Viruses that are ‘hidden’ in the body and can cause problems after decades

If viruses could be defined by a single characteristic, objectivity would be a good option. After all, its goal 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 for a few days, and the immune system is able to deal with the problem or the condition evolves into a more serious, life-threatening situation.

But there is a group of viruses that go one step further. Soon 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 it only ends when the defense cells stop working as expected. Then the infection reappears and causes health problems again.

And this group has several well-known representatives, ranging from HIV, the cause of AIDS, to herpes simplex 1 and 2, which cause sores in 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 with Sars-CoV-2, the coronavirus responsible for Covid-19?

An appendix (or an edition) in the book of life

Basically, there are four ways a virus can hide in the body.

The first of these is frequently used by the herpes family, which in addition to the herpes simplex virus types 1 and 2, includes chickenpox, which causes chickenpox, Epstein-Barr, which is behind the “kissing disease”, among others.

“They have DNA as their genetic material and manage to stay inside the nucleus of the cells, as an appendix of our own genetic code”, explains infectious disease specialist Décio Diament, from 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” on two strands, usually in the classic double helix format.

“These viruses of the herpes family stay dormant for a long time, without replicating very intensely. 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 for the SBI (Society Brazilian Institute of Infectious Diseases).

The second mechanism 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, their genetic information is organized in a simpler way, in a single strand of sequences of nitrogenous bases.

Retroviruses are able to fuse with our genetic code. This integration happens most often in T lymphocytes and macrophages, two important parts of the immune system.

But how do they achieve 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. In short, it can convert the genetic code of these viruses from RNA to DNA. With this, they are able to embed themselves in the human genome and remain hidden for a long time.

“This represents an enormous difficulty, because we can’t eliminate them even with the available drugs”, says doctor 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. of January.

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.

Shrines and Other Mysteries

The third hiding option for some viruses is the so-called immunoprivileged sites.

These are regions of the body that the immune system cannot access so easily, such as the testes, eyes and central nervous system (spinal cord and brain).

The action of defense cells is limited in these places to prevent the inflammatory process, which occurs when they are fighting an infection, from damaging more sensitive structures, such as the nerves and the reproductive system.

If, on the one hand, this represents a form of protection for the body itself, on the other hand, it 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 the semen of patients, for example.

Immunologist Daniel Mucida, a professor at Rockefeller University in the United States, considers that the fact that the virus is found in semen or in other parts of the body does not necessarily mean that it is active and can cause future problems.” The impact of this persistence viral is still unclear,” 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 is eventually able to eliminate the invaders.

There is still a fourth group of viruses capable of prolonging their stay in the body, even outside of immuno-privileged sites.

“This is the case of the respiratory syncytial virus, which can persist in the lungs and is associated with chronic inflammation, especially in children, and the chikungunya virus, which remains in the muscles and joints”, exemplifies immunologist Carolina Lucas, a researcher at the School of Medicine. from Yale University in the United States.

Scientists are still studying why this happens in some patients (and not in others).

immune stumble

While it may seem like all 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,” says Diament.

This “silly” varies from infection to infection. In the case of herpes simplex, if the infected individual spends long hours in the sun or is in a very stressful time of life, this may be enough for the lesions to sprout again.

In other situations, the body’s own natural aging makes room for some infectious agents to resume work.

The classic example of this is varicella-zoster, a virus that causes chickenpox (usually in childhood) and then spends decades hidden in the body.

Later, after the age of 50 or 60, this pathogen can reappear and cause a condition called herpes zoster or shingles, marked by lesions in the form of very painful blisters on a strip of the body, usually on the trunk or abdomen.

Nowadays, there is even a vaccine indicated for these older individuals. In Brazil, it is only available on the private network.

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 accidents and severe trauma, major surgery, transplants, tumors, drug treatments and other serious infections,” says Diament.

In these cases, doctors already keep an eye on them and can provide treatments to minimize the damage.

Finally, it is also worth remembering that some pathogens are related to diseases that do not always have to do with the initial manifestations of the infection.

This is the case with some hepatitis viruses, which can cause liver cancer, HPV, which is behind several types of tumors, and Epstein-Barr, which has recently been linked to multiple sclerosis.

And the coronavirus?

Faced with such a great diversity of viruses, could Sars-CoV-2, the cause of Covid-19, also persist after the initial infection?

The experts consulted by BBC News Brasil consider it unlikely that he has or develops this capacity.

“Sars-CoV-2 is an RNA virus that does not have that reverse transcriptase enzyme, like HIV. Therefore, it cannot integrate into our genome”, says molecular biologist Carlos Menck, from the Institute’s Department of Microbiology. of Biomedical Sciences at the University of São Paulo (ICB-USP).

It also does not have DNA in its constitution, as with viruses of the herpes family, which prevents its prolonged persistence in the cell.

“And the cases that we see now, of people who have Covid again, happen because they became infected with the coronavirus for the second time, and not because it was hidden in their body for months”, explains the specialist.

“If we see anything different from that with Sars-CoV-2, it will be a very big surprise for us.”

But how to explain the cases of long Covid, in which individuals present discomfort for months, even after recovering from the first discomfort?

Diament clarifies that this phenomenon seems to be more related to the immune system’s response to the invasion of the coronavirus.

“In some patients, Covid causes real damage that can last for months and manifest itself through fatigue, difficulty concentrating, loss of smell…”

“This seems to be a consequence of the inflammatory process that occurs during the first days of infection. In some cases, the immune system reacts violently, and the effects of this can be prolonged”, says the doctor.

Luca and Mucida say, however, that in these cases the persistence of some viral components, such as pieces of protein and RNA, in the organism is ruled out.

“There is evidence that points to both sides, including the observation of viral RNA in regions such as the intestine in a prolonged way”, they say.

It remains to be seen whether these little pieces of virus would be able to keep the immune system in a wakeful state and cause damage for weeks or months or are just a finding with no practical effect on people’s health.

But, as Portela Nunes points out, in the case of Covid-19, we already have at least one good news: “Vaccination seems to protect or minimize these long-term annoyances”.

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