Brote de viruela del mono: ¿Cuál es la situación actual?

Monkeypox Outbreak: What Is the Current Situation?

21.6.2022
Monkeypox virion.jpg
Photo: National Institute of Allergy and Infectious Diseases (NIAID) - Colorized transmission electron micrograph of monkeypox virus particles (green) cultivated and purified from cell culture. Image captured at the NIAID Integrated Research Facility (IRF) in Fort Detrick, Maryland.

In the last two months, more than 1,300 cases of monkeypox have been reported in 28 countries (mostly in Europe) where the disease is not endemic (i.e. where cases are not usually reported because there is no animal reservoir of the virus). So many cases, in so many non-endemic countries and in such a short time is what has set off the alarm bells. It means that there is widespread transmission of the virus outside Africa and that it has probably been happening "under the radar" for months. However, it is important to note that the number of cases in the African region was already increasing markedly over the last four to five years, something that the international community showed little interest to investigate. So far this year alone, eight African countries have reported some 1,500 suspected cases and 72 deaths, according to the latest WHO report .

The number of cases in the African region was already increasing markedly over the last four to five years, something that the international community showed little interest to investigate

A WHO meeting is scheduled to take place on June 23, where, among other issues, the possibility of declaring a Public Health Emergency of International Concern (PHEIC) will be discussed. In the meantime, the current outbreak raises a number of questions: when and how did it start; has the virus changed or has our behaviour changed; can it be contained or is there a risk of it becoming endemic in countries that were not endemic?

Viral sequences from the current outbreak in Europe indicate that it is likely there was a single introduction, followed by a series of "super-spreading" events

What Do We Know So Far?

Viral sequences from the current outbreak in Europe indicate that the viruses are closely related, so it is likely there was a single introduction, followed by a series of "super-spreading" events. In fact, in the UK there appear to have been three introductions: one was an imported case from Nigeria that did not infect anyone. Another was in a family nucleus that did not spread further. And thirdly, a large cluster of cases in men who have sex with men.

There are about 50 mutations between the 2018 sequences and now, far more than would be expected for a DNA virus like monkeypox

Clues in the Genome

In all cases, the virus belongs to the least lethal clade and is closely related to the sequences of cases exported from Nigeria in 2018 and 2019. However, there are about 50 mutations between the 2018 sequences and now, far more than would be expected for a DNA virus like monkeypox, which mutates much more slowly than RNA viruses. According to virologists , it would take about 50 years to accumulate these mutations, not three or four. Moreover, the mutations do not appear to be randomly distributed. They are concentrated at specific sites that are targets for enzymes in the host (in this case, us) that are dedicated to introducing mutations into viruses in an attempt to disable them. Obviously, this is not a perfect defence system, and many mutations introduced by these enzymes fail to disable the virus. But they do leave a "mark" on its genome. And it is that mark that virologists believe they are seeing, suggesting continued spread in humans since 2017-2018.

What is not yet known is where it has been circulating - it may even have been circulating unnoticed outside Africa over the past two or three years

What is not yet known is where it has been circulating - it may even have been circulating unnoticed outside Africa over the past two or three years. It is also not yet known whether these mutations affect the virus’s behaviour. For example, whether they increase its ability to transmit from person to person, or whether they change the disease symptoms (the symptomatology observed in the current outbreak seems a little different). Since 2017, Nigeria has been asking the international community for help to investigate what was happening with the virus, but sadly - and predictably - we ignored it until the problem arrived on our doorstep.

Fortunately, unlike SARS-CoV2, we have more tools to deal with this emerging virus

What is being done?

Fortunately, unlike SARS-CoV2, we have more tools to deal with this emerging virus. The population above the age of 50 has been vaccinated against smallpox (which is very closely related) and would therefore be protected. Globally, there is a small stock of the classical smallpox vaccine, which could be used (although it is not clear how many exist in Europe). In addition, there is a more recently approved vaccine which, although its actual efficacy against monkeypox has not been tested, generates good immunity to the virus. We also have a couple of antiviral drugs that work against this family of viruses. The European Commission is in the process of negotiating the purchase of the antiviral drug tecovirimat and Bavarian Nordic’s Imvanex vaccine. Some countries are already starting to vaccinate close contacts of cases, but there is no reason to launch a mass vaccination campaign at this stage.

We do, however, need to do everything we can to curb human-to-human transmission (raising awareness in communities most at risk, isolating cases, and identifying and vaccinating contacts). Experts warn that the risk of not containing the current outbreak is that the virus could find a new animal reservoir outside Africa, resulting in multiple outbreaks in the future and increasing the risk of new variants emerging. It is also important to ensure that countries in Africa (where there are more cases) have access to diagnostic tests, treatment and vaccines.

Once again, a virus tests our solidarity, reminding us that a health problem somewhere far away affects us all.