Validation of an ELISA kit for detection of antibodies against ASF virus in blood or spleen of domestic pigs and wild boars

The causal agent of African swine fever (ASF) is a DNA virus belonging to Asfaviridae family which affects both wild boar Sus scrofa and domestic pig Sus scrofa domestica. Special features of the course of (ASF and its forms should be considered for the effective use of various ASF diagnostic methods aimed at the pathogen or specific antibody identification. ASF diagnosis in the wild boar is of special importance. The wild boar susceptibility to ASF virus is well known, and the disease has been repeatedly reproduced in experiments and detected in European wild boars in natural conditions. It is not unfrequently that when shooting wild boars, only organ samples are delivered to laboratories, so we decided to estimate the diagnostic value of the antibodies detected in tissues and evaluate an earlier developed test system for its efficacy when used for the assay. This report represents the results of validation of an indirect ELISA (a commercial kit «VNIIVViM ASF-ELISA Ab/Ag») ASF virus specific antibody detection in blood serum and spleen tissue extracts. For comparison, an indirect immunofluorescence assay (indirect IFA) was used. To estimate the obtained results, ROC analysis was applied. Examination of positive ( n = 66) and negative ( n = 410) porcine blood serum samples using indirect ELISA showed high sensitivity and specificity of the method with reference to IFA. Among the 476 serum samples examined in indirect ELISA, only 8 sera (1.6 %) were within the positive/negative cutoff area. The highest sensitivity (100 %) and specificity (99.27 %) for indirect ELISA when examining both domestic pig and wild boar blood sera were determined at a cutoff value of 0.264. The samples of spleen extracts to be used for the study were collected from clinically healthy wild boars in ASF-affected Smolensk region in 2013 to 2014. In view of an acute form of the disease, we can suspect that the animals exhibiting positive reaction were in a latency period of the pathogeny. When examining the positive ( n = 59) and negative (n = 678) spleen extracts, we also determined high sensitivity and specificity levels of indirect ELISA with reference to indirect IFA. Among the samples examined ( n = 737), 10 (1.3 %) samples of spleen extracts were within the positive/negative cutoff area. The highest sensitivity (100 %) and specificity (98.82 %) were observed at a cutoff value of 0.284. Thus, we confirmed the assay to be effective for porcine blood sera with 100 % sensitivity (94.6 to 100 %) and 99.27 % specificity (97.90 to 99.80 %) and for spleen extracts with 100 % sensitivity (93.90 to 100 %) and 98.82 % specificity (97.70 to 99.50 %).