A fourth monkeypox case has been detected in Belgium, virologist Marc Van Ranst confirms on Twitter.
As in the three previous cases, the fourth case is also linked to the international gay festival Darklands that took place in Antwerp in the beginning of May, Belga News Agency reports.
"It is important that everyone who attended the Darklands Festival remains vigilant for any symptoms," Van Ranst says. "If smallpox lesions are found, a sample can be taken in an emergency department, and close contact with other people should be avoided."
The scale of the outbreak is becoming "clearer and clearer," according to the virologist, and remarks that "this is unheard of before with monkeypox viruses."
The world health organisation (WHO) says it will soon release additional advice on what to do, if one has been in close contact with a person infected with the virus.
Besides Belgium, monkeypox cases have been detected in the Netherlands, Germany, France, The United Kingdom, Italy, Portugal, Spain, Sweden, Canada, U.S, Australia and most recently Israel and Switzerland.
Monkeypox virus is normally found only in West and Central Africa.