The U.S. identified its first case this year of the monkeypox virus, adding to a growing number of confirmed and suspected infections in the U.K., Portugal and Spain.

The Massachusetts Health Department reported on Wednesday the case of an adult male who had recently traveled to Canada, where more than a dozen monkeypox infections have been identified. The man traveled via private transportation, according to the U.S. Centers for Disease Control and Prevention, which said it’s working with Massachusetts health officials on monitoring the situation.

Monkeypox is a rare but potentially serious viral illness that usually begins with flu-like symptoms before progressing to a rash, which could be confused with sexually transmitted infections like syphilis or herpes. Infections usually last from two to four weeks, according to the CDC.