As stated in the contract, we require an industry summary of the project, suitable for immediate public release by the Board.  The purpose of the industry summary is to provide producers with a quick reference to research results supported by Checkoff dollars.  The content should include the following:  an explanation of the objectives, descriptive narrative of how research was conducted, a discussion of the research findings sufficient to give a thorough understanding of the results, and explain what these findings mean to the industry.  This summary is to be written for non-technical audiences.  Please include your contact information.
 The prevalence of PRRSV infection in swine herds is high. Current strategies to control the spread and impact of PRRSV infection once it enters a herd have largely been proven inadequate. Development of new vaccines or improvement of the current vaccines is needed. The typical features of the immune responses in PRRSV-infected pigs are delayed inception and low level of neutralizing antibodies as well as weak cell-mediated immunity. One of the possible reasons is that PRRSV interferes with the innate immunity, including downregulation of type I interferons (IFNs) in infected pigs. Type I IFNs are critical to the innate immunity against virus infections and play important roles in activation of the adaptive immunity. It is fortunate that we discovered an IFN-inducible PRRSV strain, A2MC2, which provides a good opportunity to develop an improved vaccine against PRRS. The virus was serially passaged in cultured cells to passage 90 (A2MC2-P90) in laboratory. The high passage virus is still able to induce IFNs. The objectives for this project are to assess the virulence and efficiency of A2MC2-P90 in elicitation of the host immune response and to construct A2MC2-P90 infectious clone. Nucleic acid sequencing of the A2MC2-P90 genome was conducted. Sequence analysis showed that the A2MC2-P90 has genomic nucleic acid identity of 99.8% to the wild type but has a deletion of 543 nucleotides. The cDNA of the full-length genome of A2MC2-P90 was amplified and assembled for construction of an infectious clone. The establishment of this clone will be useful for further studying the biology of this virus and development of an improved vaccine against PRRS. The A2MC2-P90 virus  was tested in young pigs along with the wild type A2MC2 and Ingelvac PRRS® MLV strain. Inoculation of three-week-old piglets showed that A2MC2-P90 is avirulent and elicits the host immune response. Compared with the Ingelvac PRRS® MLV strain, A2MC2-P90 elicits higher virus neutralizing antibodies. The avirulent IFN-inducing A2MC2-P90 should be useful for development of an improved PRRSV vaccine. Application of such a vaccine will yield significant economic benefits to the swine industry by preventing PRRS.
For more information, contact Dr. Zhang at the University of Maryland: [email protected].