Submitted to: World Association of Veterinary Laboratory Diagnosticians
Publication Type: Proceedings
Publication Acceptance Date: 8/10/2007
Publication Date: 11/11/2007
Citation: Cheung, A.K., Lager, K.M., Gauger, P.C., Vincent, A.L., Opriessnig, T., Kehrli, Jr., M.E. 2007. Reproduction of PMWS of high mortality with a porcine circovirus type 2-group 1 isolate. In: Proceedings of the 13th International World Association of Veterinary Laboratory Diagnosticians Symposium, November 11-14, 2007, Melbourne, Australia. p. 213.
Technical Abstract: Introduction In late 2005, sporadic cases of an acute onset of high mortality disease were observed in growing pigs among USA swine herds. PCV2-group 1 (Gp1) virus was consistently detected among the affected animals. Phylogenetic analysis showed that the PCV2 isolates from the United States until late 2005 belonged to PCV2-group 2 (Gp2) (1,2). The objective of this study was to examine the pathogenic capability of Gp1 and Gp2 viruses in germ-free pigs. Material & methods Virus. Infectious viruses were generated from bacterial plasmids containing Gp1 and Gp2 nucleotide sequences. The viral genomes were excised from the bacterial plasmids after delivered into PK15 cells via lipofectamine transfection. Infectious viruses were recovered from the transfection cell cultures after 1 week. Experimental design. Pigs were derived under sterile conditions and maintained germ-free in isolators. The pigs were fed a sterile milk diet and at 12 days of age (day 0 of the experiment) were given an intranasal inoculation of either Gp1 virus, Gp2 virus or cell culture medium. The pigs were monitored for clinical signs with a plan of euthanizing all pigs 41 days-post-inoculation. Results Mortality of the infected pigs in 2 independent experiments with Gp1 was 50% (6/12 pigs) and 100% (4/4 pigs), respectively. In one experiment, Gp1 (4/4 pigs) was found to be more virulent than Gp2 (1/4 pigs). The most significant lesions observed in the diseased pigs were depletion and replacement of lymphoid follicles by macrophages, and severe vacuolar degeneration and necrosis of hepatocytes with multifocal areas of hemorrhagex. Abundant PCV2 antigen was detected in tissues of affected pigs. In our analysis, no other microorganisms were detected in the animals throughout the experiment. Since the viruses used in this study were derived from cloned DNA, we presume the clinical effects were attributed to the respective virus isolate. Discussions & conclusions Here, we report reproduction of PMWS of high mortality in germ-free pigs by a Gp1 virus alone and without immune stimulation or co-infection with another infectious agent (3,4). In this study, the Gp1 isolate was more pathogenic when compared to the Gp2 isolate identified in the same 2005 United States outbreak. In our analysis, no other microorganisms were detected in the affected pigs. References 1. Olvera A, Cortey M, Segales J. (2007) Molecular evolution of porcine circovirus type 2 genomes: phylogeny and clonality. Virology 357: 175-185. 2. Cheung A, Lager K, Kohutyuk O, Vincent A, Henry S, Baker R, Rowland R, and Dunham A. (2007) Detection of two porcine circovirus type 2 genotypic groups in United States swine herds. Arch Virol 152:1035-1044 3. Ellis J, Krakowka S, Lairmore M, Haines D, Bratanich A, Clark E, Allan G, Konoby C, Hassard L, Meehan B, Martin K, Harding J, Kennedy S, McNeilly F. (1999) Reproduction of lesions of postweaning multisystemic wasting syndrome in gnotobiotic piglets. J Vet Diagn Invest 11:3-14. 4. Krakowka S, Eillis J, Meehan B, Kennedy S, McNeilly F, Allan G. (2000) Viral wasting syndrome of swine: experimental reproduction of postweaning multisystemic wasting syndrome in gnotobiotic swine by coinfection with porcine circovirus 2 and porcine parvovirus. Vet Pathol 37:254-263.