LSD is an endemic disease in African and Middle Eastern countries and has recently spread to other countries (Agianniotaki et al., 2017; Al-Salihi & Hassan, 2015; E. S. M. Tuppurainen et al., 2017). India reported LSD for the first time in 2019 from Odisha (Sudhakar et al., 2020) and later the spread has been rapid to other parts of India. In this study, we analyzed the complete genome sequence of LSDV (LSDV/208/PVNRTVU/2020) from a skin biopsy sample collected from a cow exhibiting typical symptoms of LSD. The complete genome was deposited in GenBank (accession number ON400507). To date, a total of 55 complete genomes of LSDV from across the globe. This is the first complete genome sequence of LSDV of 150 Kbp reported from India, 150445 bp long, with a central coding region of 145937 bp and bounded by two identical 2254 bp long inverted terminal repeats, and an overall GC content of 25.9%. A total of 156 genes were annotated and gene ontology was derived (Supplementary Fig. S1).
The complete genome sequence was compared with 15 reference genomes of LSDV, two GTPV and two SPPV (Table S1). The current sequence showed 99.99% identity with Neethling 2490 and KSGP 0240 LSDV and 97.73% identity with GTPV isolate from India (GenBank ID MN072620). Alignment of GPCR, RPO30, EEV and P32 genes with other Indian LSDV showed a 100% identity with both RPO30 and P32 genes, whereas, GPCR and EEV proteins showed amino acid percentage identities ranging between 99.2–100% and 99.4–100%, respectively. Alignment with sequences of three LSDV/Cattle/India/2019/Ranchi-1 passaged in Vero cells, P-10 (GenBank ID OK422492; 146171 bp), P-30 (GenBank ID OK422493; 147681 bp) or P-50 (GenBank ID OK422494; 139051 bp) revealed 100%, 99.3% and 99.3% identities, albeit only with a coverage of 97%, 98% and 93%, respectively.
A 12-nucleotide insertion in the GPCR gene, observed in all the recent outbreaks of LSDV in Asia, in vaccine-related field viruses from South Africa, in historial strains of LSDV from Kenya isolated before 1960s and in recently reported recombinant LSDVs, was also noticed in the current sequence (Fig. 1A). It is interesting to note that this 12 nucleotide insertion is not present in the circulating field strains of LSDV from Africa, Europe and the Middle East (Agianniotaki et al., 2017; Badhy et al., 2021; Chibssa et al., 2021; Krotova, Byadovskaya, Shumilova, van Schalkwyk, & Sprygin, 2022; Sprygin et al., 2018; van Schalkwyk et al., 2020). Additionally, we detected a duplicated region of 27 bp (9 aa) in EEV gene of LSDV/208/PVNRTVU/2020 sequence, similar to that found in field/virulent LSDV strains but absent in LSDV Neethling vaccine-like viruses, Chinese LSDV strain and recombinant LSDV strains identified in Russia (Erster et al., 2019; Sudhakar et al., 2022) (Fig. 1B) indicating the current sequence as a virulent field strain.
Phylogenetic analysis confirmed two independent subgroups, cluster 1.1, which includes strains related to the original Neethling strain (vaccine) and cluster 1.2 which includes field strains (Krotova et al., 2022). The LSDV/208/PVNRTVU/2020 sequence belonged to cluster 1.2 (0.6% divergence with cluster 1.2 strains) and showed 10% divergence with cluster 1.1 strains (Table 1). It closely clustered with Kenyan strains and formed a distinct clade from field strains of Bulgaria, Serbia, Kazakhstan and South Africa (Fig. 2). This reaffirms the speculated route of the virus spread to India (N. Kumar et al., 2021; Sudhakar et al., 2020).
The selection pressure on the genome was less than 1, indicating a purifying selection playing a role in the virus evolution (Miyata & Yasunaga, 1980) (Supplementary Table S2). We found no recombination events however, with reports of LSDV from countries sharing land borders with India (Acharya & Subedi, 2020; Badhy et al., 2021; Flannery et al., 2022; Mathijs et al., 2021; Sudhakar et al., 2020), it is important that such genomic approaches are undertaken to identify any recombinant vaccine like LSDV.
LSD is a rapidly spreading transboundary animal disease (https://www.fao.org/europe/resources/transboundary-animal-diseases-leaflets/en/). With a recent study suggesting a higher rate of genetic changes in the rampant spreading monkeypox virus (Isidro et al., 2022), a member of the same virus family as that of LSDV, a routine and large-scale virogenomic survey for LSDV is warranted. It is worth noting that India presents a heterogeneous population of several breeds of cattle and buffaloes, as well as vector populations and weather conditions, all of which could potentially influence virus maintenance, transmission and evolution. Availability of genomic sequences is needed to understand the dynamics of disease outbreaks and to plan effective strategies for mitigating the spread and future epidemics, which otherwise could pose economic threat worldwide.