| Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped, positive stranded RNA virus belonging to the Arteriviridae family and has emerged as the most economically important swine disease in the mid 1990's.; The overall objective of our studies was to characterize the in vivo pathogenesis and virulence of both type 1 and type 2 PRRSV strains. In all three experimental chapters, experiments were designed to assess the clinical condition of animals as well as measure changes in viral load, antibody, and virus neutralization activity. Our first objective, outlined in the second chapter, was to perform a detailed pathological analysis of Type 1 isolates now circulating in the United States. More specifically, our aim was to evaluate neutralizing properties of sera from pigs experimentally infected with representative U.S. Type 1 isolates and to assess serological cross protection among different isolates. Our second objective, outlined in the third and forth chapters, was to examine the potential of PRRSV to persist in the host by developing a diagnostic, in situ hybridization tool to identify cell types within various tissues that support low-level viral replication. In addition, we were able to use the data to build a model of PRRSV replication throughout the various stages of disease. The following three studies describe the rationale, experimental design, results and future direction of the research.; The goal of the first study was to evaluate the virus neutralizing and pathogenic properties of selected Type 1 isolates based upon their genetic differences, geographic isolation and clinical symptoms. We hypothesize that understanding differences in neutralization titers among PRRSV strains will lead to developing vaccines with a wide cross protection among other strains. Forty landrace-yorkshire pigs aged 4-6 weeks, were divided into 5 groups and inoculated with one of four different European-like isolates; the fifth group serves as a negative control. Blood samples and tissues were collected and characterized for viral load, antibody response and persistence. Clinical signs and pathology were variable among groups and all animals seroconverted within two weeks. Neutralizing antibody response among homologous challenge isolates reached a titer of at least 1:16 among all isolates and peaked upwards of 1:128 by 56 dpi. This study was the first controlled study to report on the relative virulence, persistent potential and pathogenesis of diverse U.S. Type 1 PRRSV isolates. (Abstract shortened by UMI.)... |
