesses in the central Chinese city of Wuhan has travelled the world (in less than 80 days), jumping from animals to humans and from obscurity to international news headlines. Today, everything ranging from electronic media, newspapers to social media is overflowing with coronavirus articles. Among them, this is another, which attempts to outline the three significant aspects of an outbreak: diagnosis, medicines and vaccines.

The SARS-CoV-2 (which causes the so-called COVID-19 disease) stands for Severe Acute Respiratory Syndrome Coronavirus 2. As the name suggests, the pandemic causes respiratory illness (like the flu) with symptoms such as a cough, fever, and in more severe cases, difficulty breathing. Before we examine the procedure to develop a vaccine, let us take a look at how patients may be tested for the disease. For this, we make use of three case studies obtained from China, India, and South Korea, starting from the origin of China.

 

Diagnosis

SARS-CoV-2 originated in China around December last year, when multiple patients in Wuhan reported identical symptoms. By the end of January, scientists had access to the virus’ genome (RNA sequence). This genome enabled scientists around the world to move further in creating the necessary raw material required for testing kits. China primarily used real-time RT-PCR kits for testing more than 500,000 people. Here, RT-PCR stands for Reverse Transcriptase Polymerase Chain Reaction.

 

Figure 1: DNA and RNA molecules

The working of kits goes this way: Firstly, healthcare workers gather samples via throat or nose swabs, and total RNA (Fig. 1) is extracted (assuming the virus’ RNA is present in it) from it. This RNA is converted to its complementary DNA (cDNA) by using the reverse process of a natural process known as transcription (giving the term Reverse Transcriptase). In transcription, DNA present inside a cell is scanned to make a messenger RNA (mRNA), an essential raw material in making proteins. 

The Polymerase Chain Reaction takes place after this, which is used to make millions to billions of copies (amplification) of a specific site on a given DNA sample for ease of studying. The obtained cDNA undergoes this reaction which includes primers, short pieces of single-stranded DNA, explicitly designed to attach at the viral RNA sites and initiate the reaction. Along with this, real-time RT-PCR makes use of a special dye (SYBR Green I), which glows only when it attaches to double-stranded DNA. If the viral RNA is present, the primer attaches to it and creates more DNA, thus increasing the glow (since more dye attaches). This indicates the presence of the virus. If  no viral RNA is present, the entire cascade of processes fails at the first step, and hence there is no fluorescent glow. These tests also help in determining whether the viral titre (i.e. the quantity of the virus in the body) is high or low, and accordingly, further curative measures are advised.

India and South Korea use the same technique of RT-PCR in a significant portion of their testing procedures. Another approach is the antibody approach where antibodies to the virus produced by an individual’s immune system are detected. However, this system fails to catch those individuals who have been newly infected with the virus and haven’t developed an immune response, or the elderly who aren’t able to mount a sufficient immune response.  

Let’s now take a look at the road ahead with regards to various curative approaches to combat the disease and vaccines to prevent it.

 

The Curative Approach – Drugs and Plasma Transfusion

One of the biggest rumours surrounding the effectiveness of a combination of anti-malarial (hydroxychloroquine/chloroquine) and antibiotic (azithromycin) drug needs to be cleared. The efficacy of these drugs on a small group of patients does not make them a cure. Malaria is caused by a parasite, while azithromycin is an antibacterial drug. Since a virus causes COVID-19, no theoretical or conceptual link justifies the widespread use of these drugs. These drugs might be curing individuals via complex interactions with each person’s immune system, and this is largely a trial-and-error approach. While these approaches are often the only way out in a crisis, it is imperative to state that there isn’t a definitive cure for COVID-19, and we must still take the utmost precautions. 

Other drugs that have proved to be effective against the coronavirus family (SARS & MERS) include Remdesivir, which was earlier rejected as a drug against the deadly Ebola virus and generic antiviral medicines. Let’s now understand how each of the drugs work, shall we?

An understanding of the viral life cycle is essential to grasp the mechanism of these drugs. On entering the body, a virus attaches to a specific body cell that has complementary receptors (like a lock and key). Then it releases all its genetic material (in this case, RNA) into the host cell so that it can be processed to create more viruses. The genetic material goes inside where it is translated (scanned by cell structure known as ribosome) to form a protein which further ensures the production of virus. The virus then exits this host cell taking along with it a part of the cell membrane (for protection) and destroying the cell itself. The new virus now infects another healthy cell, and the cycle keeps repeating. Antiviral drugs arrest this viral replication cycle at any one or more steps, thus bringing down the entire viral operation.

