Bioassay of PEDv Aerosol Samples

September 18, 2013 — 

Air samples collected from 60 feet away from a barn up to 10 miles away were tested by PCR. Ten samples were positive (Ct 36-38) and were tested by bioassay to determine if we could detect any live virus. We included 2 confirmed positive control samples (Ct 16 & 38) and a negative control sample. Fifteen 10-day-old pigs were allocated to 13 isolation rooms and inoculated. All pigs were euthanized 48 hours after inoculation and their tissues were tested for PEDv PCR. The low Ct-value positive control was the only piglet to demonstrate clinical signs and a positive PCR test. The bioassay of the 10 PCR positive aerosol samples was negative.

Since the dilute positive control sample (similar Ct-value to air samples) and the air samples were not infective, this study may indicate any or all of the following:

• Dilution of the virus to that point may prevent infectivity even in live samples
• Dilution of the virus to that point may need more time for replication to be detected (previous bioassay study only showed dilutions at Ct ≤30 successfully infecting in this time frame)
• There was no live virus in the PCR positive air samples

Source: Swine Health Monitoring Project, UMN courtesy of D Goede, R Robbins, L Dufresne, M Engle, RB Morrison