The monkeypox virus has mutated at a far faster rate than would normally be expected and likely underwent a period of "accelerated evolution,"a new study suggests.

The virus, which has infected more than 3,500 people in 48 countries since its detection outside Africa in May, may be more infectious due to dozens of new mutations. In all, the virus carries 50 new mutations not seen in previous strains detected from 2018 to 2019, according to a new study published June 24 in the journal Nature Medicine(opens in new tab). Scientists usually don't expect viruses like monkeypox to gain more than one or two mutations each year, the study authors noted.

Monkeypox is a rare disease that virologists think may naturally circulate in monkeys and rodents. An orthopoxvirus, it comes from the same family and genus as the variola virus, which causes smallpox, and doesn't usually spread far beyond West and Central Africa, where it is endemic. This year, however, the first widespread outbreak of the disease spread beyond Africa, surprising scientists and leading the World Health Organization (WHO) to begin considering whether to classify the outbreak as a global health emergency.