Molecular detection and characterization of lumpy skin disease viruses from outbreaks in Thailand in 2021

Lumpy skin disease (LSD) is one of the most important transboundary and emerging diseases in cattle. The disease causes significant economic losses in animal production and trade worldwide. The first LSD outbreak was recorded in March 2021, at Roi-Et province in the northeastern region of Thailand. Thereafter, the disease had rapidly spread into neighbouring provinces and throughout the country. The aim of the present study was to provide information regarding to the molecular detection and characterization of LSD viruses from outbreaks in Thailand in 2021. There were 1,748,112 susceptible and 604,404 affected animals (n = 588,512 [36.30%], beef cattle; n = 12,367 [15.74%], dairy cattle and n = 3524 [7.35%], buffaloes). The morbidity and mortality rates were 34.57% and 3.47%, respectively, and the case fatality rate was 10.05% (60,713 deaths). Based on real-time polymerase chain reaction results, the p32 gene of LSD virus (LSDV) was detected more frequently in skin nodule samples (54/77, 70.13%) than in nasal swabs (26/55, 42.57%) and EDTA blood (16/77, 20.78%) samples. Moreover, the copy number of the p32 gene was higher in skin nodule samples than in nasal swab and EDTA blood samples (cycle threshold value = 21.94 ± 0.62 vs. 31.52 ± 0.66 and 34.27 ± 0.32, respectively). Furthermore, 29 (53.70%) of 54 capripoxvirus-positive skin nodule samples were successfully isolated from Madin-Darby bovine kidney cells, and the cytopathic effect was observed 72 h after inoculation. Based on the phylogenetic trees of the GPCR, ANK and RPO30 gene sequences, the LSDV isolates from Thailand were distinct from both the LSDV-field and LSDV-vaccine groups and were closely correlated with the LSDV strains isolated from mainland China, Hong Kong territory and Vietnam in 2020. Additionally, they could be a potential virulent vaccine-recombinant LSDV strain.