Joseph R. Hermann

Antigen-Specific B-Cell Responses to Porcine Reproductive and Respiratory Syndrome Virus Infection

ABSTRACT 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 Peyers 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.

Optimization of a Sampling System for Recovery and Detection of Airborne Porcine Reproductive and Respiratory Syndrome Virus and Swine Influenza Virus

ABSTRACT 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.

A method to provide improved dose–response estimates for airborne pathogens in animals: An example using porcine reproductive and respiratory syndrome virus

Abstract This paper describes a method to provide improved probability estimates that exposure to a specific dose of an airborne infectious pathogen will result in animal infection. Individual animals were exposed to a specific dose of airborne pathogen. Following exposure, animals were individually housed and monitored for evidence of infection. The detection of specific antibodies and/or the pathogen in diagnostic specimens was evidence that the exposure dose resulted in infection. If replicated over a range of doses, the results can be used to derive a dose–response curve for a variety of animal species and infectious pathogens. This information is useful in estimating the likelihood of infection associated with exposure to airborne infectious microorganisms. Applications include predicting the risk of transmission associated with exposure to airborne pathogens, modeling the transmission of airborne pathogens, and determining requirements for effective exposure doses for vaccines delivered in aerosols.

Stability of Porcine reproductive and respiratory syndrome virus at ambient temperatures.

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 Ingelvac® PRRS ATP vaccine virus) in cell culture medium (pH 7.5) were held at 1 of 4 temperatures (4, 10, 20, and 30°C) 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 [T 1/2]). Statistical analysis found that temperature, but not virus isolate, had a significant effect on T 1/2, and a single nonlinear regression model was derived to predict T 1/2 for temperatures between 0 and 50°C: T 1/2 = 243.54 e(-0.109*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.