Transmission of porcine reproductive and respiratory syndrome virus in domestic pigs via oral ingestion of feed material

OBJECTIVE The purpose of this case study was to describe the transmission of porcine reproductive and respiratory syndrome virus (PRRSV) under field and experimental conditions via the consumption of PRRSV-positive swine feed. ANIMALS 1 domestic swine breeding herd and 20 laboratory -maintained experimental domestic pigs. CLINICAL PRESENTATION, PROGRESSION, AND PROCEDURES A 2,500 -sow PRRSV-naive biosecure breeding herd became infected during the autumn months. It experienced feed outage involving a specific bin on October 23 (day 0), with the bin refilled on October 24 (day 1). From tober 28 to 30 (days 5 to 7), signs of anorexia and hyperemia were observed in 30 gestating sows after consuming feed from this bin. On November 1 (day 9), blood samples from 10 affected sows were PRRSV positive by reverse transcriptase PCR. In contrast, sows in the same room that had consumed feed from other bins were clinically mal and PRRSV negative. To investigate whether the feed delivery introduced PRRSV to the herd, on November (day 10) 4 samples of feed material from the interior walls of the index bin were collected and tested by reverse transcriptase PCR. TREATMENT AND OUTCOME All 4 samples were positive for PRRSV RNA with cycle threshold values ranging from 26 to 29. Nucleic acid quencing indicated that the open reading frame 5 region of the PRRSV in feed samples was 100% homologous PRRSV from index cases. To assess viability of the virus, PRRSV-naive pigs were allowed to consume the feed bin samples and became infected with PRRSV based on viral RNA in oral fluid samples, clinical signs, postmortem lesions. CLINICAL RELEVANCE These results suggest that feed was a likely source of PRRSV introduction to the herd. This is the first report PRRSV transmission through feed.