While the total number of monkeypox cases worldwide stands in the hundreds, scientists have said the disease may have been spreading undetected for weeks, months or years before the first cases outside of Africa are reported in this year’s outbreak.
Today, 780 confirmed cases of monkeypox have been reported since the outbreak began on May 13 this year (until June 2), with at least 27 World Health Organization (WHO) member states reporting cases, including the United States and Canada.
Investigations are underway to find out more about why monkeypox is spreading to countries where it does not normally occur – the disease is endemic in African countries such as the Democratic Republic of Congo, Cameroon and the Republic Central African Republic, where thousands of cases are reported every year.
However, in an update on the outbreak published last week, the WHO said the “sudden and unexpected” spread of monkeypox in several non-endemic countries suggested that “there may have been transmission undetected for an unknown duration followed by recent amplification events”.
Rosamund Lewis, the WHO’s technical lead for monkeypox, said in a Wednesday briefing last week that this undetected transmission could last “weeks, months or even years”.
Amesh A. Adalja, senior researcher at the Johns Hopkins Center for Health Security, told NBC News last weekend: “What probably happened was that an infectious disease endemic to Africa happened. found in a social and sexual network, then was greatly helped by big amplification events, like raves in Belgium, to be broadcast around the world.”
Adalja added that skin tags associated with monkeypox are mistaken for other sexually transmitted infections that could delay diagnosis.
Meanwhile, scientists are scrambling to better understand if there was a genetic modification to the virus that could have allowed it to start spreading outside of Africa more efficiently than before.
Monkeypox is a disease caused by a virus of the same name that was first discovered in monkeys for animal testing in 1958. The first human case was detected in 1970.
Symptoms of the disease are similar but milder than smallpox. The incubation period – the interval between infection and symptoms – is usually six to 13 days.
Symptoms usually start with fever, headache, body aches, swollen lymph nodes and lack of energy, according to the WHO. During the day or a few days after the fever, a rash appears that can affect various parts of the body.
Symptoms usually last two to four weeks. Historically, the case fatality rate of monkeypox has ranged from zero to 11% in the general population, although lately it has been around 3-6%.
Monkeypox can be spread between people through direct contact with infectious sores, scabs, or bodily fluids. According to the US Centers for Disease Control and Prevention (CDC), it can also be spread through prolonged face-to-face contact as well as during sex.
It is not known whether it can be spread through semen or vaginal secretions.
The disease can also be spread from animals to humans, for example through a bite or scratch or through handling wild game. More information about the transmission can be found on the CDC’s website.
The current and ongoing outbreak is the first time that many cases of monkeypox have been reported at the same time in non-endemic countries around the world. Cases so far have mostly, but not exclusively, involved men who have sex with men.