The first cases were reported in Great Britain at the beginning of May 2022, and they are now piling up worldwide: more and more people are contracting monkeypox outside of Africa for the first time. In the meantime, several infections have also been confirmed in Germany.

Although the disease is generally much milder than an infection with the classic smallpox virus, scientists and health authorities are currently observing events closely. We explain what’s new about this outbreak, where the disease came from, how well a smallpox vaccination protects and whether the virus could also spread to local animals.

Monkeypox is a virus that can spread from animals to humans. Contrary to what their name might suggest, they are mainly found in rodents in West and Central Africa. So far, most people have been infected in these regions. Two virus variants are relevant for humans.

So far, all those who are currently ill have contracted the milder, West African variant.

Monkeypox becomes noticeable about five to 21 days after infection; most people develop symptoms after six to 13 days.

These include typical flu symptoms such as fever, headache, muscle and back pain and swollen lymph nodes. Only one to three days after the onset of the fever does a rash form on the skin and the smallpox that gives it its name: small nodules and fluid-filled blisters that crust over and fall off as the disease progresses. They often first appear on the face and then spread to the whole body, especially the palms of the hands and soles of the feet, the oral mucosa, the genital area and the eyes. However, those who are currently ill also report that the skin changes first appeared in the genital area.

Monkeypox infection is almost always mild; most sufferers recover within two to four weeks. However, that does not mean that the disease is harmless: it can sometimes be life-threatening, especially for younger children and people with a weakened immune system.

According to the Robert Koch Institute, up to eleven percent of children under the age of 16 who have been infected with the Central African virus variant have died from monkeypox in the past. However, the data available so far is poor. The World Health Organization (WHO) currently assumes that three to six percent of all those infected will die.

So far, cases of monkeypox have been known almost exclusively from Africa. Infections in humans have been regularly observed here for decades, even if they are relatively rare. According to the WHO, only isolated infections in humans could be detected outside of the continent before 2022, for example in Great Britain, the USA, Israel and Singapore. Those affected had been infected while traveling to Nigeria or Ghana or had come into contact with contaminated materials that travelers had brought with them on their return. In 2003, around 70 people in the United States became infected from prairie dogs kept with rodents from Ghana. Human-to-human transmissions were probably not observed.

What is new, however, is that infections occur that can no longer be directly traced back to West or Central Africa. The high number of reported cases and their widespread distribution is also unusual. Well over 100 infections have now been detected worldwide, including in Germany, Great Britain, Belgium, Sweden, Portugal, Spain, Italy, the USA and Canada. Since the incubation period of the disease is up to three weeks, experts assume that more cases will be discovered in the near future.

In principle, changes in the viral genome could have made monkeypox more contagious. However, the virus evolves comparatively slowly. Its genome consists of DNA and is therefore more stable than that of the rapidly changing RNA viruses such as the influenza virus or Sars-CoV-2.

The results of the first available gene analyzes cannot yet be interpreted with certainty. In order to explain the current outbreak, it is also not absolutely necessary that the virus is more contagious. It is also possible that a combination of different circumstances – for example particularly favorable conditions for the spread or a superspreader event – is behind the high number of infected people.

The most important long-term consequences are skin changes and scars left by the pustules typical of monkeypox. These can be local pigment disorders, but also bowl-shaped, deepened skin scars. The eyes are also affected in some of the infections – in a review study in a quarter -.

The virus causes a type of conjunctivitis, or corneal inflammation, which in some cases can cause scarring of the cornea, permanently reducing vision. In addition, experts report other serious complications, such as bacterial infections, sepsis, neurological problems and pneumonia, which in turn can cause permanent damage.

Experts assume that the smallpox vaccination, which was compulsory for children in Germany until the 1980s, is also effective against monkeypox. However, the classic smallpox vaccine that was used back then is no longer approved in this country due to its side effects.

However, there is now a new, modified vaccine that, according to data from Africa, protects against infection with monkeypox in about 85 percent of cases; whoever becomes infected nevertheless becomes ill more mildly. In principle, people who have already had contact with a sick person can still be vaccinated. If the vaccine is given within four days of infection, an outbreak of the disease can often still be prevented.

Like previous vaccines, the smallpox vaccine, which is now approved for adults in the EU, is based on a modified vaccinia virus, which also belongs to the poxviruses and is similar to the human and monkeypox virus. Compared to human smallpox, however, it hardly causes any symptoms. It can be found in a weakened form in the live vaccine, which can no longer reproduce in the human body.

So far there has been no recommendation for people in Germany to be vaccinated against monkeypox. Since, according to the current state of knowledge, close contact is necessary for transmission, the chances are high that the outbreak will also fizzle out. According to the WHO, the longest chains of infection that have been documented so far were around six to nine people long.

However, one is considering a vaccination recommendation for people who are particularly at risk, said Federal Health Minister Karl Lauterbach on May 23 on the sidelines of the World Health Assembly in Geneva. In Great Britain, the British health authority is now advising contact persons with a high risk of infection to be vaccinated with the smallpox vaccine. These include household members or sexual partners of infected people.

The first regulations for dealing with sick people are in the works:

On May 24, Federal Minister of Health Karl Lauterbach announced that an ordered isolation of at least 21 days should be recommended for infected people and their contact persons. The recommendation was developed together with the Robert Koch Institute (RKI), said Lauterbach at a press conference during the German Doctors’ Day.

Monkeypox is actually an animal disease, presumably in rodents, that only occasionally spreads to monkeys and humans. In addition, a whole range of different animal species have been shown to be susceptible – even outside of Africa. Theoretically, it is therefore possible for animals to become infected with infected people and pass the virus on to each other. Such an animal reservoir would be a major problem in combating monkeypox, because the virus can spread back to humans from there at any time. This is also the case in Nigeria, for example, which has a handful of cases every year – more than 500 as of 2017.

Such a situation is conceivable in Europe, but unlikely: “Although the range of monkeypox hosts for a spill-over infection is broad, whether there are also animal species in Europe that can be considered suitable reservoir hosts and can spread the virus further, is rather questionable,” says Martin Beer, head of the institute for virus diagnostics at the Friedrich-Loeffler-Institute in Greifswald. First of all, you need such a susceptible animal species, which then has sufficiently close contact with an infected person and must be able to to efficiently infect other animals, explains the virologist.

Although a single pet such as a cat could be infected through direct contact with an affected person, the virus would first have to be passed on to other individuals in a population. “It is therefore very unlikely that the virus will establish itself in a new animal population in Europe,” says Beer.

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