As the world looks for answers to fight the pandemic, two potential treatment and testing procedures which have come to light are Convalescent Plasma therapy and Rapid Diagnostic Testing
The Coronavirus has brought the world to a standstill and doctors and scientists are working overtime to develop vaccines/drugs and new treatment strategies to cure patients. Two such potential treatment and testing procedures which have come to light are Convalescent Plasma (CP) therapy and Rapid Diagnostic Testing (RDT).
In order to understand CP, it is essential to grasp the concept of antigen-antibody. If any thief tries to come inside your house, your defence mechanism will kick in and you will either stop him or he will be successful in robbing you. However, in the process of defending the house, there is bound to be some damage to it. Then, you will call the police in order to get the thief arrested. In the long-term, you will get a burglar alarm system or CCTV camera installed. This will burglar-proof your house.
Now, apply this allegory to the human body. The thief is the Antigen and your response is what the body does to these Antigens with the aid of antibodies. There are various types of antibodies, like IgM, IgG, IgE, IgA, IgD. Your initial response is similar to the IgM which is the first antibody to respond to any antigen. The long-term measures you have taken is IgG and the collateral damage to your house is akin to inflammation that manifests as fever, swelling, redness and pain.
Just like you don’t react adversely to everyone who enters the house, the same way your body does not react adversely to self-Antigens. But if you spot the same thief you become vigilant and try to take evasive action before he harms your home further. The body reacts in the same way to any Antigen that has already been contained by it by producing antibodies. If the Antigen is re-introduced into the body, its response is intensified. This is why if you have chickenpox once, you don’t get it again. This principle is used in creating an “active” vaccine, where a small quantity of infection (Antigen) is introduced into the body so that antibodies are produced and provide protection to the individual against the infection.
However, there is also a “passive” type of vaccine under which pre-prepared antibodies are given to a person. However, the immunity acquired by this vaccine is not life-long and once these antibodies given from outside are used up, they no longer provide protection. Since the antibodies were not produced by the body originally, the number of antibodies in the body is not adequate to neutralise any antigen which enters it in the future. This is the reason people need to get tetanus injections repeatedly. The CP therapy is a process in which the antibodies from the plasma (the largest part of blood, which when separated from the blood is a light yellow liquid) of a recovered patient of COVID-19 is transferred to a patient who has an active Coronavirus infection, with chances of it worsening. This is a type of passive immunity only, in which a patient battling the infection is assisted by someone. CP therapy had been previously used for SARS and influenza and has shown positive results. However, the results of CP therapy in Coronavirus are variable and still evolving. Trials conducted on 10 COVID-19 patients given CP therapy in China showed positive results. A task force created by Kerala has got permission from the Indian Council of Medical Research (ICMR) to conduct further research on it. The ICMR is also not planning to conduct it for all patients but select ones and this will not be a treatment per se but a clinical trial. However, if approved and successful, it will be scaled up to a treatment.
The antibodies are proteins formed by B-Lymphocytes and they are part of Humoral Immunity. There is another system called Cell-Mediated Immunity, in which major work is done by T Lymphocytes. However, CP therapy requires further research (it has been approved by the US FDA) and also requires monitoring while transfusion of the plasma into another patient as there can be life-threatening reactions. Hence, careful monitoring and a due call need to be taken by doctors and researchers on the use of CP therapy. RDT has become a very important strategy to contain the spread of the Coronavirus. In this, confirmatory testing is by RT-PCR (reverse transcriptase Polymerase Chain Reaction) in which absolute confirmation is provided as the presence of RNA of the virus is demonstrated in the nasopharyngeal and oropharyngeal swabs. However, this is costly and time-consuming and hence there is a need for the development of RDTs. These RDTs work in two ways. One is the demonstration of the protein (antigen) of the virus from the respiratory tract of the individual and second is the demonstration of antibodies in the blood of the person suspected to be infected by the Coronavirus.
In the first type, there are specially made paper strips on which antibodies to the Coronavirus are affixed and this is enclosed in a plastic casing. So, if a person’s respiratory tract sample has the antigen of the Coronavirus then there will be a detectable signal in 30 minutes. These antigens, which are detected are only expressed when the virus is replicating i.e it is in the active stage of infection. However, these factors depend on many other factors. The World Health Organisation (WHO) says, “How well the tests work depends on several factors, including the time from onset of illness, the concentration of virus in the specimen, the quality of the specimen collected from a person, how it is processed and the precise formulation of the reagents in the test kits.” (MR, Inputs: Agencies).