-The objective of this experiment was to describe the stability of airborne infectious porcine reproductive and respiratory syndrome virus (PRRSV) as a function of temperature and relative humidity. A cloud of infectious PRRSV was aerosolized using 24-jet Collison nebulizer into a dynamic aerosol toroid (DAT) maintained at a specific temperature and relative humidity. The PRRSV cloud within the DAT was sampled repeatedly over time using SKC BioSampler impingers and the total viral RNA (RT-PCR) and concentration of infectious PRRSV (TCID 50 ) in the air samples was determined. As measured by quantitative RT-PCR, PRRSV RNA was stable under the conditions evaluated in this study. Thus, a comparison of viral RNA and Rhodamine B dye, a physical tracer, found no significant difference in the slopes of the lines. Titers of infectious virus were plotted by time and the half-life (T 1/2) of infectious PRRSV was calculated using linear regression analysis. An analysis of the results showed that aerosolized PRRSV was more stable at lower temperatures and/or lower relative humidity, but temperature had a greater effect on the T 1/2 of PRRSV than relative humidity. Based on these results, an equation was derived to predict the T 1/2 of infectious airborne PRRSV for any combination of environmental temperature and relative humidity.aerosol / virus stability / PRRSV / relative humidity / temperature
The objective of this research was to optimize sampling parameters for increased recovery and detection of airborne porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza virus (SIV). Collection media containing antifoams, activated carbons, protectants, and ethylene glycol were evaluated for direct effects on factors impacting the detection of PRRSV and SIV, including virus infectivity, viability of continuous cell lines used for the isolation of these viruses, and performance of reverse transcriptase PCR assays. The results showed that specific compounds influenced the likelihood of detecting PRRSV and SIV in collection medium. A subsequent study evaluated the effects of collection medium, impinger model, and sampling time on the recovery of aerosolized PRRSV using a method for making direct comparisons of up to six treatments simultaneously. The results demonstrated that various components in air-sampling systems, including collection medium, impinger model, and sampling time, independently influenced the recovery and detection of PRRSV and/or SIV. Interestingly, it was demonstrated that a 20% solution of ethylene glycol collected the greatest quantity of aerosolized PRRSV, which suggests the possibility of sampling at temperatures below freezing. Based on the results of these experiments, it is recommended that air-sampling systems be optimized for the target pathogen(s) and that recovery/detection results should be interpreted in the context of the actual performance of the system. Airborne pathogens are detected by recovering the target microorganism in a collection medium (liquid, semisolid, or solid substrate) and then assaying the substrate for the presence of the target pathogen by using an appropriate microbiological assay. Various air-sampling devices are available, but "impingers" are generally used to collect airborne viruses. Impingers direct a converged stream of environmental air onto a liquid collection medium to recover airborne viral particles in the liquid phase of the collection system (1,11,12,14,16,17). Impingers are generally considered more effective than filters, bubblers, or impactors for capturing airborne viruses (18,19,20).A number of variables are known to affect impinger collection efficiency. These include impinger design (5, 13, 24), sampling time (28), and the composition of collection medium (31). In addition, specific compounds are sometimes added to impinger collection medium to preserve virus infectivity during the collection process (37,38,40).This research focused on specific aspects of optimizing the collection and detection of aerosolized porcine reproductive and respiratory syndrome virus (PRRSV) and swine influenza virus (SIV) in air-sampling systems. The first study (experiment 1) focused on virus detection. Compounds added to collection media to enhance collection efficiency (i.e., antifoams, bovine serum albumin, gelatin, mucin, activated carbon, and ethylene glycol) were evaluated for direct effects on virus infectivity, on the viability ...
Porcine reproductive and respiratory syndrome virus (PRRSV) causes an acute, viremic infection of 4 to 6 weeks, followed by a persistent infection lasting for several months. We characterized antibody and B-cell responses to viral proteins in acute and persistent infection to better understand the immunological basis of the prolonged infection. The humoral immune response to PRRSV was robust overall and varied among individual viral proteins, with the important exception of a delayed and relatively weak response to envelope glycoprotein 5 (GP5). Memory B cells were in secondary lymphoid organs, not in bone marrow or Peyer's patches, in contrast to the case for many mammalian species. Potent anti-PRRSV memory responses were elicited to recall antigen in vitro, even though a second infection did not increase the B-cell response in vivo, suggesting that productive reinfection does not occur in vivo. Antibody titers to several viral proteins decline over time, even though abundant antigen is known to be present in lymphoid tissues, possibly indicating ineffective antigen presentation. The appearance of antibodies to GP5 is delayed relative to the resolution of viremia, suggesting that anti-GP5 antibodies are not crucial for resolving viremia. Lastly, viral infection had no immunosuppressive effect on the humoral response to a second, unrelated antigen. Taking these data together, the active effector and memory B-cell responses to PRRSV are robust, and over time the humoral immune response to PRRSV is effective. However, the delayed response against GP5 early in infection may contribute to the prolonged acute infection and the establishment of persistence.
Abstract. The stability of Porcine reproductive and respiratory syndrome virus (PRRSV) was evaluated for temperatures appropriate to laboratory and field settings. Four North American (type 2) isolates (ATCC VR-2332, JA-142, MN-184, and IngelvacH PRRS ATP vaccine virus) in cell culture medium (pH 7.5) were held at 1 of 4 temperatures (4, 10, 20, and 30uC) and sampled over time. Samples were tested for infectious virus and total PRRSV RNA using median tissue culture infectious dose and quantitative reverse transcription polymerase chain reaction, respectively. The rate of loss of infectious virus was expressed in terms of the time required for virus concentration to decline by one half (i.e., half-life [TK]). Statistical analysis found that temperature, but not virus isolate, had a significant effect on TK, and a single nonlinear regression model was derived to predict TK for temperatures between 0 and 50uC: TK 5 243.54 e (20.109*TEMP) . In contrast to changes over time in the concentration of infectious virus, no change in the concentration of quantitative reverse transcription polymerase chain reaction-detectable PRRSV was detected at any temperature and contact time. This information will be of interest to persons working in laboratory or field situations in which the control of PRRSV is important.
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