Evaluation of an interferon-gamma release assay for early detection of lumpy skin disease virus infection and vaccination in cattle.

Lumpy skin disease virus (LSDV) causes a nodular dermatitis in cattle and has high economic consequences in affected areas. Detection of LSDV exposure mostly relies on the humoral immune response, while the cell-mediated immune (CMI) response, an important hallmark of the immune reaction to LSDV, is neglected. We collected samples during 3 weeks post-vaccination of cattle with a Neethling-based live attenuated vaccine (LAV) and during 4 weeks post-LSDV infection under experimental conditions to i) investigate the development of the CMI response, ii) optimize an interferon-gamma release assay (IGRA) by comparing two matrices (whole blood and PBMCs) and different stimuli, and iii) evaluate the usefulness of an IGRA for detection of infection and vaccination. The CMI response to the Neethling LAV was detectable in all animals from 10 days post-vaccination, and importantly, preceded the detection of antibodies. A uniform CMI response to infection was already detected at its plateau level at 7 days post-infection in all animals and also preceded antibody detection. Whole blood and PBMCs allowed efficient IFN-γ secretion, but the IFN-γ response was significantly higher in PBMCs. Heat-inactivated antigen proved to be the stimulus of choice for LSD IGRA, providing increased sensitivity of the test and allowing its performance under BSL2 conditions. Under several conditions, LSDV IGRA showed a specificity of up to 100%. The LSD IGRA could be a powerful immunoassay for early detection of LSD and post-vaccination monitoring, making it worthwhile to explore its diagnostic characteristics in more animals and under field conditions.IMPORTANCEThe immune reaction to lumpy skin disease virus (LSDV) infection or vaccination is currently assessed with serological tests prone to suboptimal sensitivity, long processing time, and the necessity of biosafety level (BSL) 3 laboratories. Furthermore, the delayed or absent seroconversion indicates a need for an alternative immunoassay detecting immune reactions to LSDV exposure applicable in BSL2 settings. Seeing the known importance of cell-mediated immune (CMI) response against poxvirus infections, we evaluated the suitability of the interferon-gamma release assay (IGRA) test for detection of LSDV infection and vaccination. IGRA allowed early detection of the CMI response to LSDV infection (within 7 days) and vaccination (within 10 days) with a Neethling-based live attenuated vaccine, and the CMI response preceded the detection of seroconversion. Whole blood and heat-inactivated antigen increased IGRA sensitivity, making it suitable for application in BSL2 laboratories. This assay overcomes the downsides of currently available immunoassays, and these results encourage its further evaluation.