If viruses could be defined by a single characteristic, objectivity would be a good option. After all, its objective is quite simple: to invade the cells of a living being and use them to create new copies of itself, which will repeat this process.
Usually, the rite of invasion and replication lasts a few days, and if the immune system is unable to deal with the problem, the condition becomes more serious and life-threatening.
But there is a group of viruses that go one step further.
Shortly after the initial infection, They manage to hide in some corner of the body.
This phase can last for months, years, or even decades, and only ends when defense cells stop working as expected.
Then the infection comes back and causes health problems again.
And this group has several well-known representatives, ranging from HIV, which causes AIDS, even herpes simplex 1 and 2, which cause sores at the corner of the mouth and in the genital region.
But, how do they manage to go unnoticed? And how do they reappear after so long? Could this be the case for SARS-CoV-2, the coronavirus responsible for covid-19?
Basically, there are four ways in which a virus hides in the body.
The first of these is frequently used by the herpes family.
In addition to herpes simplex virus type 1 and 2, it includes chickenpox, and Epstein-Barr, which is behind the “kissing disease”, among others.
“They have DNA as genetic material and manage to stay in the nucleus of the cells, like a appendix to our own genetic code”, explains the virologist Décio Diament, from the Hospital Israelita Albert Einstein, in São Paulo.
It is worth remembering here that DNA is the set of letters (known in science as nitrogenous bases) that make up the genome. They are “lined up” in two strands, usually in the classic double helix format.
“These viruses of the herpes family remain dormant for a long time, without replicating very intensively. They manage to inhibit the internal defenses of the cells and become ‘invisible’ to the immune system”, adds the doctor, who is also a consultant to the Brazilian Society of Infectious Diseases.
RNA viruses
The second mechanism it is commonly used by another family: retroviruses such as HIV and HTLV.
It is important to mention that this duo does not have DNA, but RNA.
In other words, your genetic information is organized in a simpler wayin a single strand of nitrogenous base sequences.
retroviruses they can merge with our genetic code.
This integration most often occurs in T cells and macrophages, two important parts of the immune system.
But, how do they accomplish this feat, if we are talking about RNA viruses and we are based on DNA?
Both HIV and HTLV have an enzyme called reverse transcriptase.
And this means that can convert the genetic code de these viruses from RNA to DNA.
With this, they are able to embed itself in the human genome and remain hidden for a long time.
“This represents a great difficulty, because we cannot eliminate them even with the available drugs,” explains Dr. Estevão Portela Nunes, deputy director of clinical services at the National Institute of Infectious Diseases of the Oswaldo Cruz Foundation (INI-FioCruz), in Rio de Janeiro. janeiro.
In other words, the antiretroviral cocktail used in HIV-infected patients can even inhibit viral replication. However, if the person stops taking the medication, there is a risk that HIV will become active again.
Sanctuaries and other mysteries
The third option for hiding some viruses are the so-called immunoprivileged sites.
These are regions of the body that the immune system cannot access as easily, such as the testes, eyes, and central nervous system (spinal cord and brain).
The action of defense cells is limited in these areas to prevent the inflammatory process, that occurs when they fight an infection, damage more sensitive structures, such as the nerves and the reproductive system.
If, on the one hand, this represents a form of protection for one’s own bodyon the other hand, creates a kind of “sanctuary” for some viruses to thrive for a while longer.
Work published in recent years has found zika and ebola in semen of patients, for example.
Immunologist Daniel Mucida, a professor at Rockefeller University in the United States, says that the fact that the virus is found in semen or other parts of the body does not necessarily mean that is active and may cause problems in the future.
“The impact of this viral persistence is not yet clear,” he says.
And, as far as is known, the permanence of viruses in such sanctuaries does not last that long.
Within a few months, even with the most limited access, the immune system can eventually eliminate to the invaders.
There is still a fourth group of viruses capable of prolonging their stay in the body, even outside immunoprivileged sites.
