Preliminary validation of a single-spot version of a solid-phase competition ELISA for the detection of southern African territories foot-and-mouth disease serotype exposure in goats

The objective of this study was to perform a preliminary validation of a solid-phase competition ELISA (SPCE) in goats exposed to foot-and-mouth disease virus (FMDV) southern African territories (SAT) serotypes through vaccination or experimental infection. Thirty-nine goats were vaccinated with a FMDV vaccine and 37 subsequently challenged with a SAT1 virus serotype. Blood was collected every 7 days until termination at 14 days post-challenge. Single-spot SAT1 virus serotype SPCE (ss-SPCE) was performed in duplicate at two time points and a half-titration version was performed after a variable time of long-term storage. Coefficient of variation (CV) was calculated and accuracy of the ss-SPCE was estimated relative to a half-titration SPCE log10 titer of 1.6 using mixed-effect logistic regression. Additionally, sensitivity and specificity were estimated based on serological results 14-days post-challenge and at study enrolment, respectively. Three hundred and forty-two serum samples were tested in duplicate on two non-consecutive days. The median (interquartile range (IQR)) CV for the ss-SPCE for SAT1 was 2.1% (0.5, 14.3%) and 2.5% (0.6, 12.8%) for the two testing days, respectively. Median (IQR) inter-assay (different day) CV was 10.6% (2.5, 42.5%). Specificity and sensitivity of the ss-SPCE relative to the log10 titer using a 70% percentage inhibition positive threshold were 83.4% (95% confidence interval, 77.7–87.9) and 95.8% (90.7–98.2), respectively. Specificity was estimated as 100% (92.6, 100) and sensitivity as 97.3% (87.4, 99.9) when only considering serum tested at the beginning and end of the study, respectively. The SAT1 ss-SPCE is repeatable and accurate for determining FMDV serological status in goats.