Date of Award
Doctor of Philosophy
Porcine circovirus type 2 (PCV2) impacts global swine production, is economically important, and is associated with multiple disease entities that include multisystemic disease, wasting, pneumonia, diarrhea and reproductive failure. Transmission of PCV2 within or between swine populations is not well understood. We characterized semen shedding of PCV2a and PCV2b in Landrace boars and found that PCV2 viremia precedes semen shedding, clinical signs are absent, and peak PCV2 semen shedding occurs between 10-20 days post-infection. PCV2 can be continuously shed in semen for at least 90 days. We determined that PCV2 shed in semen is infectious when used in a swine bioassay model, but dam or fetal infection after artificial insemination with PCV2 positive extended semen does not necessarily occur. However, when nayve dams were artificially inseminated with PCV2-spiked semen, dam viremia and fetal infection occurred. Nayve dams inseminated with spiked semen did not show clinical signs of infection after PCV2 exposure, but increased numbers of mummified and stillborn fetuses were observed. Stillborn fetuses exhibited gross lesions of heart failure and myocardial tissue was determined to be the best sample for diagnosing in utero PCV2 infection. Using the PCV2-spiked semen model, we compared dam immunity associated with PCV2 vaccination to immunity associated with a previous infection to induce protection against subsequent PCV2-challenge. PCV2 antibodies induced by a homologous strain of PCV2 protected against in utero infection; however, 63% of the piglets from vaccinated dams were PCV2 viremic at birth suggesting that commercial vaccines may not prevent fetal infection. We also verified that PCV2 vaccination of dams is not protective against fetal infection following oro-nasal challenge during gestation, and affirmed that immunocompetent in utero fetuses are able to clear PCV2 infection prior to parturition.
Madson, Darin, "Vertical transmission of porcine circovirus type 2 in breeding herds" (2009). Graduate Theses and Dissertations. 10786.