The story so far: Since cases of ‘reinfection’ emerged in early January, people who had tested negative for the COVID-19 test again after a while, the question of the latency of the SARS-CoV-2 virus has been the subject of heated debate . The first of these cases arose in the east (China, South Korea), where scientists were puzzled as to why or how people who had tested negative for the virus twice, after a few weeks or months, had tested positive, the second time, albeit with milder symptoms. A latent infection is when the virus in the body is inactive and does not replicate within the host. However, it does possess the ability to reactivate at some point, causing an outbreak of the disease much later.
What is a latent viral infection?
A latent viral infection is an inactive or latent infection, authors Sergey Sheleg and Alexey Vasilevsky write in an article in the World journal of infectious diseases and clinical research. “Unlike active infections, where a virus is actively replicating and potentially causing symptoms, latent (or persistent; but not chronic) infections are essentially static and last for the life of the host and occur when the primary infection is not cleared by adaptation immune response, “they explain. Some examples are herpes simplex viruses type 1 and 2, chickenpox-zoster virus, HIV, Epstein-Barr virus (human herpes virus 4), and cytomegalovirus. They are known to cause typical latent infections in humans, Sheleg and Vasilevsky add.
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They go on to explain that “latent viral infections can be reactivated in a lytic way (replication of a viral genome). The ability to go back and forth from latent infections to lytic infections helps the virus spread from infected individuals to uninfected individuals.” .
Ryan McNamara, a research associate in the Department of Microbiology and Immunology at the University of North Carolina, in a long thread of tweets, tried to explain the difference between the types of viral infections. Tweeting from @Ryan_Mac_Phd, he says: Viruses fall into two broad categories: chronic and acute; while a chronic virus will infect its host for long periods of time, often throughout the life of the host. An acute infectious virus, like influenza and rotavirus, is eliminated from the body after a few days or weeks.
“A chronic virus can go into dormancy. This is when a virus is present inside a cell, but it does not actively produce more infectious virus particles. For example, when a herpes virus infects a cell, its genome can remain in that cell as long as that cell is alive, “says Dr. McNamara.
Reactivation to the lytic state, when the production of new virus particles occurs, he calls an “intentional strategy on the part of the virus to promote its survival.” A perfect example of this would be chickenpox, caused by the human herpes virus 3: after infection, “the body responds and the virus goes into dormancy. Decades later, it can reactivate, resulting in shingles. ” What causes the revival is unclear in this case. According to him, HIV can also go into dormancy after infection. It integrates into host chromatin (a substance within the chromosome) and can be reactivated upon stimulation, such as inflammation induced by infection by coinfecting pathogens. This can lead to uncontrolled replication of HIV and clinical AIDS.
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Does SARS-CoV-2 go into latency? What causes second infections?
Sheleg and Vasilevsky registered South Korean officials who reported that nearly 100 people believed to be cured of the new coronavirus tested positive for COVID-19 again. According to Jeong Eun-Kyeong, director of the Korea Centers for Disease Control and Prevention, the COVID-19 virus may have been “reactivated” in patients rather than re-infected.
Also in Chennai, last week, the civic corps recorded a couple of cases of patients who had recovered from COVID-19 testing positive again after a period of time.
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Professor T. Jacob John, an eminent virologist from Vellore, says: “None of the observations conclusively demonstrates a second infection. In each of these cases, there are sufficient reasons to suspect that it is an infection, with negative results in between. While RT-PCR [reverse transcription/polymerase chain reaction] The tests are considered the gold standard for testing, all tests are not 100% accurate. False positives and false negative results are expected. Patients are known to give negative, then positive, and negative results again, in subsequent tests performed even within days. ”
Dr. McNamara explains the concept of a virus’s “limit of detection” here. This is the threshold where a virus can be detected. A negative SARS-CoV-2 test does not mean zero infection; means there is no detectable infection. ”
Professor John clarifies that another problem is that many viruses can survive at the mucosa level despite immunity. “A classic example is the polio virus, which, like SARS-CoV-2, is also a positive-sense single-stranded RNA (ribonucleic acid). Although immunity begins within two weeks after infection viral clearance can continue for up to 10 weeks, despite very high levels of antibodies. So far, no one has explained why this happens. And, in the case of polio, if a stool test was negative in the medium and then tested positive, we didn’t take it as a second infection, it’s a continuous infection. ” He also discovered through laboratory tests that the host harbors an “antibody-bound virus that is not infectious.”
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Then he adds: “If second infections were common enough, we would have already detected them. But some people may have specific problems with immunity against this virus. In that case, it should be investigated further. ”
Dr. McNamara explains, “It is entirely possible to have a detectable SARS-CoV-2 virus, then not detectable, and then detectable due to the detection limit of our current tests. Also, a SARS-CoV-2 test does not necessarily mean that there is an infectious virus. Tests for SARS-CoV-2 RNA on surfaces can give a positive result, but that simply means that there is some SARS-CoV-2 RNA present, it does not necessarily mean that the RNA is intact or that the RNA is inside an infectious particle. Therefore, the fragmented RNA can actually give a positive result. ”
The Korea Biomedical Review (koreabiomed.com) reported in April that the country’s Central Clinical Committee for the Control of Emerging Diseases had said that the reason why 263 Koreans tested positive after the recovery from the new coronavirus appeared to be not because they contracted the virus again; rather, remaining virus fragments were detected in them.
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Do the test criteria make a difference?
Globally, it is now accepted that clinical signs are sufficient to start treatment for COVID-19, even before an RT-PCR test is performed. Furthermore, the cessation of symptoms is said to indicate that a person has recovered. Unless someone has been seriously ill, the patient no longer needs to test negative twice for COVID-19 to be declared cured or sent home.
“We know that finding cases is now largely determined by evidence in India. But the experience of other nations has shown that we could also do the same with clinical diagnosis, they did not suffer the consequences of that, “adds Professor John.
While 100% protection is not possible, he insists that the use of masks and physical distance will ultimately be the only deterrent to transmission.
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