Epidemiology of lumpy skin disease in Northeast India and a new method for rapid field diagnosis.

Lumpy Skin Disease (LSD), a viral disease affecting cattle and related species, entered India in 2019, with first outbreak reported in Odisha, and has since caused significant economic losses to the Indian livestock sector. Following its entry, the disease spread rapidly to various states, including the northeastern region which is known for its porous borders. A total of 56 clinical samples (whole blood, skin scrapings, nasal swab, skin lesions and serum) were collected from various outbreaks of LSD in Meghalaya. World Organisation for Animal Health (WOAH)-recommended probe-based real-time polymerase chain reaction (PCR) targeting LSDV126 region detected Lumpy skin disease virus (LSDV) in 42 out of 56 clinical samples. Additionally, 182 contemporary serum samples were screened using commercial ELISA kit which indicated an apparent seroprevalence of 11.54% (95% confidence interval [CI] 7.7-17%) and a true prevalence of 12.3% (95% CI 7.86-18.53%). Three representative samples were subjected to partial sequencing-based phylogenetic analysis targeting the LSDVp32 and LSDV117 regions which confirmed the diagnosis of LSD and also revealed circulation of the Kenyan field strain-associated LSDV. Furthermore, a novel isothermal approach exploiting Saltatory Rolling Circle Amplification (SRCA) mechanism was also explored with WOAH-recommended conventional PCR primers which yielded results comparable to real-time PCR-based diagnostic methods with a minimum detection limit of 10 copies/µL of the standard plasmid. The availability of this rapid and reliable diagnostic assay could be harnessed for early diagnosis of LSD, especially in resource-limited and field laboratory settings and ultimately aid in the timely implementation of control strategies.