Comparison of sample materials for the detection of infection with porcine reproductive and respiratory syndrome virus

Abstract

In breeding farms with a high health status, pigs are frequently sampled using invasive methods (i. e. blood sampling). The aim of the present study was to evaluate less invasive methods concerning their suitability for an early detection of the infection with the porcine reproductive and respiratory syndrome virus (PRRSV). Blood and saliva swabs, chewing rope derived oral fluids and serum samples were used for PRRSV-1 and PRRSV-2 detection via PCR. 19 gilts were repeatedly sampled following intramuscular or intranasal vaccination with live-attenuated vaccines containing PRRSV-1 or -2. Swabs were either moistened with saliva from the mouth mucosa or with blood from the ear veins following superficial needle puncture. Serum samples were taken via puncture of the V. jugularis externa. Chewing ropes served for a means of oral fluid sampling and were kept hanging in the barn at the pigs' head height for 30 minutes. All animals were negative for PRRSV at the time of vaccination (sampling point 0). In serum samples, the first virus detection was achieved 12 hours following vaccination (p. vacc.). From day 4 p. vacc. on all animals were viremic and from day 10 p. vacc. on the percentage of positive animals decreased. The first detection of PRRSV in GenoTube® blood swabs was possible 36 hours p. vacc. Examination of the eSwab® blood swab resulted in only one positive finding within the entire testing period. In the saliva samples, first detection of PRRSV was possible on day 5 p. vacc. This study demonstrates that serum samples taken from the V. jugularis externa may be considered as the gold standard for diagnostic of PRRSV viremia. Detection rates in serum were higher than in the alternative sample types. However, since sample collection procedures and processing of the alternative sample materials offer clear advantages with regard to welfare, practical handling and logistics, further attempts are warranted in order to improve these methods. Based on the presented results, the described method using eSwab® blood sampling does not represent a satisfactory alternative approach for the detection of early PRRSV infection. Future application of this method warrants further improvement of its diagnostic efficacy.