Detected cases of monkeypox have doubled in the United Kingdom to 20 since early May, and several suspected cases are being investigated in the United States. One U.S. case, in a man in Massachusetts, has been confirmed.
The outbreaks represent a rare appearance of the disease in Europe and North America. Monkeypox has been known from Central and West Africa since 1970, according to the Centers for Disease Control and Prevention (CDC). It causes fever, muscle aches, chills and full-body, chickenpox-like rash made up of fluid-filled pustules.
The disease is related to smallpox, and health officials have tackled previous, travel-related spread of monkeypox with a strategy called "ring vaccination." Close contacts of a person with the disease are vaccinated with the smallpox vaccine. The smallpox virus is related to the monkeypox virus, and vaccination with the smallpox vaccine is at least 85% effective against monkeypox, according to the CDC.
Health officials are currently trying to work out the chain of transmission behind the new clusters of the disease. The number of confirmed cases in the U.K. rose from nine to 20 on Friday (May 20), according to Reuters. Officials confirmed a case in a man in Massachusetts who recently traveled to Canada, according to CNN. U.S. health officials are also investigating a possible monkeypox case at Bellevue Hospital in New York City, according to ABC7NY. Canada, Italy, Sweden, Portugal and Spain have all reported monkeypox clusters, with Spain reporting that the majority of cases are linked to an adult sauna in Madrid, according to Reuters.
Monkeypox typically requires sustained contact with an infected person in order to spread, according to the CDC. In most cases, the disease resolves on its own, though the fatality rate in modern times has ranged between 3% and 6%, according to the World Health Organization.
There are two distinct strains of the virus. The Congo strain, which is more virulent, has historically killed up to 10% of people infected, while the West African strain causes fatalities in 1% of cases. Genetic sequencing has revealed that the strain found in the U.K. is the less-deadly West African version of the virus.
According to the WHO, there were two cases of monkeypox in the United States in 2021, both related to recent travel to Nigeria, which has been experiencing an outbreak since 2017. The last significant outbreak of monkeypox in the United States was in 2003, when 47 human cases were linked to pet prairie dogs that caught the virus after an Illinois pet vendor housed them near the cages of small African mammals, the CDC reported.
Originally published on Live Science.
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Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.