Date of Award
Doctor of Philosophy
Veterinary Microbiology and Preventive Medicine
Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped RNA virus in the family Arteriviridae within the order Nidovirales (Cavanagh, 1997).;The objective of the first study was to optimize sampling parameters for increased recovery and detection of airborne 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 polymerase chain reaction (RT-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. Based on the results of these experiments, the air sampling parameters were optimized for sampling i.e. recovery/detection of PRRSV and implemented throughout the remaining experiments.;The objective the second study was to estimate the analytical sensitivity (detection threshold) of each of four air samplers (AGI-30, AGI-4, SKC BioSampler, and Midwest Micro-Tek sampler) for PRRSV and SIV. In a 5 minute sampling period under controlled conditions, the analytical sensitivity of the AGI-30, AGI-4, SKC BioSamplerRTM, and Micro-Tek samplers for PRRSV was calculated at 1 x 101.1, 1 x 101.3, 1 x 101.1, and 1 x 101.2 TCID50 equivalents and 1 x 10 1.4, 1 x 101.1, 1 x 101.6, for SIV. Despite marked differences in sampler design, no statistically significant difference in analytical sensitivity was detected between samplers for collection of artificially produced aerosols containing cell culture propagated PRRSV or SIV. Detection thresholds obtained from this experiment were used for reference in excretion studies.;The objective of the third study was to characterize the excretion of these pathogens in respirations from acutely infected pigs. Pigs were inoculated under experimental conditions with one pathogen. Samples were collected from the upper respiratory tract and respiratory exhalations. All pathogens were detected in the upper respiratory tracts of inoculated pigs, but only M. hyopneumoniae and B. bronchiseptica were detected in expired air from individually-sampled, acutely-infected pigs. These findings suggested either that acutely infected pigs did not aerosolize PRRSV, PCV-2, SIV, or PRCV, or that the quantity of virus excreted was below the analytical sensitivity (detection threshold) of current sampling and/or assay systems at the individual pig level.;The objective of the forth study was to describe the stability of airborne infectious PRRSV as a function of temperature and relative humidity. A cloud of infectious PRRSV was aerosolized using a 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 BioSamplerRTM impingers and the total viral RNA (RT-PCR) and concentration of infectious PRRSV (TCID50) 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 (T1/2) 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 T1/2 of PRRSV than relative humidity. Based on these results, an equation was derived to predict the T1/2 of infectious airborne PRRSV for any combination of environmental temperature and relative humidity.;The objective of the fifth study was to describe and validate a method that provides improved estimates of the probability that exposure to a specific dose of an airborne infectious pathogen will result in infection in animals. To validate the proposed method, 7 replicates of 10 pigs per replicate were conducted. Pigs were exposed to specific doses of airborne PRRSV. Following exposure, animals are individually housed and monitored for evidence of infection. The relationship describing the probability of infection after exposure was modeled on the proportions of pigs that became infected by exposure to specific doses. A dose response curve was derived using logistical models. Based on this methodology dose-response curves may be derived for a number of animal host and infectious pathogens. (Abstract shortened by UMI.)
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Joseph Ralph Hermann
Hermann, Joseph Ralph, "Quantitative studies on airborne transmission of porcine reproductive and respiratory syndrome virus" (2008). Retrospective Theses and Dissertations. 15641.