Four new human cases of monkeypox have been identified in the UK. This increases the number of known infected people to seven. Evidence to date suggests there is previously unknown community transmission, reports the UK Health Security Agency (UKHSA), the agency responsible for public health and infectious diseases. Outside of Africa, this has never happened before. Monkeypox is believed to have originated in rodents in Central and West Africa and has repeatedly spread to humans. Cases outside of Africa are rare and have so far been attributed to infected travelers or imported animals.

On 7 May 2022, it was revealed that a person who had entered the UK from Nigeria had contracted monkeypox, and a week later authorities reported two more unrelated cases in London. The four patients who have now been identified also had no known contact with the three previous cases. This speaks for previously unknown chains of infection in the population.

According to the World Health Organization, everyone in the UK has contracted the West African variant of the virus, which is mild and clears without treatment in most people. The infection begins with fever, headache, body aches and exhaustion, after one to four days a rash develops and the blisters and pustules typical of smallpox, which crust over.

All four of the new infected are homosexual or bisexual men and were infected in London, UKHSA reports. The experts suspect that the transmission takes place in this community. The virus spreads during the fever phase through droplets and, according to the Robert Koch Institute, presumably also through aerosols, later through the pustular fluid and scab crusts and objects that have come into contact with them. However, according to most professionals, close contact is required for contagion.

The cluster of cases is “rare and unusual,” says Susan Hopkins, senior medical adviser to the UKHSA. The authority is currently tracking the contacts of the infected. While data from the Democratic Republic of the Congo suggest an effective reproductive number of 0.3 to 0.6, there is growing evidence that the virus can be sustained among humans under certain conditions. For reasons that are not yet clear, the number of infections and outbreaks is increasing significantly, which is why monkeypox is considered a potential global threat.

It is unclear what proportion of those infected die from monkeypox due to the poor data situation. Known risk groups are people with immunodeficiency and children, in pregnant women an infection can lead to miscarriages. For the Congo Basin variant of the virus, some sources indicate mortality rates of ten percent and more, more recent surveys show case mortality rates of up to five percent. In contrast, almost all infected survive in the West African variant. In the largest outbreak, in Nigeria in 2017, six people died, four of them with weakened immune systems.

There are currently no specific medications for monkeypox. You treat the symptoms of the disease and prevent, for example, additional bacterial infections that can cause problems with such viral diseases. Very early in the disease, the course can be attenuated by giving the smallpox vaccine or an antibody preparation obtained from vaccinated people. There is also a live vaccine, which is only available in the USA for targeted vaccinations in future outbreaks. It is not approved in Germany.

The number of cases in the UK and evidence of ongoing transmission between people outside of Africa is the latest evidence the virus is changing behaviour. Analysis shows that the number of cases in the Democratic Republic of the Congo may have increased twenty-fold between 1980 and 2007. Additionally, the virus has resurfaced in several West African countries after decades; since 2017, for example, there have been more than 500 confirmed cases and eight deaths in Nigeria.

It is not yet known why so many more people are contracting the virus. The factors that also favored the Ebola epidemics in West Africa and in the Democratic Republic of the Congo, each with several thousand infected people, may play a role. Experts suspect that factors such as population growth and more settlements near forests, as well as more interaction with potentially infected animals, favor the transmission of animal viruses to humans. At the same time, viruses spread faster due to higher population densities, better infrastructure and more mobility.

The spread in West Africa could also indicate that the virus has spread to a new animal reservoir. A whole range of animals can be infected with the virus – in addition to many rodents, there are also monkeys, pigs and anteaters. Infected animals transmit the virus to other species and to humans with relative ease – as happened in the first outbreak outside of Africa. In 2003, the virus entered the United States with African rodents; these in turn infected prairie dogs, which were sold as pets. At least 47 people became infected with monkeypox.

Perhaps the most important factor, however, is that population-wide immunization coverage against smallpox is declining around the world. The smallpox vaccine reduces the likelihood of contracting monkeypox by around 85 percent. However, since the end of the vaccination campaign, the proportion of those who have not been vaccinated has risen steadily, making it easier for monkeypox to spread among humans. The proportion of human-to-human transmissions in all infections has risen from around one third in the 1980s to three quarters in 2007. The fact that the average age of those infected increases the longer the vaccination campaign has passed also speaks for an influence of the vaccinations.

In view of these trends, African experts in particular warn that monkeypox could develop from a regional zoonosis to a globally relevant infectious disease. The virus could potentially occupy the ecological and immunological niche that smallpox once occupied, a team led by Malachy Ifeanyi Okeke from the American University of Nigeria wrote in a 2020 publication.

“There is currently no global system to control the spread of monkeypox,” Nigerian virologist Oyewale Tomori said in an interview with The Conversation magazine. However, it is highly unlikely that the outbreak will become an epidemic in the UK The risk to the public has been low so far, the UKHSA said, but the agency is now looking for additional cases and working with international partners to see if there are similar clusters of monkeypox internationally.

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