Molecular Characterization and Epidemiology of Lumpy Skin Disease Virus in Bhutan, 2023

Lumpy skin disease (LSD) is a disease of cattle and other ruminants caused by the LSD Virus (LSDV). LSD infections are characterized by high morbidity, low mortality, and significant economic impact. Initially endemic to Africa only, LSD has spread to the Middle East, Europe, and Asia in the past decade. In 2023, LSD posed a significant threat to Bhutan's livestock population, with outbreaks reported across 20 Dzongkhags (districts) and 192 Gewogs (groups of villages). This study investigated the epidemiology and molecular aspects of the outbreak. A total of 19,907 animals (16,728 cattle and 3179 yaks) were affected, with 2888 deaths recorded, leading to an apparent case fatality rate (CFR) of 9.92% in cattle and 38.66% in yaks. Molecular characterization of the LSDV-positive samples from cattle and yaks based on LSDV-differentiating genes (i.e., RPO30, GPCR, EEV, and B22R) revealed 100% similarity among the samples, clustering them with LSDV field isolates from Sudan, India, and China in Clade 1.2. Further whole-genome sequence characterization of a representative sample (LSDV_Bhutan_03) from cattle skin scrapings and phylogenetic network analysis clustered the virus with Neethling Warmbaths (NW)-like LSDVs (Clade 1.2.2). Within the NW-like clade, the Bhutan LSDV was closely related to recent isolates from cattle and buffalo in India and yaks in China. These data highlight the importance of LSDV surveillance in both domestic and wild bovines to identify spillover incidences, understand the extent of disease spread, and strengthen control measures.