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United States Department of Agriculture

Agricultural Research Service

Research Project: SWINE VIRAL DISEASES PATHOGENESIS AND IMMUNOLOGY Title: Leukogram abnormalities in gnotobiotic pigs infected with porcine circovirus type 2

Authors
item Gauger, Phillip
item Lager, Kelly
item Vincent, Amy
item Opriessnig, T -
item Cheung, Andrew
item Butler, John -
item Kehrli Jr, Marcus

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 21, 2011
Publication Date: December 29, 2011
Citation: Gauger, P.C., Lager, K.M., Vincent, A.L., Opriessnig, T., Cheung, A.K., Butler, J.E., Kehrli, Jr., M.E. 2011. Leukogram abnormalities in gnotobiotic pigs infected with porcine circovirus type 2. Veterinary Microbiology. 154(1-2):185-190.

Interpretive Summary: Porcine circovirus type 2 (PCV2) is the causative agent of porcine circovirus associated disease, a disease complex affecting swine around the world. Although this virus is believed to negatively affect the host's immune system, the mechanism by which it induces disease is not completely understood. This report describes a series of experiments using the germ-free pig model in which a relationship was found between the development of clinical disease in PCV2-infected pigs, and the development of abnormal white blood cell counts, cells that are part of the immune system. The abnormal white blood cell counts were first detected about 14 days post infection with a reduction in the number of lymphocytes, one type of white blood cell. This change was followed by an increase in neutrophils, a different type of white blood cell. This increase in neutrophils and decrease in lymphocytes developed prior to pigs becoming sick and these changes could be used to predict the onset of disease. In contrast, when the white blood cell count remained normal pigs did not become sick. Although the mechanism linking the abnormal white blood cell counts with disease is not known, it appears there is a direct effect of PCV2 on some cells in the immune system.

Technical Abstract: Porcine circovirus type 2 (PCV2) is a single-stranded circular DNA virus that is the causative agent of porcine circovirus associated disease (PCVAD), a disease complex affecting swine around the world. Although this virus is believed to negatively affect the host's immune system, the mechanism by which PCV2 induces disease is not completely understood. This report describes a series of PCV2 experiments using the germ-free pig model in which a correlation was noted between abnormal leukograms and development of clinical disease in PCV2-infected pigs. The leukogram was characterized by a lymphopenia beginning within 14 days post inoculation (dpi) followed by an absolute neutrophilia approximately one week later. No significant changes in the circulating monocyte, basophil, and eosinophil cell populations were detected. The combination of an absolute neutrophilia and lymphopenia produced a neutrophil/lymphocyte ratio that was predictive of clinical disease and was inversely correlated with the presence of neutralizing antibodies. Based on previous reports, the lymphopenia may be attributed to a direct cytolytic effect of the virus and could negatively affect the pig's immune response. The role of the neutrophilia in the pathogenesis of PCVAD in germ-free pigs is not known.

Last Modified: 9/20/2014
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