Test, test, test. This has been one of the slogans repeatedly enunciated by the World Health Organization. In fact, one of the ways to stop the spread of the new SARS-CoV-2 coronavirus, which causes COVID-19, is to detect the lesions as quickly as possible. infected people and isolate them in order to stop transmission in the community.
What tests are there for this purpose? There are at least three tests to detect the presence of the new coronavirus.
One detects your genetic material, another detects the presence of antibodies that have been produced by the immune system of an infected person, and a more recent third detects small viral particles (eg protein capsid spikes) that are called antigens, for being able to trigger an immune response in the host.
About two weeks after SARS-CoV-2 was first identified in China, Chinese scientists were able to map the genetic code of this new coronavirus.
This knowledge, which was shared worldwide in the foreshadowing of unprecedented scientific collaboration on a global scale that has taken place, allowed, almost immediately, to develop a molecular biology test which makes it possible to detect the presence of genetic material from the virus in the human body.
Scientists were prepared to do this, as the underlying detection strategy had been developed for other viruses for decades, based on the use of the bioanalytical technique of PCR (English acronym for the polymerase chain reaction, developed in 1983 by Kary Mullis, the which won him the Nobel Prize in 1993).
How does this test work? With the help of an appropriate swab, a sample of secretions and epithelial cells is taken from the suspect's nose or back of the throat. The swab with the biological exudate sample is placed in a suitable and sterilized tube, which contains a solution that prevents its degradation.
The tube with the sample is then sent to a certified laboratory, where a treatment will first be carried out to inactivate any viruses that may be present. This is important to prevent contamination accidents from happening to laboratory personnel.
Afterwards, the content of the sample is treated with its own reagents that extract the genetic material that exists in the virus (in the case of SARS-CoV-2, the genetic material is made up of a single strand of RNA).
As the genetic material will exist in small amounts, it is necessary to amplify it so that it can be detected, if eventually present. And this is done through the polymerase chain reaction (PCR), a cyclic process that can take several hours.
At a certain stage of this process, a fluorescent marker that binds to the genetic material is added. The result is then analyzed by measuring the fluorescence present. If this has a certain significant intensity, this indicates that there were coronaviruses in the sample taken from the person tested and that he is infected with active viruses. The test is then said to be positive.
It should be noted that, as in all laboratory tests, this one also presents a certain uncertainty, which can reach, according to some recent studies, up to 11%. In other words, out of 100 tests performed, 11 could be false positives or negatives. But it is the best we have so far in molecular biology tests to directly detect the presence of SARS-CoV-2 in a given person.
The second type of tests referred to is the one called serological test. The purpose of this test is to try to identify the presence of antibodies that have been developed by the immune system of a person who has been infected with SARS-CoV-2.
This type of test is most useful at a later stage of the infection, as the immune system of a “normal person” “needs” about 5 to 10 days after infection to produce enough antibodies to be detected from quantitatively or qualitatively.
The analysis in this type of serological test is faster than the type of test described above, it does not need to be carried out in a molecular biology laboratory and can generate results in about less than an hour. These are so-called quick diagnostic tests!
When performed on a representative sample of the population, this serological test can provide information on the rate of exposure to the virus of a population and, consequently, serve as a basis for knowledge of the epidemiological evolution of the disease and thus scientifically and adequately guide health authorities in the their efforts to alleviate or increase measures of social confinement.
This test is performed using a small blood sample from a person. The tests are designed to detect the presence of specific IgM and IgG antibodies to SARS-CoV-2.
In a very simple way, we can say that the presence of IgM-type antibodies means that the person is still at an early stage of the infection, while the presence of IgG-type antibodies and the absence of specific IgM for this coronavirus may indicate that the person has had contact with the virus but will no longer be infected.
Regarding COVID-19, this pattern of seroconversion between IgM and IgG is not yet fully established, and it is not known how long IgG-type antibodies remain in the body and confer a potential natural immunity against SARS-CoV-2.
The accuracy of this type of serological test continues to be studied, considering both its sensitivity in detecting infected people and its specificity to circulating strains of SARS-CoV-2, which affects the percentage of false positives and negatives.
O third type of test above was developed even more recently and detects, more quickly than the first, the presence of the virus in an eventually infected person.
An exudate from the nose or the back of the throat is then swabbed. The sample is subjected to a treatment in order to fragment any virus proteins that may be present.
The resulting viral protein fragments are then tested by interaction with monoclonal antibodies specifically developed to SARS-CoV-2 antigens.
This type of test can be performed outside the laboratory, for example in a doctor's office or in a hospital triage, the qualitative result (positive or negative) is obtained in about 15 minutes and gives an indication of whether the person is, or not, infected with the new coronavirus.
Despite being much more imprecise than the molecular test that identifies the presence of genetic material, this type of test for the presence of viral antigens has the advantage of being quick to immediately isolate a potential suspect.
A positive result may have to be confirmed by genetic testing and is not a sign of immunity to SARS-CoV-2.
These rapid diagnostic tests, less costly also because they do not require molecular biology laboratories and can be performed by non-specialized personnel, although less accurate, can be essential and valuable tools in monitoring the exposure and circulation of the SARS-CoV-2 virus. in the community and allow to assess the much desired “group immunity” of a given population.
Finally, and for now, to say that these five months of pandemic "coexistence" with this new disease allowed us to learn to understand it and treat it better on the hospital front, even without specific medications and in the absence of an efficient vaccine and protective, which may take some time to be available, despite the enormous efforts of interlaboratory cooperation at world level.
We have to learn to live with this virus that, everything indicates, will become endemic, it has come to stay with us, in a difficult balance between prevention through the precautionary principle and the reestablishment of a normality of social coexistence.
Science is giving and will give the safe answers, which politicians need to base their public health decisions, but, for that, it needs time to correct any errors and dispel doubts and uncertainties inherent to the scientific method itself.
It is necessary to be humble and say that there are still many things we do not know about COVID-19 and the future evolution of the pandemic.
Protect yourself and protect others. The pandemic is not over yet!
Author Antonio Piedade
Science in the Regional Press – Ciência Viva
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