Epidemiological and molecular characterization of recombinant clade 2.5 lumpy skin disease virus in beef cattle...

Lumpy skin disease (LSD), caused by lumpy skin disease virus (LSDV), is an economically important transboundary cattle disease that emerged in Thailand in 2021. Despite its rapid nationwide spread, comprehensive epidemiological and molecular information on subsequent outbreaks remains limited. This study investigated LSDV occurrence and associated animal-level factors in Thai beef cattle during the 2022 outbreaks and characterized circulating viruses using molecular and phylogenetic analyses.

A cross-sectional study was conducted from July to December 2022 on 208 beef cattle farms across 27 provinces of Thailand. In total, 482 cattle, including clinically affected and asymptomatic animals, were examined, and 523 samples comprising 387 hair and 136 skin lesion samples were collected. LSDV was detected by polymerase chain reaction targeting the RPO30 gene. Associations between LSDV positivity and epidemiological factors were evaluated using logistic regression. Seventeen representative LSDV-positive samples were selected for RPO30 and GPCR gene sequencing and phylogenetic analysis.

Overall, 358/482 (74.27%) cattle were LSDV-positive, including 304/405 (75.06%) clinically affected and 54/77 (70.13%) asymptomatic cattle. Weaners and calves had higher odds of LSDV positivity than adults, with adjusted odds ratio (aOR) of 1.89 (95% confidence interval [CI]: 1.02-3.69; p = 0.049) and 1.73 (95% CI: 1.01-3.01; p = 0.048), respectively. Vaccinated cattle had lower odds of positivity than unvaccinated cattle (aOR = 0.62; 95% CI: 0.39-0.98; p = 0.041). Skin lesion samples showed higher positivity (91.91%) than hair samples (69.77%). All 17 characterized Thai LSDVs showed 100% nucleotide identity within the RPO30 and GPCR genes and clustered within recombinant clade 2.5, closely related to strains circulating in China and Southeast Asia. A characteristic 12-bp insertion was identified in the GPCR gene.

The high LSDV positivity in both clinically affected and asymptomatic cattle demonstrates widespread viral circulation during the 2022 outbreaks. Younger age was associated with increased positivity, whereas vaccination was protective. The genetic uniformity and clade 2.5 clustering support regional circulation of closely related recombinant LSDVs. These findings emphasize sustained vaccination, molecular surveillance, animal movement control, and regional cooperation for effective LSD prevention and control.