Submitted to: Porcine Reproductive and Respiratory Syndrome International Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 10/6/2010
Publication Date: 12/3/2010
Citation: Guo, B., Lager, K.M., Yang, H., Faaberg, K.S. 2010. Analysis of Asian PRRSV type 2 strains [abstract]. International PRRS Symposium, Chicago, IL. Paper No. 24. Interpretive Summary:
Technical Abstract: Novel isolates of porcine reproductive and respiratory disease virus (PRRSV) possessing a unique deletion in nonstructural protein 2 with an ORF5 143 RFLP appeared in China in 2006. The isolates were linked to porcine high fever disease (PHFD) and genetically similar to 2007 PHFD PRRSV isolates detected in Vietnam. As part of the USDA response to the emergence of PHFD, we received from the USDA Foreign Animal Disease Diagnostic Laboratory purified RNA from cells infected with the Vietnamese isolate (SRV-07). We also imported an infectious cDNA clone of the Chinese PRRSV JXwn06 strain. Our goals were to examine the ability to detect similar strains and to investigate potential disease consequences to the swine population if such isolates were identified in the U.S. Using SRV-07 purified RNA, a section encompassing ORF4-3' end was amplified for use in determining diagnostic testing sensitivity. The DNA product was cloned, in vitro transcribed, and the RNA forwarded to selected U.S. veterinary diagnostic laboratories for PRRSV quantitative RT-PCR and ORF5 sequencing. All laboratories were able to detect and sequence SRV-07 RNA, and all predicted an ORF5 RFLP of 143. The preparation of an infectious clone of SRV-07 is underway to complete in vitro and in vivo phenotyping. Infectious virus was obtained from the Chinese JXwn06 cDNA clone. Under ABSL3 biocontainment, one pig was intranasally inoculated with 2 ml of 10**6 TCID50/ml rJXwn06 at passage 3. On day 2, a contact pig was placed into the pen. By day 6, the inoculated pig was ill and, on day 9, was moribund and euthanized. Necropsy serum virus titer was 10**7 TCID50/ml. The contact pig only developed mild disease and was euthanized on day 17 (15 days post contact) and PRRSV (10**5.3 TCID50/ml) was also isolated from serum. The results showed the novel Asian PRRSV strains could be detected by U.S. veterinary diagnostic laboratories and that a high dose inoculation with virus rescued from Chinese strain rJXwn06 could cause severe disease. Future work will include completion of our in vitro analyses and additional in vivo challenge studies.