Comparison of an in-house and a commercial ELISAs for antibody detection against highly pathogenic porcine reproductive and respiratory syndrome virus

Highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRS) caused economic losses in swine industry. Several ELISAs have been developed for rapid diagnosis and assisting in control of the disease. The aim of this study was to determine an efficiency of a newly developed in-house ELISA for detection of antibodies against HP-PRRS virus (HP-PRRSV) in serum.

Nursery pigs from a PRRSV-negative herd were randomly divided into 3 groups and housed in separate rooms. Group 1 (n=9) was a negative control. Group 2 (n=15) included pigs vaccinated with PRRS vaccine (FosteraTM, Zoetis) at day 0 and experimentally infected with HP-PRRSV at day 28. Pigs in group 3 (n=15) were experimentally infected with HP-PRRSV at day 28. Sera were collected at day 0, 14, 28, 35 and 42. Real-time RT-PCR was used to detect the presence of HP-PRRSV RNA in serum. All sera were analysed with an in-house ELISA and a commercial ELISA (IDEXX PRRS X3 Ab test). Sera of group 2 at day 14, 28, 35 and 42 and sera of group 3 at day 35 and 42 were used to estimate sensitivity of the tests. The rest of the sera were used to evaluate specificity of the tests. Efficiencies of the tests were analysed by area under curve (AUC). Kappa coefficient and Pearson correlation coefficient between S/P ratios of sera of the two tests were calculated.

Based on real-time RT-PCR, all pigs in group 1 stayed negative until the end of the study as well as all pigs in group 2 before vaccination and all pigs in group 3 before the challenge. The PRRSV were presented in 2 pigs in group 2 after vaccination whereas the viruses were detected in all pigs from group 2 and 3 after the challenge. Both ELISAs were able to detect seroconversion at 1 week after HP-PRRSV inoculation in either group 2 or group 3. The mean S/P ratio of group 2 from in-house ELISA was higher than that of a commercial ELISA after HP-PRRSV challenge (Fig 1). However, higher number of positive pigs was identified by the commercial ELISA after vaccination. Sensitivity and specificity of the in-house ELISA were 85.3% and 98.4%, respectively. Both ELISAs showed a good agreement based on kappa coefficient (k=0.8) and Pearson correlation coefficient (r=0.8). The AUC of the in-house ELISA was 0.94.

The newly developed in-house ELISA is reliable and can be used for antibody detection against PRRSV-vaccinated and HP-PRRSV-infected pigs. A sharp increase in S/P ratio after HP-PRRSV infection is a useful indicator for PRRS monitoring in a field situation.

Disclosure of Interest: None Declared.