Cases of the actually rare monkeypox are being detected in more and more countries – in addition to Great Britain, Spain and Portugal now also in the north-east of the USA. The disease is usually mild, but the frequency of cases is so unusual that health authorities in the countries are calling for increased vigilance.

Many of those infected are men who have had sex with other men. The infections were probably transmitted through bodily fluids. While the monkeypox cases would not cause an epidemic like Covid-19, “it is a serious outbreak of a serious disease – we should take it seriously,” said Jimmy Whitworth, professor of international public health at the London School of Hygiene and Tropical Medicine to the Reuters news agency.

The US health authority CDC emphasizes that “any person, regardless of their sexual orientation, can spread monkeypox”. All age groups and all genders are equally susceptible – children and adolescents are particularly susceptible, as the Robert Koch Institute (RKI) writes. There is no specific medication or vaccination against monkeypox. One possible theory for the rise in case numbers is that population-wide immunization coverage against smallpox is declining around the world.

Human cases have been very rare outside of Africa, with most continuing to occur in areas of West and Central Africa. A mortality rate of around ten percent is given for the Central African virus variant. In the West African variant, almost all infected survive.

The first person affected in Great Britain also entered the country from Nigeria in West Africa at the beginning of May 2022. According to the UK Health Security Agency (UKHSA), the number of cases recorded in Great Britain is currently nine. Most are said to have been infected in London, although in some cases no direct link to those already infected could be established. Here, too, it is primarily men who have had sexual contact with other men who are ill.

In the United States, one person from the state of Massachusetts has been affected so far, the CDC said. In Spain, eight infections were reported in the capital Madrid. In Portugal, the newspaper “Público” wrote about 20 infected people, but this number has not been officially confirmed. Dozens of other suspected cases are being investigated, for example in Canada.

Anne Rimoin, a professor of epidemiology at the University of California, told Reuters that the new cases, while few, needed urgent investigation. This is important to find out whether monkeypox is a new way of spreading or whether the virus has changed.

Experts suspect that monkeys are just accidental hosts of the monkeypox virus. They can be infested, but the real reservoir is likely rodents like squirrels and rats. According to the RKI, infections can be transmitted to humans through contact with the blood or secretions of infected animals. Eating meat from infected animals and droplet infections are also other transmission routes. Transmission from person to person occurs through close contact, via droplets, pustular fluid and other body fluids or crusts.

According to the UKHSA, fever, headache, muscle and back pain, swollen lymph nodes, chills and exhaustion are among the first signs of illness. After one to four days, a rash may develop, often spreading to other parts of the body, starting from the face. The rash looks different depending on the phase and can resemble chickenpox and syphilis. Most sufferers recover within a few weeks. The World Health Organization (WHO) emphasizes that thorough hand washing with soap and water anyway helps to reduce the risk of transmission.

The smallpox vaccine can protect quite well against an infection with monkeypox or weaken the course of the disease. Smallpox has been considered eradicated worldwide since 1980 after a major vaccination campaign. Many people are not vaccinated at all and, according to the RKI, those who were vaccinated a long time ago no longer have any vaccination protection. According to WHO and CDC recommendations, active immune prophylaxis against monkeypox is currently not appropriate as a precautionary measure because of the possible side effects of smallpox vaccination.

In view of the first known cases in Great Britain, the RKI had already made doctors in Germany aware of the virus infection: monkeypox should also be considered as a possible cause in the case of unclear smallpox-like skin changes if those affected have not traveled to certain areas. Travelers returning from West Africa and men who have sex with men should “seek immediate medical attention” if they have any unusual skin changes.

The WHO also calls for rigorous tracking of all contacts of those affected. Clinics and the general public should have unusual skin rashes examined by specialist staff. If monkeypox is suspected, patients should be isolated. Health workers should take the usual precautions to protect themselves against infections that can spread through contact or droplets.

Monkeypox infections in humans have been increasingly diagnosed in Nigeria since 2017. According to the WHO, 558 suspected cases were reported there, 241 were confirmed and eight people died. There were other monkeypox outbreaks in 2018 in Congo, Cameroon and the Central African Republic.

In a 2019 article, RKI staff noted: “Outside of Africa, monkeypox has only been identified in humans three times: in 2003 in the USA and in 2018 in the United Kingdom and Israel”.

Lars Fischer, science editor at Spektrum, writes why more and more people are becoming infected with the virus. Population growth and more settlements near forests, as well as more interaction with potentially infected animals, may have favored the transmission of animal viruses to humans.