About
- Level: Laboratory Advisory
- Audience: Clinical Laboratory Professionals
LOCS message
A recombinant monkeypox virus (MPXV) infection was reported in early December 2025 in a resident of the United Kingdom following travel to Asia. Viral sequencing revealed that the sample contained genetic characteristics of both clade I and clade II MPXV. The case had a disease presentation similar to other MPXV cases, and the risk to the general population remains low.
Before this case, there have been more than 150,000 cases of clade I and clade II monkeypox reported globally since 2022, but no MPXV clade I/II co-infections had been reported anywhere in the world. No additional cases of the recombinant virus have been identified, and it is unclear exactly where it may be circulating.
Because viruses with large genetic changes (including recombinant viruses) may impact PCR tests, CDC recommends a testing approach initially using a generic orthopoxvirus or monkeypox virus (MPXV) test that targets a conserved area of the viral genome. The recently detected recombinant virus may impact interpretation of clade-specific tests. CDC encourages laboratories and test manufacturers to use in silico analysis to examine the published sequence of the recombinant virus to predict results for any laboratory-developed or commercially available tests. The CDC non-variola orthopoxvirus (NVO) test used in many public health laboratories and some commercial laboratories will detect this recombinant.
CDC recommends performing clade-specific testing in all monkeypox cases that meet any of the criteria below:
1) Severe cases (hospitalized)
2) Cases in vaccinated persons
3) Cases not associated with MSM populations
4) Cases with travel from locations with known recent clade I MPXV cases or exposure to an individual who traveled from locations with known recent clade I MPXV cases
5) For 3 months after a clade I MPXV detection in the locality
6) Locally acquired cases in localities that have not had monkeypox in the last 6 months
7) Laboratory results consistent with suspect clade I or recombinant virus: --Positive result by MPXV or orthopoxvirus generic test AND negative or indeterminate result by clade II-specific test --Positive clase I AND Clade II results in a single case sample
Laboratories should follow requirements of the Federal Select Agent Program if they detect clade undetermined or a clade I virus, including the recombinant virus containing clade I MPXV genetic material. Facilities using CDC's NVO test that are not performing their own MPXV clade-specific testing should continue submitting the duplicate specimen from patients with positive NVO test results to CDC. Some non-CDC laboratories have other options for clade-specific testing (e.g., molecular testing or genetic sequencing). These laboratories should alert their state health department and CDC (poxvirus@cdc.gov) if results indicate detection of clade I MPXV.
Additional guidance
If questions about the predicted test results with this recombinant when using a commercial test, please contact the specific test manufacturer.
Refer to HAN Health Update 516 for the most recent CDC clinical and travel guidance on clade I monkeypox. Clinicians should know symptoms of MPXV infection and ask patients about recent travel history and other risk factors and consider MPXV testing. Suspected and confirmed cases caused by clade I MPXV should be reported to the local, territorial, and state public health authorities as soon as possible. CDC recommends vaccination to people who are eligible for monkeypox vaccine, including those who may have a recent MPXV exposure.
We encourage you to share this message widely with your network(s).
Opt in to receive updates from the CDC Laboratory Outreach Communication System.
Resources
- About Monkeypox | CDC
- Prevention Strategies for Monkeypox, including Vaccinating People at Risk via Sexual Exposure, for U.S. Travelers Visiting Countries with Clade I Monkeypox Outbreaks | HAN
- Clinical Features of Monkeypox | CDC
- Diagnostic Testing for Monkeypox | CDC
- Clinical Overview of Clade I and Clade II Monkeypox | Monkeypox | CDC
- FAQ: Outbreaks | Compliance | Federal Select Agent Program
Contact us
Please use the information below if you have any questions.
- If you are a clinical or public health laboratory professional, contact LOCS.
- For media inquiries, contact the CDC Newsroom.
- For all other questions, contact CDC-INFO.
Thank you,
The Laboratory Outreach Communication System
Laboratory Outreach Communication System (LOCS)
Office of Laboratory Systems and Response (OLSR)
Centers for Disease Control and Prevention (CDC)
LOCS@cdc.gov
www.cdc.gov/locs/php/about