Importance of Diagnostic tests for detecting infectious diseases like COVID-19
The search for rapid diagnostic tests has become a joint action of companies developing antibody tests in response to the Covid-19 pandemic. As the new controls are forced, the competition to create and finish these kinds of assessments increments. Nonetheless, there are still some specialized inquiries regarding upgrading the test configuration, essentially to see how the viral covering triggers the acknowledgment and balance of the infection by a sound immunity system.
Why are antibody tests necessary now?
The situation that opens up now is realizing how to recognize what sort of tests are the best in this battle against Covid-19. On the off chance that a test can show that a medical care proficient has effectively had Covid-19 and is consequently likely invulnerable, they can get back to work unafraid of disease.
In this sense, the multipurpose nature of these tests is analyzed. On the one hand, verify that vaccines work as intended during clinical trials. By measuring antibody levels in infected and recovered patients, we will have a much better idea of the levels of protective antibodies that a vaccine needs to elicit; on the other hand, they are used in contact tracing long after the infection is suspected of an individual.
PCR tests that detect viral RNA indicate a current viral infection. Currently, they are being used by many antiviral testing lab to diagnose Covid-19 cases and are an essential part of tracing and contact testing. However, given what is happening, the challenge is to supply all countries. The problem is that there is an excess demand for PCR primers and positive controls, which are necessary to guarantee the performance of individual machines.
Antibody tests are different because they require some knowledge of the proteins that make up the viral load; specifically, those proteins to which the immune system responds, triggering the production of antibodies that signal or neutralize the virus. Some diagnostic companies are cautious about giving too much detail, although the spike protein is universally perceived as the best candidate. The spike protein research also presents pathways for the development of therapies against Covid-19.
MOLECULAR TESTS IN THE DIAGNOSIS OF COVID-19
The molecular test used throughout the world for the direct detection of infection with SARS-CoV-2 is the RT-PCR test on the genes expressed by this virus. Liu et al. analyzed, through RT-PCR, the gene expression of SARS-CoV-2 fragments from sputum, bronchoalveolar lavage, and respiratory tract swab samples from 4880 patients with symptoms of respiratory infection or close contact with the virus in Wuhan hospital. The ORF1ab gene fragment and a nucleocapsid protein (NP) fragment were sequenced. For a confirmatory diagnosis, the authors considered SARS-CoV positive patients who presented both gene fragments. For sputum, the NP fragment was expressed in 49, 12% of patients while the ORF1ab fragment was 50.88%, and the percentage of patients who said both fragments was 49.12%. In bronchoalveolar lavage, the NP fragment was expressed in 80% of patients, while the ORF1ab fragment in 100% and the percentage of patients who expressed both fragments was 80%. In the respiratory tract swab case, the NP fragment was expressed in 39.8% of patients, while the ORF1ab fragment in 40.98% and 38.42% of patients said both fragments. These results found that the most exposed patients are adults over 70 years of age with 61.81% incidence. On the other hand, a group of patients had some symptoms associated with the corona virus, but they were discarded since their results came out negative.
SEROLOGICAL TESTS IN THE DIAGNOSIS OF COVID-19
Molecular and cellular element of the innate and acquired systems is involved in the antiviral immune response against viruses that affect the respiratory tract, including SARS-CoV-2. These include molecular mediators such as type I interferons and IgA, IgM, IgG antibodies, neutrophils, macrophages, and lymphocytes with cytotoxic activity on infected cells, such as natural killers and CD8 + T’s. Additionally, dendritic cells and CD4 + T helper lymphocytes are highly relevant in activating the effective immune response. Specifically, antibody secretion is a very relevant and simple to detect indicator that reflects the immune response against viral antigens.
Rapid serologic tests are simple and very easy to perform lateral flow immunochromatographic or immunoassay tests that detect antibodies to the virus in one step. Serum, plasma, or whole blood samples can be used for these tests. These rapid tests are complementary and are not a substitute for detecting viral genetic material by RT-PCR. In this sense, one of the limitations of diagnosis based on the detection of specific immunoglobulin’s for a particular antigen is the difficulty of knowing with certainty when these immunoglobulins appear in blood samples, which could lead to a false-negative diagnosis.
GOOD PRACTICES IN THE COLLECTION AND HANDLING OF SAMPLES FOR THE DIAGNOSIS OF COVID-19
Biosafety is an essential aspect that must be considered during collecting and handling the sample required to diagnose COVID-19 disease. WHO recommends level 2 for diagnostic testing. Antiviral microbiological testing lab personnel must have specific training in the management of pathogens, under the direct supervision of a competent researcher, according to the biosafety standards of each laboratory.
The safety protocols for obtaining, transferring, handling, and using the sample are of utmost importance to provide accurate and interpretable results. Complementing the strengths of molecular tests that allow the specific detection of SARS-CoV-2 with immunological tests that assess the host’s immune response will be crucial for the accurate and timely diagnosis of patients. Additionally, these same techniques offer alternatives for determining molecular markers with predictive value, which will be especially valuable to differentiate the management of patients less than 60 years of age without pre-existing co-morbidities.