Development of a simple on-site diagnostic test to detect PRRSV acute infection in boar studs

Because PRRSV can be transmitted through artificial insemination with semen from infected animals, boar studs are constantly being monitored for the presence of PRRSV. Current monitoring protocols for PRRSV in most boar studs in North America consist of routine sampling of boars and testing of these samples by RT-PCR in diagnostic laboratories. Considering the large number of samples being run in a large boar stud, and the importance of a quick turnaround time of results, it would be advantageous to run the diagnostic test on site. Unfortunately, RT-PCR requires sophisticated equipment, specialized labor and cannot be implemented successfully outside a specialized laboratory. The objective of this study was to investigate the feasibility of using a new diagnostic test (RT-LAMP) for the detection of PRRSV. RT-LAMP is a recently described diagnostic test reported to be simple, inexpensive, fast and accurate that can be performed in a simple heat block. The RT-LAMP was designed to detect both the North American and European strains of PRRSV. The RT-LAMP was able to detect seven different PRRSV isolates. However, it failed to detect small amounts of virus (the limit of detection ranged between 10² and 10⁴ TCID₅₀/ml). Further evaluation included validation of the RT-LAMP using samples from animals of known infection status. The ability of RT-LAMP to detect PRRSV in serum from acutely infected animals (sensitivity) was evaluated with 114 serum samples from 18 experimentally inoculated boars. Forty-nine of these samples tested positive by RT-LAMP, while 94 were positive by RT-PCR. Furthermore, the ability of the test to correctly identify negative samples (specificity), evaluated with 100 known negative sera, was estimated as 99%. The feasibility of RT-LAMP to detect PRRSV was demonstrated in this study. The RT-LAMP reaction could be performed in just 1 hour with a simple and inexpensive heat block with good specificity. However, the sensitivity was lower than that of RT-PCR. Nevertheless, there is potential for this technique to be applied in situations where RT-PCR is too expensive or too sophisticated to be implemented.