CDC Issues Warning on More Severe Strain of Monkeypox

The Centers for Disease Control and Prevention (CDC) headquarters in Atlanta on April 23, 2020. Tami Chappell/AFP via Getty Images

The U.S. Centers for Disease Control and Prevention (CDC) issued a health alert on Thursday about the emergency of a more severe sub-variant of the monkeypox, or mpox, virus.

The CDC issued an alert about the possibility of a subtype of the mpox virus called Clade I in travelers who have been in the Democratic Republic of Congo, adding that the clade is generally more infectious and leads to more severe infections than another subtype called Clade II.

Clade I has not yet been reported in the United States at this time, the CDC added, saying that recent evidence has shown for the first time Clade I can be transmitted through sexual contact, which has proved to be the main transmission mode for the less deadly strain of the disease that broke out globally last year.

It was previously thought that both types of monkeypox, which causes flu-like symptoms and pus-filled skin lesions, spread mainly through close contact among humans after spilling over from an infected animal through bites, scratches, hunting, or cooking.

Clade I “has previously been observed to be more transmissible and to cause more severe infections” than the variant that spread primarily among gay males in 2022 and 2023, known as Clade II.

The UN’s World Health Organization (WHO) last month said that 11 out of 26 provinces of the DR Congo “are identified as endemic for mpox, but in more recent years the total number of mpox cases and the number of provinces reporting mpox has been expanding, to 22 provinces as of November 2023.”

“The virus variant is known to be more virulent. If it adapts better to human-to-human transmission, that presents a risk,” Rosamund Lewis of the WHO’s monkeypox surveillance team told Reuters.

The country has not requested any treatments, Ms. Lewis said. Getting the vaccine is more complex, she added, because only one region of the WHO has a supply agreement in place. Any donations would also need funding for deployment.

WHO officials say the DR Congo has reported over 13,000 cases in 2023, more than twice as many as during the last peak in 2020. It added that it’s working with local authorities on the response and a risk assessment.

Travel Alert

In a travel bulletin, the CDC advised Americans traveling to the country to exercise heightened caution, adding that they should avoid contact with sick people, stay away from wild animals, and refrain from consuming game meat.

“Seek medical care immediately if you develop new, unexplained skin rash (lesions on any part of the body), with or without fever and chills, and avoid contact with others,” the Dec. 7 travel advisory from the agency also said. “Tell your doctor if you traveled to the DRC in the month before developing symptoms.”

Since January, the DR Congo has reported about 12,569 suspected monkeypox cases and 581 deaths, or 5 percent of suspected cases, the CDC said.

WHO Statement

In November, WHO said in a statement that a resident of Belgium traveled to the DR Congo in March and tested positive for the virus shortly thereafter, adding that the man “identified himself as a man who has sexual relations with other men.”

Among his contacts, five others later tested positive for monkeypox, said the WHO.

“This is the first definitive proof of sexual transmission of monkeypox in Africa,” Oyewale Tomori, a Nigerian virologist who sits on WHO advisory groups, told The Associated Press. “The idea that this kind of transmission could not be happening here has now been debunked.”

He added that “we have been saying for years in Africa that monkeypox is a problem,” saying: “Now that sexual transmission has been confirmed here, this should be a signal to everyone to take it much more seriously.”

This 2003 electron microscope image made available by the Centers for Disease Control and Prevention shows mature, oval-shaped monkeypox virions (L) and spherical immature virions (R) obtained from a sample of human skin associated with the 2003 prairie dog outbreak. Cynthia S. Goldsmith, Russell Regner/CDC via AP

WHO’s statement added that the risk of the virus spreading to other countries in Africa and worldwide “appears to be significant” and that there could be “potentially more severe consequences” than the prior outbreak.

“A concurrent outbreak of mpox is occurring in the neighboring Republic of Congo along the Congo River ecosystem, whose links, if any, with cases in the Democratic Republic of the Congo remain unknown,” said WHO in its statement.

Earlier this year, WHO confirmed it was ending a 10-month-long global health emergency for monkeypox, coming after it declared the virus a public health emergency of international concern in July 2022 and backed its stand in November and February. In late 2022, WHO issued a recommendation to rename monkeypox to mpox “following a series of consultations with global experts.”

Reuters contributed to this report.