Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2011
Publication Date: 7/15/2011
Citation: Opriessnig, T., Madson, D.M., Schalk, S., Brockmeier, S., Shen, H., Beach, N.M., Meng, X.J., Baker, R.B., Zanella, E.L., Halbur, P.G. 2011. Porcine circovirus type 2 (PCV2) vaccination is effective in reducing disease and PCV2 shedding in semen of boars concurrently infected with PCV2 and Mycoplasma hyopneumoniae. Theriogenology. 76(2):351-360. Interpretive Summary: Porcine circovirus (PCV2) is associated with multiple disease syndromes of swine, such as a wasting syndrome and the porcine respiratory disease complex, and is of increasing concern to producers around the world. Much remains unknown concerning how this virus is transmitted and causes disease. The majority of swine farms today have PCV2 while only a small percentage of them have actually shown signs of PCV2-associated disease. Researchers have learned that simply inoculating pigs with the virus will not reliably reproduce clinical disease. So, while PCV2 is strongly implicated in several disease syndromes, co-infection with other pathogens or appropriate environmental and management conditions must exist for the diseases to become apparent. ARS scientists at the National Animal Disease Center in Ames, Iowa in collaboration with scientists at Iowa State University determined that boars experimentally co-infected with PCV2 and the respiratory bacterial pathogen Mycoplasma hyopneumoniae can develop and clinically manifest porcine circovirus associated disease (PCVAD) and shed larger amounts of PCV2 in their semen. In addition, PCV2 vaccinated boars did not develop clinical disease and had significantly reduced PCV2 shedding in semen. This information defines conditions under which PCV2 can cause disease and mechanisms of transmission and will guide boar stud owners in their decision process when considering PCV2 vaccination.
Technical Abstract: The objectives of this study were to determine if the amount of porcine circovirus type 2 (PCV2) shed in semen will be increased in boars experimentally coinfected with Mycoplasma hyopneumoniae (MHYO) and if PCV2 vaccination of the boars prior to PCV2 exposure will result in reduced PCV2 viremia and virus shedding in semen. Twelve specific-pathogen-free PCV2- and MHYO-naive boars were randomly assigned to one of four groups. A portion of the boars were vaccinated against PCV2 (VAC) on Day 0 and/or inoculated with MHYO on Day 21 and all boars were challenged with PCV2 on Day 35. The four treatment groups included PCV2-I (n=3), VAC-PCV2-I (n=3), MHYO-PCV2-Coinfected (Co-I) (n=3), and VAC-MHYO-PCV2-CoI (n=3). Semen, blood swabs, feces, and serum samples were collected weekly until Day 70. All vaccinated boars seroconverted to PCV2 by Day 35. Between Days 28 and 35, MHYO boars developed moderate respiratory disease characterized by coughing, respiratory distress, mucopurulent nasal discharge, loss of body condition and on Day 50, 1/3 MHYO-PCV2-CoI boars became lethargic and died. PCV2-I and MHYO-PCV2-CoI boars had significantly higher PCV2 DNA loads in blood swabs compared to VAC-PCV2-I and VAC-MHYO-PCV2-CoI. Moreover, PCV2 vaccination resulted in significantly reduced incidence and amount of PCV2 shedding in semen and feces. In summary, coinfection of boars with PCV2 and MHYO resulted in severe clinical disease and shedding of high amounts of PCV2 in semen. Viral shedding was significantly decreased by PCV2 vaccination. This information will be useful to guide boar stud and breeding herd managers in their decision making process when considering the use of PCV2 vaccines.