Concurrent use of reverse transcription-polymerase chain reaction testing of oropharyngeal scrapings and paired serological testing for detection of porcine reproductive and respiratory syndrome virus infection in sows

Abstract

Objective: To investigate the use of porcine reproductive and respiratory syndrome virus (PRRSV) reverse transcription-polymerase chain reaction (RT-PCR) on oropharyngeal scrapings concurrently with paired serological testing for detection of PRRSV infection in sows in commercial herds. Methods: Oropharyngeal scrapings were collected from 191 sows in a 1000-sow, commercial farrow-to-finish herd (Herd A) and from 56 sows in a 900-sow, commercial farrow-to-wean herd (Herd B). Sera were collected from all Herd A sows and 20 Herd B sows. An RT-PCR assay was used to amplify RNA extracted from oropharyngeal scrapings, and a commercial serum ELISA was used to assess PRRSV antibody levels. Results: Oropharyngeal scrapings from 28.3% of Herd A sows and 19.6% of Herd B sows were RT-PCR-positive for PRRSV. Administration of a killed swine influenza vaccine to 80% of Herd A sows 2 weeks before collection of oropharyngeal scrapings did not influence the rate of PRRSV detection. Sera from the 191 Herd A sows and 20 Herd B sows were negative for PRRSV by virus isolation. Virus isolation detected PRRSV in 36.4% of the RT-PCR-positive sows in Herd B. With RT-PCR results as an indicator of the true PRRSV status of the sow, paired ELISA testing had a sensitivity of 70.4% and a specificity of 49.6%. Implications: Oropharyngeal scrapings were RT-PCR-positive for PRRSV RNA in aviremic, clinically normal sows and in some sows with PRRSV ELISA sample: positive ratios <0.4. The diagnostic parameters of paired serological testing will likely preclude the use of this method for detecting PRRSV RT-PCR-positive sows.