Belgium has become the first country to issue a mandatory 21-day Monkeypox quarantine for those who contract the virus, The Daily Mail reports. Additionally, a White House official warned Sunday that more cases would likely emerge.

Belgian health authorities told news outlets earlier this week that those who contract the virus will have to self-isolate. But individuals who have had close contact with the virus won't be required to self-quarantine. Still, they warn, such individuals should stay vigilant if they have come in contact with vulnerable people.

A fourth case of the virus was reported in Belgium on Saturday, said Emmanuel Andre, the official in charge of the National Reference lab for COVID-19 in Belgium. Referring to a festival that took place earlier this month, Andre wrote that "this patient is being treated in Wallonia and is linked to the Antwerp event in which two other people were infected."

Monkeypox is a virus related to smallpox originating from Africa. Its symptoms include a bumpy rash, a fever, sore muscles, and a headache. It is, however, less deadly than smallpox, and health officials have stated its mortality rate is around 4%.

Experts have still expressed concern about monkeypox's spread beyond Africa in recent days.

"I would not be surprised if we see a few more [monkeypox] cases in the upcoming days. And I think the president's right, anytime we have an infectious disease outbreak like this, we should all be paying attention," White House COVID-19 coordinator Ashish Jha told ABC News on Sunday.

The administration is "confident we're going to be able to get our arms around it … but we're going to track it very closely and use the tools we have to make sure that we continue to prevent further spread and take care of the people who get infected," he added.

A Saturday update from the World Health Organization (WHO) said so far there have been 92 confirmed cases in 12 different countries, among them include the United Kingdom, Italy, Sweden, Portugal, Belgium, Germany, France, Spain, the United States, Australia, and Canada.

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