The World Health Organization on Saturday declared the outbreak, which has affected nearly 16,000 people in 72 countries, a global health emergency — the highest alarm it can sound.
Monkeypox, so named because it was first discovered in a monkey, is related to the deadly smallpox virus, which was eradicated in 1980, but is much less serious.
The species currently circulating outside of Africa is the milder of two known versions. Human monkeypox was first diagnosed in 1970 in Zaire (now the Democratic Republic of the Congo) in a nine-year-old boy.
It is becoming endemic to the tropical rainforests of Central and West Africa, where 11 countries report cases.
The virus is transmitted through close contact with infected animals, usually rodents, or humans.
In June 2003, the disease surfaced in the United States — the first time it was discovered outside of Africa.
The disease is believed to have spread after rodents imported to the US from Ghana infect prairie dogs.
The US Centers for Disease Control and Prevention (CDC) report 87 cases, but no fatalities.
2017 brings a major outbreak in Nigeria, with more than 200 confirmed cases and a death rate of about three percent, according to the WHO.
Over the next five years, sporadic cases will be reported in travelers arriving from Nigeria around the world, particularly in Britain, Israel, Singapore and the United States.
In May 2022, a spate of cases will be discovered in countries outside Africa, in people without travel connections to the region. Most of those affected are gay men.
Europe is the epicenter of the new outbreak.
On May 20, Britain registered 20 cases, mostly among gay men.
On the same date, the WHO counted 80 confirmed cases worldwide, including in Australia, Belgium, Canada, France, Germany, Italy, Portugal, Spain and Sweden.
On May 23, the United States says it is preparing to administer smallpox vaccines, which are effective against monkeypox, to people who have been in close contact with monkeypox patients.
Three days later, the European Union says it is in the process of centralizing vaccine purchases, just as it was for Covid-19.
In early June, WHO chief Tedros Adhanom Ghebreyesus said more than 1,000 confirmed cases of monkeypox had been reported to WHO from 29 countries where the virus is usually absent.
On June 21, Britain will announce plans to offer vaccines to gay and bisexual men with multiple sexual partners.
WHO experts will meet on June 23 to discuss the threat but decide monkeypox is not a global public health emergency.
On July 8, health authorities in France are also launching preventive injections for people considered to be at risk, including gay men, transgender people and sex workers.
On July 14, the US CDC reports more than 11,000 confirmed cases in some 60 countries where monkeypox is not commonly found. Most cases are in Europe, the United States and Canada.
The number of infections in New York doubles to several hundred in less than a week. People are queuing for vaccines, which are in short supply.
On July 20, Tedros announced that nearly 14,000 confirmed cases have been reported to the WHO this year, from more than 70 countries, with five deaths, all in Africa.
He says six countries reported their first cases in the past week, while some states have limited access to diagnostics and vaccines, making the outbreak harder to track and stop.
The WHO will convene a new meeting of experts on July 21 to decide whether to declare a global health emergency.
On Saturday, Tedros announced that the monkeypox outbreak is a “public health emergency of international concern”.
Watch WHO declares monkeypox a global health emergency as infections rise