Why viruses (and coronaviruses) are so difficult to treat compared to bacteria

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Sergi Maicas Prieto, Universitat de València

Cough, runny nose, fever, muscle pain? We visit a medical service to obtain a reliable diagnosis and, if possible, an effective and quick remedy. If the origin is bacterial, we have had “some luck”. A few doses of antibiotics usually return us to a normal state in a few days or weeks. On the contrary, when the origin is viral the situation is complicated. We do not have an antiviral arsenal at the same level, neither in quantity nor in effectiveness. The immune system is, on many occasions, our only ally.

Bacterial infections

Although they are usually confused, both groups of microorganisms are radically different and we should not put them in the same bag. Bacteria are single-celled living organisms that do not have a defined nucleus (prokaryotes), unlike human cells (nuclei, eukaryotes).

When bacteria live with us, they are part of what we know as a microbiota. There are tens of thousands of species that are part of this concept, in such a way that we can consider it as one more organ of our body. Its genes (microbiome) provide almost fifty times more genetic information than what we have in strictly human cells in our bodies. Coexistence is usually peaceful, and both our nucleated cells and our bacteria coexist.

We know our bacteria quite well; we can control their pathogenic mechanisms and fight the diseases they cause. The treatment for bacterial diseases, if you have a suitable antibiotic, can be relatively affordable. Except for some serious infections causing pneumonia or tuberculosis, or those caused by multidrug-resistant bacteria, adequate antibiotic therapy counteracts bacterial action.

Viral infections

Viruses are something else. These are infectious agents that inexorably need to parasitize a living cell that provides them with shelter, in order to survive and reproduce. As with human travelers, each virus chooses a type of accommodation, which it selects more or less specifically.

When a virion (that is, a virus in the extracellular phase) possesses the key to the lock that allows access to the cell, the door opens and viral infection is triggered. Once they invade human cells, they take control of their machinery for their own benefit, at the cost of total or partial destruction of the host itself. And for this, they use multiple strategies, which are also much more variable than those of cells.

The bad thing is that antibiotics don’t even tickle them. When used improperly – that is, to treat a viral infection – the effect they have on our bodies is to weaken our bacterial allies. Except for those exceptions in which viruses and bacteria attack us in a coordinated way, using antibiotics in the face of a viral disease negatively affects our health.

Do we already have antiviral treatments?

If there is no previous pathology or our immune system is weakened by another cause, the consequences of a viriasis can be slight, as it happens with the common cold). Our body simply reacts and solves the problem autonomously. It only represents a week of weakness that is usually alleviated with symptomatic treatments (pain relievers).

To fight against more aggressive viruses, with more serious associated pathologies, we have some antiviral drugs. Especially after the baggage that AIDS has brought us, which increased the number and variability of available antivirals. Each can be applied only to specific types of viruses because the mechanisms of action of each virus are different.

The objective of an antiviral is basically to inhibit the replication of the virus. Each drug attempts this at a different stage, blocking either virus adhesion to the cell, penetration, copying of its nucleic acid, synthesis of new proteins, or maturation/release of new infectious particles. All strategies are intended only to give our immune system time to catch up and fight disease from within.

Antivirals or vaccines against coronavirus?

AIDS can be treated with the administration of antiretroviral compounds, attacking a specific protein that allows the virus to replicate. However, against other respiratory viruses such as the coronavirus or the flu this strategy is not possible. Right now to combat the coronavirus, effective antivirals are being compassionately administered against other viruses such as Ebola, Marburg or MERS.

With compassionate, we mean that its use is authorized for an indication not contemplated in its technical data sheet, without absolute certainty that it will serve. We refer to compounds like REMDESIVIR, OSELTAMIVIR or RITONAVIR, which are being tested in hospitals to treat the pandemic. Even malaria treatments like CHLOROQUINE seem to have some positive effect.

If the current forecasts are confirmed in a few months we will have vaccines against this coronavirus. And yes, in general against viruses we should make use of each and every one of the vaccines available. There is only one inconvenience, as viruses mutate constantly and inexorably, having 100 percent effective vaccines is impossible.

If we are already immunized by previous exposure or have a vaccine (such as the flu), we are faced with a known scenario. In the face of the pandemic caused by a new virus-like SARS-CoV-2, however, we have a more unpredictable one. Reaction capacity is less, and until vaccines are available or much of the population has been immunized by exposure, the effects are unknown.

At this point, I have some doubts. If in a few months, or maybe years, we have a vaccine against the new coronavirus, will we get it? Will anti-vaccine movements also arise against the coronavirus? The questions remain in the air.

Sergi Maicas Prieto, Associate Professor. Department of Microbiology and Ecology. Master’s Degree in Molecular, Cellular and Genetics Biology, Universitat de València

This article was originally published in The Conversation. Read the original.

The Conversation