CategorySwine Health - General Disease
Date Full Report Received07/22/2009
Date Abstract Report Received07/22/2009
Funded ByNational Pork Board
Temporal evidence correlated the emergence of PCV2b in the U.S. in 2005 with more frequent and severe porcine circovirus associated disease (PCVAD) cases. Information on the quantity and duration of PCV2b DNA in various biological samples is vital to understanding the virulence of this isolate. As PCV2 is known to be present in blood, the recent outbreaks have raised concern about the spread of PCV2 in spray-dried plasma protein products in the feed. This has led some producers and practitioners to discontinue the use of plasma protein on their farms. As research makes a stronger case for fecal-oral transmission of PCV2, producers have also become concerned over introduction of new PCV2 strains by means of transport vehicles. In order to determine if PCV2b was present in the US prior to 2005, tissue samples collected on different farms in the Midwest from pigs (n=81) suspected to have clinical PCVAD during 2002 and 2003 were analyzed. To determine shedding patterns, 4 groups of 9-week-old, conventional SPF pigs were inoculated as follows: Group 1 (n=7) negative controls, Group 2 (n=6) inoculated with virulent PCV2a isolate, Group 3 (n=6) inoculated with PCV2b, and Group 4 (n=6) inoculated with a less virulent PCV2a isolate. Blood samples were collected weekly for two weeks following infection. To determine the quantity and infectivity of PCV2b, five pigs were inoculated with PCV2b isolate NC-16845 at three weeks of age (positive control). Twenty-eight PCV2 naïve pigs either remained un-inoculated or were inoculated by various routes (intraperitoneal, intranasal, oral, intramuscularly or oral gavage) with either pooled nasal, oral, or fecal samples or with a contaminated needle collected from the positive control pigs. Blood samples were collected weekly for 42 days following infection to determine viremia and the serological response. To determine whether spray-dried plasma is infectious, twelve three-week-old, colostrum-fed, crossbred, specific-pathogen-free (SPF) conventional pigs were divided into groups of three and placed into separate rooms. Pigs were left un-inoculated (NEG), inoculated intraperitoneally with a reconstituted spray-dried plasma product (SDP-IP), inoculated intraperitoneally with PCV2 infected plasma (POS) or inoculated with reconstituted SDP via oral gavage (SDP-OG). Blood samples were collected weekly following inoculation for 7 weeks and tested for the presence of anti-PCV2-IgG antibodies and PCV2 DNA. To determine the efficacy of various trailer disinfection methods, three model trailers were designed and manufactured by Eby Trailers. The models were constructed with identical materials found in full-size trailers. The trailers were contaminated with feces collected at the time of euthanasia from a pig exhibiting clinical signs of PCVAD. Trailers which were disinfected (all trailers excluding positive controls) were power-washed and rinsed similar to commercial washing procedures. After washing, the following disinfectants were applied per manufacturer’s instructions: (1) Synergize, (2) Virkon, (3) Quatricide, and (4) Virkon followed by Bleach. Two naïve pigs were placed into each trailer for a total of 2 hours followed by placement into separate rooms and monitoring by ELISA and PCR for evidence of PCV2 seroconversion and viral replication for 42 days. While the differences in clinical signs apparent under field conditions in 2004 and 2005 may be correlated with the emergence of PCV2b in the United States, consistent differences between the amount of PCV2a and PCV2b shed in nasal, oral and fecal routes were not noted. Secondly, PCV2b was recovered from only two of 81 samples from PCVAD cases submitted between 2002 and 2003. This data suggests that PCV2b was not the predominant strain prior to the severe PCVAD cases seen in 2005. In the current study, peak shedding of PCV2b in experimentally infected pigs in oral, nasal and fecal samples appeared at DPI 16, 16 and 19 respectively. Intraperitoneal inoculation with contaminated fecal, nasal and oral excretions resulted in viremia and seroconversion in all animals by 28 and 42 days post inoculation (DPI), respectively. Intranasal inoculation of nasal secretions resulted in seroconversion and viremia in all animals by DPI 35 and 28, respectively. Feces fed to naïve animals resulted in viremia and seroconversion in 2 of 4 animals by DPI 35 and 42, respectively. Viremia and microscopic lesions were noted in one animal inoculated with a contaminated needle; however, seroconversion was not detected. The current study provided evidence that spray-dried plasma is indeed infectious as evidenced by seroconversion and viremia following intraperitoneal injection and oral gavage. Finally, to mimic commercial transportation conditions, three model trailers were designed and manufactured by a commercial company to possess the best features for virus survival (seams, gates, etc.). Results of the study indicated that in all disinfection protocols were equally able to prevent seroconversion and viremia in naïve animals for 49 days.
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