Genetic analysis has suggested that there are two distinct strains of monkeypox in the United States, public health officials said, raising the possibility that cases may have previously gone “under the radar”.
Jennifer McQuiston, an official at the Centers for Disease Control and Prevention (CDC), told reporters on Friday that more research needs to be conducted to determine how long the virus has been circulating in the country.
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“I think it’s certainly possible that there could have been monkeypox cases in the United States that went under the radar previously, but not to any great degree,” she said.
Still, she added, “there could be community-level transmission that is happening” in parts of the US where the virus has not yet been identified.
The CDC said it is likely more cases will be reported.
Dr Angela Rasmussen, a virologist at the University of Saskatchewan in Canada, said the findings suggest that the virus will be harder to contain.
“We don’t really have a good sense of how many cases there are out there,” Rasmussen told The Associated Press news agency.
Monkeypox, which does not usually spread easily among people, is endemic in parts of Africa, where it has been transmitted through bites from small animals.
Last month, Europe and the United States started detecting cases of the virus. Health officials in many countries are investigating monkeypox transmission.
As of Friday, US health authorities had identified at least 21 cases in 11 states. Monkeypox symptoms can include swelling of the lymph nodes, followed by skin rashes.
The US and Europe have not recorded deaths related to monkeypox so far. But Rasmussen warned that infections could turn fatal if they start spreading to vulnerable people.
She added that the virus may start affecting the country’s rodent population even if it is contained among humans. “It’s not out of the question,” Rasmussen said.
New @CDCMMWR: people w/ #monkeypox have been identified in the US CDC has initiated an emergency response to monitor & investigate cases. While monkeypox is rare in the US, people w/ unexplained rashes or lesions should contact their health care provider: https://t.co/R9AsxMCuyx pic.twitter.com/u2m38JHz20
— CDC (@CDCgov) June 3, 2022
The CDC has said its scientists are “tracking multiple cases of monkeypox that have been reported in several countries that don’t normally report monkeypox, including the United States”.
In an advisory to travellers, the CDC has recommended wearing masks and avoiding contact with sick people as well as small animals, including rodents.
It said the risk to the general public is “low” but called on people experiencing unexplained skin rashes to seek medical attention “immediately”.