Characteristics of MPXV
MPXV has the typical rectangular shape and size of other poxviruses such as Smallpox, with a size of approximately 200 × 250 nm [10]. It has a dumbbell-shaped core with lateral bodies and the surface membranes show surface tubules or filaments [11] (Fig. 2). MPXV is an enveloped double-stranded DNA virus with approximately 197kb of genomic DNA encoding up to 280 genes and contains about 190 nonoverlapping open reading frames (ORFs, >180 nucleotides) [12,13]. As shown in Fig. 3, the genome of MPXV consists of a large conserved central genomic region with variable regions containing inverted terminal repeats (ITRs) at both ends [14]. Except for four ORFs located in the ITRs, all ORFs are present in the central region of the genome[15]. The non-conserved genes of MPXV, located in the variable regions at both ends, are most host range and virulence genes, which are mainly involved in MPXV immune escape [16,17]. In contrast, the genes in the central genomic region of MPXV are relatively conserved and encode structural proteins and essential enzymes [12]. The genome-wide analysis confirmed that there are two clades of MPXV: the Central African (Congo Basin) clade and the West African clade [18]. However, to avoid discriminatory geographical identification, the WHO announced the renaming of the MPXV clades on August 12, 2022, with new names consisting of Roman numerals and lowercase English letters. The experts convened by WHO referred to the previous Central African clade as Clade I and the previous West African clade as Clade II. Clade II includes two subclades, IIa and IIb, with IIb being the main group of virus variants transmitted in the 2022 Mpox outbreak. [19,20]. Clade I and Clade II are genetically different and have different toxicity and case fatality rate, 10.6% and 3.6%, respectively [18,21–23]. The genomic comparison revealed that the nucleotide divergence between the two clades was 0.55-0.56%. The Clade I had 173 unique functional genes, while the Clade II had 171. Of the 56 virulence genes, 53 viral genes were shared by the two clades. The most striking differences between these two clades are in the gene orthogonal of BR-203, BR-209, and COP-C3L [21].