“This is the case of respiratory syncytial virus, which can persist in the lungs and is associated with chronic inflammation, especially in children, and chikungunya viruswhich remains in muscles and joints,” says immunologist Carolina Lucas, a researcher at the Yale University School of Medicine in the United States.
Scientists are still studying why this happens in some patients (and not in others).
immune stumble
Although it may seem that all of these viruses are dormant and no longer a cause for concern, some of them “wake up” after a few years (or decades).
“When the immune system makes a mistake for some reason, these pathogens can resurface and cause problems,” explains Diament.
This “error” varies from infection to infection.
In the case of herpes simplex, if the infected individual spends many hours in the sun or is in a very stressful time in your lifethis may be enough for lesions to break out.
In other situations, the body’s own natural aging leaves room for some infectious agents to wake up.
The classic example of this is varicella-zoster, a virus that causes chickenpox (usually in childhood) and has been hidden in the body for decades.
Later, after the age of 50 or 60, this pathogen can reappear and cause a condition called herpes zoster or shingles, characterized by very painful blister-like lesions on a strip of the body (usually on the trunk or abdomen).
Today, there is even a vaccine indicated for these older people.
And there are, of course, a number of other conditions that impair the action of the immune system and can serve as an opportunity for viruses.
“This includes serious accidents and injuries, major surgeries, transplants, tumors, pharmacological treatments and other serious infections”, lists Diament.
In these cases, doctors are already monitoring them and can provide treatments to minimize the damage.
Finally, it is also worth remembering that some pathogens are related to diseases that are not always related to the initial manifestations of the infection.
This is the case for some hepatitis virus, that can cause liver cancer, HPV, which is behind several types of tumors.
Or also from Epstein–Barrwhich has recently been linked to multiple sclerosis.
And the coronavirus?
Given such a diversity of viruses, could SARS-CoV-2, which causes covid-19, persist after the initial infection?
The experts consulted by BBC News Brazil they consider it unlikely that they have or develop this capacity.
“SARS-CoV-2 is an RNA virus that does not have that reverse transcriptase enzyme, like HIV, so it cannot be integrated into our genome,” explains molecular biologist Carlos Menck, from the Department of Microbiology of the Institute of Biomedical Sciences from the University of São Paulo (ICB-USP).
As well lacks DNA in its constitution, as occurs with viruses of the herpes family, which prevents their prolonged persistence in the cell.
“And the cases that we see now, of people who have covid again, happen because they were infected with the coronavirus for the second time, and not because it was hidden in their body for months,” explains the specialist.
“If we found something different than that with the covid virus, it would be a big surprise for us.”
But, how to explain the cases of long covid, in which individuals have discomfort for months, even after recovering from the initial discomfort?
Diament clarifies that this phenomenon seems to be more related to the response of the immune system to the invasion of the coronavirus.
“In some patients, covid causes real damage that can last for months and is manifested through fatigue, difficulty concentrating, loss of smell…”
“This seems to be a consequence of the inflammatory process that occurs during the first days of the infection. In some cases, the immune system reacts violentlyand the effects of this can be prolonged, ”explains the doctor.
Lucas and Mucida say, however, that in these cases the persistence of some viral components, such as protein and RNA fragmentsin the organism.
“There is evidence pointing to both sides, including the observation of viral RNA in regions such as the intestine for a long time”, they point out.
It remains to be seen whether these small virus fragments would be able to keep the immune system on alert and cause damage for weeks or months or if they are just a finding with no practical effect on people’s health.
But, as Portela Nunes, from FioCruz, points out, in the case of covid-19, we already have at least one piece of good news: “Vaccination seems to protect or minimize these discomforts in the long term.” (I)
Source: Eluniverso
Paul is a talented author and journalist with a passion for entertainment and general news. He currently works as a writer at the 247 News Agency, where he has established herself as a respected voice in the industry.
