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United States Department of Agriculture

Agricultural Research Service

Title: Postweaning multisystemic wasting syndrome produced in gnotobiotic pigs following exposure to various amounts of porcine circovirus type 2a or type 2b

Authors
item Gauger, Phillip
item LAGER, KELLY
item VINCENT, AMY
item Opriessnig, T - IOWA STATE UNIVERSITY
item Kehrli Jr, Marcus
item CHEUNG, ANDREW

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 23, 2011
Publication Date: December 15, 2011
Citation: Gauger, P.C., Lager, K.M., Vincent, A.L., Opriessnig, T., Kehrli, Jr., M.E., Cheung, A.K. 2011. Postweaning multisystemic wasting syndrome produced in gnotobiotic pigs following exposure to various amounts of porcine circovirus type 2a or type 2b. Veterinary Microbiology. 153(3-4):229-239.

Interpretive Summary: About 10 years ago porcine circovirus type 2 (PCV2) was being recognized as an emerging swine pathogen. PCV2 plays a significant role in a group of swine diseases that are collectively known as PCV2 associated disease (PCVAD). In late 2005, a postweaning, high mortality syndrome spread rapidly through finishing barns in swine dense areas of the United States. Diagnostic investigations consistently isolated PCV2 from diseased tissues. Subsequent genetic analysis revealed the infectious agent was PCV2-group 1 (PCV2-Gp1). Prior to late 2004, only PCV2-Gp2 (but not PCV2-Gp1) had been reported in North America. In this communication, we demonstrate an acute high mortality disease in germ-free pigs using infectious viruses generated from a DNA clone constructed from a PCV2-Gp1 isolate identified in the 2005 outbreak. Clinical signs exhibited by diseased pigs mimicked the epidemic of 2005 suggesting this PCV2 Gp1 strain played a role in the field cases indicating this syndrome might be included under the PCVAD diagnosis. Demonstrating the linkage between the newly identified PCV2 strain and the field cases supports the assumption in the field that such a linkage exists. Moreover, this linkage supports the use of newly available PCV2 vaccines.

Technical Abstract: In late 2005, a postweaning, high mortality syndrome spread rapidly through fattening barns in swine dense areas of the United States. Diagnostic investigations consistently isolated porcine circovirus type 2 (PCV2) from diseased tissues. Subsequent genetic analysis revealed the infectious agent was PCV2-group 1 (PCV2-Gp1). Prior to late 2004, only PCV2-Gp2 (but not PCV2-Gp1) had been reported in North America. In this communication, we demonstrate an acute high mortality disease in germ-free pigs using infectious viruses generated from a DNA clone constructed from a PCV2-Gp1 isolate identified in the 2005 outbreak. Clinical signs exhibited by diseased pigs include anorexia, dyspnea and listlessness. Mortality was typically seen within 12 hours of onset of dyspnea. The most striking microscopic lesions in affected animals were severe hepatic necrosis, severe depletion of germinal centers in lymph nodes and abundant viral antigens associated with lesions in affected tissues. Clinical effects and lesions observed in this study were comparable to those observed in experiments with a PCV2-Gp2 isolate in which germ-free pigs received immune-stimulation or co-infection with porcine parvovirus. The experimental animals were free of detectable porcine parvovirus, bovine viral diarrhea virus, porcine reproductive and respiratory syndrome virus, and aerobic and anaerobic bacteria throughout the study. Thus, this PCV2-Gp1 isolate alone was capable of inducing a high mortality syndrome without any recognized infectious co-factor. In a separate study with 4 pigs per challenge group, PCV2-Gp1 isolate was more pathogenic when compared to a PCV2-Gp2 isolate recovered from the same case during the 2005 outbreak.

Last Modified: 7/25/2014
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