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Monkeypox: transmission, lethality… Latest scientific advances

The first hypotheses appear. Although cases of monkeypox have increased in recent days, scientists are beginning to better understand how the virus was able to spread so quickly around the world and especially in Europe. This pathogen, endemic to West and Central Africa, has so far only caused rare infections outside these regions. But since the first patient was found in the United Kingdom on May 7, 68 cases have been confirmed in the Old Continent, including three in France, and 42 others are under investigation, according to a report from the European Center for Disease Prevention and Control. (ECDC) published May 23. Patients have also been treated in Canada, USA, Australia, Israel and Switzerland.

A common feature was found between the majority of patients: they are men, young, declaring sexual relations with other men. These characteristics quickly led epidemiologists to the trail of several crowded places that could serve as foci of the epidemic. In their field of vision is a festive event that took place in the Canary Islands from May 5 to 15. Approximately 80,000 people from all over the continent gathered here for the “Gran Canaria Pride Festival”. “This could have contributed to the progressive spread of the virus from an infected person who would have participated in this party,” notes Antoine Jessen, head of the epidemiology and physiopathology of oncogenic viruses at the Pasteur Institute, who has been working on the disease for several years. According to the Spanish authorities, another source of infection should have appeared in the Madrid “sauna”, which was appreciated by the gay community. However, these are only the first clues, because if several patients have visited these places, then not all of them. Therefore, investigations are still ongoing.

Infectious patients before the appearance of pustules

Although the virus currently circulates primarily among homosexuals, health authorities insist that monkeypox is not a sexually transmitted disease. “Anyone can get infected, all it takes is close contact,” a World Health Organization official told a conference on Monday, May 23. Transmission occurs through contact with pus from skin lesions formed during infection, as well as through other body fluids, including droplets of saliva, when coughing, sneezing. However, this virus remains far less contagious than chickenpox or Sars-CoV-2, the cause of the Covid pandemic. “However, patients can become infected in the prodromal phase, that is, when they have fever and headaches, but do not yet have a characteristic rash,” notes Antoine Jessen.

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Despite the sudden appearance of this pathology in a number of developed countries, scientists do not yet show much concern. Although the name of the disease may be intimidating – smallpox killed millions of people around the world before it was eradicated – in fact, monkeypox has little to do with “smallpox” and its 30% mortality rate. The symptoms are much less severe: “Two monkeypox viruses circulate in Africa, one with a fatality rate of 3% to 10% and the other 1%. This is the one currently found in Europe,” says Antoine Jessen. If this figure seems higher than Covid, this expert wants to be very encouraging: “This is the mortality seen in African countries where the population has comorbidities, even malnutrition and, above all, limited access to medical care.” The main factors, he says: deaths, especially in children, are indeed associated with pre-existing fragility in combination with the appearance of bacterial superinfection of pustules. This can lead to sepsis if not properly treated. In Western countries, this pathology has never led to a fatal outcome so far. In the United States, 47 people, including children, became ill in 2003 after infected prairie dog animals were brought into the country. No one succumbed to this infection, and the epidemic quickly died out.

“Reactive” vaccination in case of contact with the diseased

The disease can sometimes leave scars, but according to Antoine Jessen, they are less important than with chickenpox. Moreover, unlike Sars-CoV-2, this virus is nothing new. It has been known for several decades and has been well studied. Thus, the risk to the general population appears to be very low. However, ECDC urged European countries to be vigilant and strengthen their monitoring systems. This is done in part to protect those who are most at risk of developing serious forms, such as pregnant women or immunocompromised patients. Thus, various governments are invited to test their testing and sequencing capabilities, as well as their stockpiles of protective equipment, vaccines and treatments. The smallpox vaccine is indeed effective against monkeypox, against which it provides 85% protection, and can be used before and after exposure, up to four days after a dangerous exposure.

However, there may be questions about the availability and use of this product. The General Directorate of Health confirms that France does indeed have a stockpile of smallpox vaccines, the quantities of which are “classified”. However, ECDC notes that no vaccine specifically for monkeypox is allowed in Europe. According to the High Office of Health, the oldest smallpox vaccines have serious side effects and “should not be used”. Another smallpox injection was developed more recently from an inactivated virus and allowed in Europe. This product has also been tested in animals against monkeypox where it has shown very good efficacy. On the other hand, “human efficacy data are lacking, as are safety data in immunocompromised people,” the ECDC points out. Therefore, the European Organization decides against preventive vaccination in homosexual communities at this stage, both because of “limited supplies and because of the unfavorable balance of benefits and risks.” However, in France, HAS has advocated reactive vaccination after exposure to a case to curb the spread of the virus, in other words, all “adults whose contact with an infected person is considered at risk, including those who have been exposed”. medical workers without personal protective equipment. An antiviral treatment, tecovirimat, is also allowed in Europe, but similarly, the number of available doses remains limited under the ECDC. Next week WHO is organizing an international meeting on this issue.

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Thus, at this stage, containment of the spread of the disease by tracing and isolating cases and their contacts remains the best prevention. Which should be easier than for Covid, because there is no asymptomatic transmission of this virus. “We will undoubtedly see an increase in the number of patients in the coming days and weeks. But if such surveillance is effective, the epidemic should quickly die out on its own,” says Antoine Jessen. Unless the virus manages to catch up with us and find an animal reservoir in Europe where it could become endemic. But the likelihood of such a development of events, which ECDC mentions, seems to European experts “very low.”

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