The second case of monkeypox in the United States this year was identified in a Maryland resident who had recently returned from Nigeria, health officials said. The risk of the virus spreading was low.
The Maryland Department of Health said in a statement that the person was in isolation with mild symptoms. The traveler was not identified by the agency.
The United States has had two confirmed cases of monkeypox in the past few months. The Centers for Disease Control and Prevention said in July that the first case of the disease was discovered in a Texas resident who had returned from Nigeria.
The C.D.C. said it was working with an airline and health officials to reach anyone who may have been in contact with the Maryland traveler. The agency said that fellow passengers had a low chance of contracting the coronaviruses because they were required to wear masks.
The Maryland health authorities said in a statement that there was no need for special precautions for the general public.
The C.D.C. said that Monkeypox is mostly found in Central and Western Africa, although it caused an outbreak in the United States in 2003 after it spread from imported African rodents to pet prairie dogs.
There were 47 confirmed and probable cases of monkeypox in six states during that outbreak. The people who were infections reported symptoms such as a rash and headaches. There were no deaths reported.
The C.D.C. says that Monkeypox causes milder symptoms than smallpox, but it develops into a rash on the face and body. The majority of infections last two to four weeks.
The C.D.C. showed that the patient had been exposed to a strain of monkeypox most commonly seen in parts of West Africa, including Nigeria. Infections with that strain are fatal in about 1 in 100 people.
The C.D.C. said it had supported Nigeria in its response to monkeypox, which reappeared in the country after a long time without any reported cases. In Nigeria, 218 cases have been identified and eight have been reported in international travelers from the country.
There are no specific treatments for monkeypox infections, according to the C.D.C., although one vaccine has been licensed in the United States to prevent monkeypox.
People who are bitten or scratched by an animal, or who come in contact with an animal that is sick, can be exposed to monkeypox.
The virus can be spread through bodily fluids, but it is usually transmitted through large respiratory droplets that do not travel more than a few feet. The C.D.C. said that face-to-face contact is necessary for the spread of the virus.
