This is our Friday rubric: every week a new Science Page from the Swine Health Monitoring Project. The previous editions of the science page are available on our website.
Key points from this week edition:
Dilute vaccine aerosolization combined with novel environmental sampling techniques allowed for testing of PRRSV aerosol entry into Positive Pressure Filtration (PPF) farm access points.
Under the experimental conditions of this study, positive pressure air speeds >1.85m/s resulted in no aerosol transmission.
Ensuring adequate positive pressure air speed through steps taken to increase access point pressure can further reduce the risk of aerosol PRRSV transmission on PPF farms.
This is our new Friday rubric: every week a new Science Page from the Swine Health Monitoring Project. The previous editions of the science page are available on our website.
Key points from this week edition
We analyzed performance records from 16 sow farms that were vaccinated with PRRS virus and experienced a PRRS virus infection.
Production dropped until the 6th week post-outbreak with a second decline between the 11th and 18th week post-outbreak.
We calculated an average decrease of 1.92 weaned pigs per sow (min=0.51, max=3.72) per year attributable to changes in farrow rate and prewean mortality.
From Dr. Torremorell’s lab at the University of Minnesota, College of Veterinary Medicine
Porcine Reproductive and Respiratory Syndrome virus (PRRSV), Porcine Epidemic Diarrhea virus (PEDV), and High-Path Avian Influenza virus (HPAIV) are transmitted via aerosols.
Air samples taken out of positive farms were successful in isolating HPAIV and PEDV 61% and 69% of the time respectively whereas PRRSV was found 8% of the time.
For all three viruses, higher quantity of genetic material was found when the size of the particle was larger.
Swine and poultryviruses, such as porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV), and highly pathogenic avian influenza virus (HPAIV), are economically important pathogens that can spread via aerosols. The reliability of methods for quantifying particle-associated viruses as well as the sizedistribution of aerosolized particles bearing these viruses under field conditions are not well documented. We compared the performance of 2 size-differentiating airsamplers in disease outbreaks that occurred in swine and poultry facilities. Both airsamplers allowed quantification of particles by size, and measured concentrations of PRRSV, PEDV, and HPAIV stratified by particle size both within and outside swine and poultry facilities. All 3 viruses were detectable in association with aerosolized particles. Proportions of positive sampling events were 69% for PEDV, 61% for HPAIV, and 8% for PRRSV. The highest virus concentrations were found with PEDV, followed by HPAIV and PRRSV. Both air collectors performed equally for the detection of total virus concentration. For all 3 viruses, higher numbers of RNA copies were associated with larger particles; however, a bimodal distribution of particles was observed in the case of PEDV and HPAIV.
This is the question that Drs. Carmen Alonso, Sagar Goyal, Peter Davies, and Montse Torremorell from the College of Veterinary Medicine studied in collaboration with Drs. Bernard Olson and Peter Raynor from the College of Science and Engineering and the School of Public Health respectively, in the following paper published in Aerosol Science and Technology this past month.
In this study, the team form the University of Minnesota compared the capacity of two different air samplers to detect PRRSv and SIV in an experimental setting. The challenge to detect viral aerosol is to find a technique capable of capturing small amount of virus in a large amount of air. This experiment found that the particle size, the media used for collection as well as the extraction technique (passive or active) all had a significant effect on the detection of the viruses.
Abstract: Detection and quantification of dilute viral aerosols, as encountered outside animal housing facilities, requires methods that are able to detect small numbers of viruses in large volumes of air. This study compared the performance of two size-differentiating cascade impactors; an Andersen 8-stage (ACI; 28.3 L/min) and a high volume Tisch (TCI; 1,133 L/min) to assess sampling efficiency for detecting porcine reproductive and respiratory syndrome virus (PRRSV) and influenza A virus (IAV). Samples of particles sorted by aerodynamic diameter were analyzed by quantitative polymerase chain reaction (qPCR) and collection efficiency was assessed by particle size. Collection media (minimum essential medium [MEM] and beef extract [BE]), elution technique (active versus passive), and sampling times (10, 20, and 30 min) were variables assessed for the TCI sampler. Extraction efficiency was 35% higher with BE as compared to that of MEM (p = 0.0007); active extraction technique was 19% more efficient than the passive technique (p = 0.03); time of sampling did not significantly affect the amount of virus recovered. The ACI sampler was more efficient in detecting both viruses from small and medium sized airborne particles (≤3 μm) as compared to the TCI sampler (p < 0.001). The latter sampler, however, was more efficient at IAV detection from large airborne particles (>3 μm) (p = 0.0025) indicating the potential of this sampler in detecting the presence of small amounts of viruses in aerosols under field conditions.
