Validation of Senecavalley virus A VP2 (SVA VP2) ELISA offered at the VDL

February 9, 2017

An indirect ELISA assay was developed to specifically identify serum antibodies to Senecavalley virus A (SVA) by Dr. Michael Murtaugh’s Laboratory. The plates were coated with antigen prepared by purification of E. coli cloned and expressed viral protein 2 (VP2). To validate, positive serum samples were obtained from 34 sows clinically diagnosed with vesicular lesions and bled periodically over a 60-day period starting at the first observation of clinical signs (sampling at day 0, 4, 11,18, 25, 39, and 60;  n=205). Negative serum samples (n=116) were obtained from sows and finishing pigs from various farms with no prior evidence of vesicular disease. These animals were assumed to be SVA antibody-negative.

 ROC analysis was performed using 116 negative samples and 205 positive samples. At a positive/negative sample cut-off value of OD=0.6, the area under the curve to differentiate positive from negative was 0.9622 with a p value <0.0001. Test sensitivity was 94.2% and specificity was 89.7%.

Comparison of negative samples and positive samples from the infection time course showed that ELISA and IFA were correlated (n=231, p<0.0001). The IFA has a specificity of 100% and a sensitivity of 90.3%. Agreement on negative samples was 89% and agreement from 4 to 60 days after appearance of clinical signs varied from 73-100%. However, on the day that clinical signs were first observed (coded as study day 0), test agreement was 40%, which was due to samples testing ELISA positive, but IFA negative or suspect. In cases of disagreement, ELISA was usually positive while IFA was negative or suspect. Three percent of total samples were ELISA negative, but IFA positive (days 11, 18, and 60). Cross-reactivity against other viruses was low and was confirmed as negative after examination by a secondary assay. The SVA VP2 ELISA is a rapid, sensitive, and specific test to identify if a herd is infected with SVA.

Cheryl Dvorak, Suzanne Stone, Fabio Vannucci, Devi Patnayak and Michael Murtaugh