Global cases of the monkeypox virus have surpassed 1,000, the US Centers for Disease Control and Prevention said and urged people to take extra precautions.
As of June 6, 1,019 confirmed and suspected cases of monkeypox have been reported in 29 countries, according to the CDC.
The UK has recorded the most cases, 302 suspected and confirmed infections, followed by Spain (198), Portugal (153) and Canada (80), CNBC reported.
In the wake of rising cases, the CDC also ramped up its alert to a level 2, encouraging people to "practise enhanced precautions" to stem the outbreak, which has spread to 29 non-endemic countries in the past month.
The highest level alert, level 3, would caution against non-essential travel.
Officials at the CDC also suspect that the monkeypox virus may be airborne at least for "short distances" and thus have asked people and healthcare workers in close contact to wear masks.
The CDC on its website has urged monkeypox patients, "especially those who have respiratory symptoms", to wear a surgical mask.
It also asks other household members to "consider wearing a surgical mask" when they are in the presence of the person with monkeypox.
So far health officials have not explicitly addressed the possibility of airborne transmission or the need for masks, but they have emphasised the role of large respiratory droplets that are expelled from infected patients and drift onto objects or people, the New York Times reported.
Moreover, until recently the current outbreak was thought to have derived from the West African strain of the virus, which produces less severe illness than other variants and has a 1 per cent fatality rate.
However, the CDC said that at least two genetically distinct monkeypox variants are currently circulating in the US, which has to date seen 30 cases.
"While they're similar to each other, their genetic analysis shows that they're not linked to each other," said Jennifer McQuiston, deputy director of the CDC's high consequence pathogens and pathology division, at a press briefing.
McQuiston said it is likely that the two strains stem from two different instances where the virus has spilled over from animals to humans in Africa, before spreading via person-to-person contact, the report said.
According to the World Health Organization (WHO), some African countries where the virus is endemic have seen more than 1,400 suspected cases of monkeypox and 56 people have died from it.
Notably, there has been no fatalities reported in the recent outbreak in countries outside Africa.
"This virus has been circulating and killing in Africa for decades," said WHO Director-General, Tedros Adhanom Ghebreyesus, at a press conference in Geneva.
"It's an unfortunate reflection of the world we live in that the international community is only now paying attention to Monkeypox because it has appeared in high-income countries.
"The communities that live with the threat of this virus every day deserve the same concern, the same care and the same access to tools to protect themselves," he noted.