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An outbreak of Clade I mpox virus is currently spreading in the Democratic Republic of the Congo (DRC), and clinicians should be aware of the potential for transmission from people traveling from the Central African country, the CDC said Thursday in a .

Of the two distinct mpox subtypes, Clade I is endemic in Central Africa, and appears to be more transmissible and causes more severe infections than the Clade II subtype. So far, no Clade I mpox infections have been detected in the U.S. during surveillance testing. The current threat for Clade I mpox in travelers remains low, the CDC said, in part because there are no direct commercial flights to the U.S. from the DRC.

However, suspicion for infection should be high for people who have been in the DRC within the last 21 days and who have symptoms consistent with mpox, such as diffuse rash and lymphadenopathy.

Clade IIb mpox was associated with the global outbreak in 2022-2023, and occurred predominantly among gay, bisexual, and other men who have sex with men (MSM). Clade I mpox can spread by human-to-human contact, but has previously been associated with non-sexual routes of transmission.

According to the , from Jan. 1 through Nov. 12, 2023, a total of 12,569 suspected mpox cases were detected in the DRC -- the highest number of annual cases ever reported and a substantial increase over the median annual number of suspected mpox cases reported from 2016 to 2021.

The overall case fatality rate has been calculated at 4.6%, with some regions of the DRC reporting higher rates. In comparison, the case fatality rate during the mpox outbreak of 2022 was just 0.18%, before the outbreak of the Clade I subtype.

Mpox should be considered in patients presenting with rashes with or without fever. Lymphadenopathy may be present. Lesions can be variable in presentation, and can be firm and rubbery, deep-seated, and well-circumscribed, or large, with diffuse, centrifugal lesion distribution, the CDC said.

If mpox is suspected, clinicians should consult with their state health departments to determine testing options. If clade-specific testing is not available, the CDC strongly encouraged clinicians to submit specimens directly to the CDC, coordinated through local or state health departments. Clinicians should submit lesion specimens following specimen collection guidelines, including collection of two swabs per lesion to ensure an adequate sample. Lesions should not be aspirated or unroofed due to the risk of injury with sharp instruments.

Currently, there are no specific treatments for mpox, but the same medical countermeasures used for Clade II mpox treatment and prevention are likely to be effective for the Clade 1 subtype, the health advisory noted. According to the the antiviral medications tecovirimat (Tpoxx) and brincidofovir (Tembexa) have been shown to be effective against orthopoxviruses. Tecovirimat is recommended as a first-line option. Vaccinia immune globulin intravenous can also be used as treatment in severe cases or for prophylaxis in people who have severe immunodeficiency in T-cell function and who have been exposed to mpox.

The CDC also said that the two available vaccines in the U.S. -- Jynneos, approved for mpox and smallpox, and ACAM2000, approved for smallpox -- will be effective in providing antibodies that are cross-protective for Clade 1 mpox.

The recommends that adults with risk factors for mpox be vaccinated with the 2-dose Jynneos regimen. However, vaccination coverage in the U.S. remains low, with only one in four people who are eligible to receive the vaccine having received both doses of Jynneos, the CDC said. They recommended that clinicians encourage people who are eligible for the vaccines to get vaccinated against mpox.

There are no recommendations for vaccination for travelers to and from the DRC who do not have risk factors for mpox. However, the CDC has issued a for people traveling to the DRC.

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