 

Figure 2: Viral Replication cycle

 

Anti-malarial drugs increase the acidity of the cell surface, making the virus unable to inject its genetic material into the cell. Apart from this, they can also trigger a robust immune response. Remdesivir instead acts as an RNA itself (a nucleotide analogue), attaching itself to the viral RNA and stopping the protein from being formed. If there is no protein, then no more viruses can be created, thus curing the patient. However, it must be noted that this information on drug action is based on elementary studies; scientists are still looking for more detailed explanations.

An excellent non-drug based approach has been proposed in China, which is called the Plasma Transfusion technique. In this technique, the plasma from a recovered patient is injected into a severely ill one, to trigger what is called “Passive Immunity.” Plasma (of the recovered patient) possesses antibodies which were used by the infected person’s body to eradicate the virus. But this has some limitations, because we need to ensure that the number of antibodies is enough to wipe out the virus (a time and labour intensive process). Moreover, the plasma must not contain any coronavirus because that would make the situation worse. A study conducted on five severely ill patients in Shenzhen, China, has proved to be successful as their condition has improved post-transfusion. While the cohort is small, there is less skepticism about the study results because the method (otherwise known as convalescent plasma) has worked well for other conditions.

 

Figure 3: Plasma transfusion technique

 

A Preventive Approach ala Vaccines

A more permanent solution would be to let the body make its antibodies itself: known as vaccination. Quantity isn’t an issue here because the body makes sure that antibodies are prepared until the virus is eradicated. While this is the best possible method, it is the toughest as well, not only for the novel coronavirus but for any disease. Let us see why.

Vaccine development takes place primarily in 2 steps, each involving multiple phases. The first step is the pre-clinical development in which research is carried out in labs using animals. To make a vaccine, scientists use the virus itself in a deactivated or inactive state. This harmless virus, when injected into the body, forces the immune system to make antibodies (the weapons). Every step must be performed with utmost preciseness and patience. The cultivation of viruses in laboratory conditions is the first step, followed by deactivation to make it harmless. If the deactivation isn’t done correctly, the virus can cause even more problems than before. Even if scientists succeed in preparing a proper sample for injection, human trials are the most extended component in this process. Testing begins from small-scale trials and eventually goes to large-scale testing of around 100 people, taking approximately 12 months. In this period, if the trials go wrong even at a single stage, the vaccine is disregarded immediately. Hence making a vaccine for any disease is very challenging and requires rigorous testing.

For coronavirus, scientists are looking at an alternative method known as Vaccine Rapid Response Platforms, in which the scientists jump the stage of creating the virus itself hence cutting down on the total time required. In this, scientists make use of the virus’ genome, identifying the site of messenger RNA (mRNA) and injecting it in the body, making the healthy body cells produce antigens (the non-harmful parts), which are replicas of the ones present on the virus’ surface. These antigens stimulate the body’s immune system to make antibodies. Moderna Inc., USA, and the University of Queensland, Australia, are two organizations being funded by the Coalition for Epidemic Preparedness Innovations (CEPI) who have successfully come up with vaccines (already in the testing stage) based on the method discussed. We could be seeing a potential vaccine candidate from either of the two very soon.

Diagnosis kits, therapeutic drugs and vaccines are the most critical components to combat this virus, but the resources are finite. This scarcity is the reason we should do everything in our control to prevent the spread. The country, on the whole, will face severe problems of shortage if we don’t make sure that unnecessary cases are avoided. This means that by staying inside and washing your hands, you’re not only protecting yourself but also providing resources to those who have already been infected.

 

References

https://time.com/5807669/coronavirus-vaccine-moderna/

https://timesofindia.indiatimes.com/city/jaipur/city-docs-cure-corona-patient-with-hiv-drugs/articleshow/74584859.cms

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5844999/

https://www.businessinsider.in/science/news/11-extreme-measures-china-took-to-contain-the-coronavirus-show-the-rest-of-the-world-is-unprepared-for-covid-19/articleshow/74660747.cms

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