The Massachusetts Department of Public Health reported on Wednesday that a man who traveled to Canada has been diagnosed with a rare and potentially fatal disease.

This is the first report of monkeypox this year in the United States. Each year, officials in Texas and Maryland recorded one case. A series of unusual clusters in other countries have begun to alarm public health officials.

Nine monkeypox cases have been identified in Britain in the past few weeks. Only one patient recently traveled to Nigeria, where a strain of the monkeypox virus has been commonly seen, while the remaining British patients may have acquired the infection through community transmission. Three people lived in a household.

There are 23 suspected cases in Spain. Five cases have been confirmed by Portugal. An infectious disease specialist who was familiar with the effort but was not authorized to discuss it publicly said that Canadian health officials were investigating at least 15 possible cases in Montreal.

The fact that it is in the U.K. in multiple unrelated clusters, plus Spain, and Portugal, is a surprise.

Monkeypox can be treated with an antiviral drug that is similar to the one used to treat smallpox. Monkeypox does not usually cause large outbreaks.

Dr. Inglesby said that clinicians should be aware of the symptoms so that they can detect new cases.

The first signs of a monkeypox infection are body ache and a high temperature. Its most recognizable feature is a rash that starts with red marks and then gets raised and filled with pus.

The skin on the face, chest, and palm is very soft.

In parts of Central and West Africa, the virus can be spread by bites or scratches from rodents. According to the World Health Organization, contact with live and dead animals through hunting and consumption of bush meat are known risk factors.

Dozens of cases of monkeypox were reported in the United States. All were thought to have been caused by exposure to prairie dogs and other pets.

The virus can be spread through body fluids, contaminated objects or respiratory droplets if a person is bitten. The majority of the cases reported in Britain and Canada were among men who have sex with men.

These latest cases, together with reports of cases in countries across Europe, confirm our initial concerns that there could be spread of monkeypox within our communities.

Experts said that men in those communities should watch out for skin eruptions on their genitalia.

The Centers for Disease Control and Prevention and the patient's health care providers are working together to identify people who may have been in contact with him while he was infectious.

The individual is in a good condition in the hospital.