Development of a Synthesized Gene Unique to Lumpy Skin Disease Virus and Its Application in Serological Differentiation of Naturally Infected from Vaccinated Cattle with Attenuated Goat Pox Vaccine

Lumpy skin disease (LSD) is an important infectious disease caused by lumpy skin disease virus (LSDV) in bovine. LSDV, sheep pox virus (SPPV), and goat pox virus (GTPV) from the same genus Capripoxvirus (CaPV) of the Poxviridae family exhibit a nucleotide sequence similarity of up to 97%. Therefore, attenuated vaccines of GTPV and SPPV are often used to vaccinate cattle against LSD. However, available serological testing methods cannot accurately differentiate cattle vaccinated with GTPV from those infected with LSDV, posing a significant risk for disease spread. In this study, we developed a synthesized gene unique to LSDV as a differential antigen to detect serum antibodies specific to LSDV and differentiate naturally infected from vaccinated animals (DIVA). We used it for an in-house indirect enzyme-linked immunosorbent assay (iELISA), and no cross-reaction with positive sera for bovine viral diarrhea virus (BVDV), infectious bovine rhinotracheitis virus (IBRV), Mycobacterium bovis (M. Tb), Pasteurella multocida (P. multocida), and Mycoplasma bovis (M. bovis). The cut-off value (S/P%) was 30% for in-house iELISA. The corresponding diagnostic specificity was 100% (95% CI: 88.43–100), and the diagnostic sensitivity was 93.3% (95% CI: 77.93–99.18). The intra-assay coefficient of variation (CV) ranged from 1.08% to 4.11%, and the interassay CV was 0.00%–8.90%. Furthermore, 200 clinical serum samples were examined, in the vaccinated herd, there were no positive samples (0/141) indicating the strong differentiation ability of this method. On the other hand, in the infected herds, the overall positivity was 33.90% (20/59) (95% CI: 22.08–47.39). In summary, a valuable synthesized protein unique to LSDV was developed and showed a promising application in an iELISA with high specificity and sensitivity in differentiating cattle infected with LSDV from those vaccinated with GTPV.