It's not clear how some people recently diagnosed with the disease contracted monkeypox virus, or how it spread More new human monkeypox cases have been detected worldwide, with dozens of reports in the UK alone.According to the UK Health Security Agency (UKHSA), there was previous evidence of unknown spread of monkeypox virus in the country's population.Monkeypox is thought to have originated in rodents in Central and West Africa and has been transmitted to humans multiple times.Cases outside Africa are rare and have so far been traced to infected travelers or imported animals. On May 7, it was reported that a person travelling from Nigeria to the UK had contracted monkeypox.A week later, authorities reported two other cases in London that were apparently unrelated to the first.At least four of those recently identified as having the disease had no known contact with the three previous cases -- suggesting an unknown chain of infection in the population. According to the World Health Organization, all infected people in the UK have contracted the West African branch of the virus, which tends to be mild and usually resolves without treatment.The infection starts with fever, headache, sore extremities and fatigue.Usually, after one to three days, a rash develops, along with blisters and pustules similar to those caused by smallpox, which eventually crust over. "It's an evolving story," said Anne Limoyne, a professor of epidemiology at the UCLA Fielding School of Public Health.Rimoin, who has been studying monkeypox for years in the Democratic Republic of Congo, has many questions: At what stage of the disease process are people infected?Are these really new cases or old cases just discovered?How many of these are primary cases - infections traced to animal contact?How many of these are secondary cases or person-to-person cases?What is the travel history of the infected person?Is there a connection between these cases?"I think it's too early to make any definitive statement," Rimoin said. According to UKHSA, many of the infected people in the UK are men who had sex with men and contracted the disease in London.Some experts believe transmission may be occurring in the community, but also through close contact with other people, including family members or health care workers.The virus is spread through droplets in the nose or mouth.It can also be spread through bodily fluids, such as pustules, and objects that come in contact with it.However, most experts say close contact is necessary for infection. Susan Hopkins, UKHSA's chief medical adviser, said this cluster of cases in the UK was rare and unusual.The agency is currently tracing contacts of infected people.Although data from the Democratic Republic of Congo in the early 1980s and mid-2010s indicated that the effective reproduction numbers at that time were 0.3 and 0.6 respectively - meaning that each infected person transmitted the virus to less than one person in these groups on average - the more There is growing evidence that, under certain conditions, it can spread continuously from person to person.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. Experts did not immediately express concern about a widespread international outbreak as the situation was still evolving."I'm not that worried" about the possibility of a larger epidemic in Europe or North America, said Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.Historically, the virus has mostly been transmitted from animals to people, and human-to-human transmission usually requires close or intimate contact."It's not as contagious as COVID, for example, or even as contagious as smallpox," Hotez said. The bigger problem, he said, was the spread of the virus from animals -- possibly rodents -- in the Democratic Republic of Congo, Nigeria and West Africa."If you look at some of our toughest infectious disease threats -- whether it's Ebola or Nipah or coronaviruses like the ones that cause SARS and COVID-19 and now monkeypox -- these are disproportionate Zoonoses, which spread from animals to humans," added Hotez. The proportion of infected people who die from monkeypox is unknown due to insufficient data.Known risk groups are the immunocompromised and children, where infection during pregnancy can lead to miscarriage.For the Congo Basin branch of the virus, some sources indicate a fatality rate of 10% or higher, although recent investigations suggest a case fatality rate of less than 5%.By contrast, nearly everyone infected with the West African version survived.During the largest known outbreak that began in Nigeria in 2017, seven people died, at least four of whom had weakened immune systems. There is no cure for monkeypox itself, but the antiviral drugs cidofovir, brindofovir and tecovir mate are available.(The latter two are approved in the U.S. to treat smallpox.) Health care workers treat symptoms and try to prevent additional bacterial infections that sometimes cause problems during such viral illnesses.Early in the monkeypox disease course, the disease can be alleviated by vaccination with monkeypox and smallpox or with antibody preparations obtained from vaccinated individuals.The U.S. recently ordered millions of doses of the vaccine to be produced in 2023 and 2024. The number of cases in the UK, and evidence of continued transmission among people outside Africa, provides the latest sign that the virus is changing its behaviour.A study by Rimoin and colleagues suggests that the rate of cases in the Democratic Republic of Congo may have increased 20-fold between the 1980s and the mid-2000s.A few years later, the virus re-emerged in several West African countries: in Nigeria, for example, there have been more than 550 suspected cases since 2017, of which more than 240 have been confirmed, including 8 deaths. Why more Africans are now contracting the virus remains a mystery.Factors that led to the recent Ebola outbreak, which infected thousands in West Africa and the Democratic Republic of Congo, may have played a role.Experts believe factors such as population growth and more settlements near forests, as well as increased interaction with potentially infected animals, favor the spread of animal viruses to humans.At the same time, due to higher population densities, better infrastructure and more travel, the virus typically spreads faster, potentially leading to international outbreaks. The spread of monkeypox in West Africa may also indicate that the virus has emerged in a new animal host.The virus can infect a variety of animals, including several rodents, monkeys, pigs, and anteaters.Infected animals are relatively easy to spread it to other types of animals and humans -- and that's what's been the first outbreak outside of Africa.In 2003, the virus entered the United States through African rodents, which in turn infected prairie dogs sold as pets.During that outbreak, dozens of people in the country were infected with monkeypox. However, in the current spate of monkeypox cases, the factor believed to be the most important is the declining population-wide vaccination coverage against smallpox worldwide.Vaccination against smallpox reduces the chance of contracting monkeypox by about 85%.However, the proportion of unvaccinated people has risen steadily since the end of the smallpox vaccination campaign, making monkeypox more susceptible to infecting humans.As a result, the proportion of human-to-human transmission of all infections has risen from about one-third in the 1980s to three-quarters in 2007.Another factor contributing to the decline in vaccination is that the average age of people infected with monkeypox has increased with the number.Time since the end of the smallpox vaccination campaign. African experts have warned that monkeypox could transform from a regionally endemic zoonotic disease to a globally relevant infectious disease.The virus may be filling an ecological and immune niche once occupied by smallpox, Malachy Ifeanyi Okeke of the American University of Nigeria and colleagues wrote in a 2020 paper. "Currently, there is no global system to manage the spread of monkeypox," Nigerian virologist Oyewale Tomori said in an interview published in The Conversation last year.But according to UKHSA, it is highly unlikely that the current outbreak will become an epidemic in the UK.The risk to the British public has so far been low.Now, the agency is looking for more cases and working with international partners to find out if similar monkeypox clusters exist in other countries. "Once we've identified cases, then we're going to have to do a really thorough case investigation and contact tracing -- and then some sequencing to really combat how this virus is spreading," Rimoin said.The virus may have been circulating for some time before public health authorities noticed."If you flash a flashlight in the dark," she said, "you'll see something." Rimoin added that until scientists understand how viruses spread, "we have to continue with what we already know, but with humility -- remember that these viruses can always change and evolve."