European and American health officials have identified several cases of monkeypox recently, mostly in young men. The cases reported in Europe and the United States are raising concern because the disease has rarely appeared outside of Africa. International health officials say the risk to the general population is low. They are keeping watch for cases because, for the first time, the disease appears to be spreading among people who did not travel to Africa. Monkeypox is a virus from monkeys that was first identified in 1958. It spreads among wild animals and sometimes jumps to people. Most human cases have been in central and west Africa, where the disease is endemic. The first known human infection was in 1970, in a 9-year-old boy in a distant part of Congo. Monkeypox belongs to the same virus family as smallpox but causes milder symptoms. Most patients only experience fever, body aches, chills and tiredness. People more seriously sick may develop a rash and cuts on their face and hands that can spread to other parts of the body. The virus develops in a human body from about five days to three weeks after infection. Most people recover within about two to four weeks without needing to be hospitalized. Monkeypox can result in death for up to one in 10 people and is thought to be more severe in children. People exposed to the virus are often given one of several smallpox vaccines, which have been shown to be effective against monkeypox. Anti-viral drugs are also being developed. On Thursday, the European Center for Disease Prevention and Control said all suspected cases should be isolated and that high-risk contacts should be offered the smallpox vaccine.