D.C. Health has reported the first positive orthopox case in a resident who recently traveled to Europe, and it sent samples to the Centers for Disease Control and Prevention to test for monkeypox, the agency said Sunday.
The patient is isolating and doesn't pose a risk to the public, and the agency is monitoring close contacts, it said in a release.
The orthopox family of viruses includes monkeypox, D.C. Health said.
The first case of monkeypox in the U.S. this year was reported in Massachusetts.
Monkeypox is a cousin of the smallpox virus and causes similar, but milder, symptoms in humans, according to the CDC.
The incubation period from the time a person is exposed to when symptoms first appear can be anywhere from five to 21 days, according to the World Health Organization.
Typically, the disease begins with a fever, headache, fatigue, chills and muscle aches. Unlike smallpox, however, monkeypox also causes swollen lymph nodes.
ABC News' Chad Murray contributed to this report.