There is a new strain of clade I monkeypox (mpox), the more lethal variety, which is unlikely to be distinguished from clade II with the existing CDC-approved assay. Clade I mpox is now present in two countries, the Democratic Republic of the Congo and the adjacent Republic of the Congo. It is spreading via heterosexual contact from prostitutes to their male customers and from these male customers to their families. This means at least two things: 1. Clade I mpox, which has a case fatality rate of about 4 – 8%, is spreading more readily and is crossing borders. 2. Anyone using the CDC primers will not be able to determine whether someone is infected with Clade I or Clade II. Thus, most doctors, who have not been alerted to this change by the CDC, will assume that anyone who has been infected with monkeypox has the less lethal Clade II strain. Hence, it is likely that when, not if, Clade I starts to spread in the US, we will have no warning.
The key paper describing the new Clade I variant is:
“Ongoing mpox outbreak in Kamituga, South Kivu province, associated with monkeypox virus of a novel Clade I sub-lineage, Democratic Republic of the Congo, 2024”
Masirka et al. Eurosurveillance March 14, 2024
https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2024.29.11.2400106
I will include some excerpts of this paper with my interpretations:
In the Democratic Republic of the Congo (DRC), the numbers of people with suspected infection with monkeypox virus (MPXV), the virus that causes mpox, have increased since the start of 2023. A total of 12,569 suspected mpox cases have been reported up to 12 November, the highest number of annual cases ever recorded [1]. The case fatality rate has been estimated at 4.6% [1]; moreover, new cases have occurred in geographical areas of the country where the disease was previously not observed, such as Kinshasa and South Kivu province [1,2]. Despite this concerning situation, there is only limited genomic information available on the circulating viruses, which suggests that they belong to Clade I.
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At the time of writing, no near-complete sequences of MPXV circulating in DRC from the 2023 outbreak were available on (public) online databases.
Clade I monkeypox, with a case fatality rate of 4.6%, is spreading more efficiently in humans in the Democratic Republic of the Congo. Public sequence information on this strain of virus is insufficient.
The six sequences from the current study grouped with published Clade I sequences, but in a distinct sub-lineage from all other Clade I sequences, suggesting that the ongoing outbreak in South Kivu results from a separate introduction ( Figure 1 and Supplementary Figure 1 and 2 ). The six sequences have several single nucleotide polymorphism (SNP) differences between them, which suggests ongoing circulation of this outbreak strain for some time already.
This is a previously undocumented strain of Clade I sequence. It has been circulating undetected in the Democratic Republic of the Congo for some time.
While the generic primers and probe still seem to be functional with only one mutation in the reverse primer, the specific Clade I virus real-time PCR target, recommended by the US CDC, is absent in the genomes of the novel MPXV strains ( Figure 2 and Supplementary Figure 3). The observed deletion is 1,114 nt in size and results in the complete deletion of the OPG032 gene. The coverage of this region ranged between 76× and 941× sequence reads depending on the sample. Due to the deletion, the rapid US CDC method to identify Clade I in newly diagnosed mpox cases is most likely not reliable for detection of the novel sub-lineage identified in the current study.
The newly reported Clade I variant has a deletion of over 1,000 base pairs which includes a gene which had previously been thought to be deleted only in Clade II mpox. Generic primers, which are used to determine whether a patient has been infected with mpox should work on the new strain. However, CDC primers designed to distinguish between Clade I and II will not function properly.
In DRC, where human infection with MPXV was first ever recognised in 1970, sporadic mpox outbreaks have been reported since, with increasing frequency over time [17]. The particular rise in the number of suspected MPXV cases recorded in the country in 2023, and their occurrence in unusual geographic areas [2] suggests a possible change in the characteristics of the virus and the epidemiology of the disease.
The changes in the sequence of Clade I mpox may have resulted in an increased ability to spread human-to-human.
From the mpox outbreak in Kamituga, South Kivu, six near-to-complete MPXV sequences derived from local patients hospitalised with mpox were obtained. Phylogenetic analyses of these sequences together with those available for other Clade I and II viruses, placed them in a new sub-lineage near the root of Clade I, which suggests that the outbreak in this region results from a new introduction, most likely from a zoonotic reservoir. Although sequences from a small 2023 Kinshasa outbreak are not publicly available, the placement of those sequences in a published phylogenetic tree [3] suggests that the Kamituga outbreak is not related to the outbreak in Kinshasa. Our findings therefore suggest that there are at least two independent outbreaks ongoing in DRC.
Remarkably, a large stretch of sequence in the genomes belonging to the novel MPXV sub-lineage was absent compared to other Clade I genomes, which would lead to failure of the Clade I-specific real-time PCR recommended by the US CDC [15]. A deletion in the same region is also observed in Clade II MPXV, and this was the basis for clade assignment using the CDC PCR. Therefore, if the viruses from the new lineage were to spread internationally, this molecular surveillance tool can no longer be used to rapidly identify these Clade I virus infections while the global Clade IIb outbreak is ongoing.
It is surprising that the same deletion previously reported in Clade II is now observed in Clade I. This was completely unexpected by the CDC. So much so that they actually used this deletion to distinguish between Clade I and Clade II which is why their primers will fail to make this distinction with the new strain.
Altogether, the findings of this study strongly suggest that whole genome sequencing of a larger subset of MPXV currently causing mpox cases in DRC, as well as public data sharing, are essential to understand the ongoing epidemic. Further studies, sequencing and analyses are ongoing, but in accordance with the above statement we believe that rapid public sharing of all available information is essential to help to better understand and contain the current mpox emergence.
PCR is an insufficient tool with which to examine the rapidly changing nature of the mpox epidemic.
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Suggestion: I know CDC leadership will approach this issue at their normal glacial pace. But could someone wake the President and tell him that something serious is going on in Africa? Remind him what happened to the last President who botched a pandemic response, come election time.