ELISA Methods Based on Monoclonal Antibodies for the Serological Diagnosis of Lumpy Skin Disease

Lumpy skin disease (LSD) is a notifiable, transboundary cattle disease that spreads rapidly and has a relevant economic impact. The etiological agent is the LSD virus (LSDV), genus Capripoxvirus, and family Poxviridae. To date, LSDV is widely present in Africa, Asia, and in transcontinental regions like Russia, Turkey, and the Middle East, thus representing a continuous threat to free neighbours. Appropriate serosurveillance programs can complement disease control, inform about its spread, and enable the assessment of vaccination campaigns. Since reliable and practical diagnostic tools could improve serological surveillance, this study aimed to produce and characterize monoclonal antibodies (MAbs) that allowed us to develop ELISA tests for the serological detection of LSD. Four MAbs recognizing a 35 kDa viral protein were selected and used to develop and optimize competitive and indirect ELISAs. Both assays detected seroconversion within 14 days postinfection (dpi) in 18 cattle experimentally infected with LSDV and sequentially sampled for up to 4 weeks. The two novel ELISAs detected also antibodies raised by other capripoxviruses: as observed in cattle, both assays revealed seroconversion within 14 dpi in all nine sheep experimentally infected with sheeppox virus (SPPV), while in eight goats infected with goatpox virus (GTPV) competitive ELISA identified seropositivity earlier and in more animals compared to indirect ELISA. Overall, the sensitivity performance of both developed ELISAs resulted comparatively superior to those of virus neutralization test and the commercial Id.Vet ELISA. Testing of about 200 negative sera from each species recorded a single false-positive cattle in the indirect ELISA, which gave a specificity of 99.5%, whereas for the competitive ELISA, the diagnostic specificity was 100% irrespective of the species tested. The results enable concluding that both new tests correctly detect anti-LSDV antibodies in cattle and can also be reliable tools to recognize antibodies to SPPV and GTPV.