title: Effect of vaccination with a modified-live porcine reproductive and respiratory syndrome virus vaccine on dynamics of homologous viral infection in pigs.
abstract: OBJECTIVE
  To determine effects of vaccination protocols with modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine on persistence and transmission of virus in pigs infected with a homologous isolate and determine clinical and virologic responses following heterologous viral challenge.
  
  
  METHODS
  Four hundred forty 6- to 8-week-old PRRSV-naïve pigs.
  
  
  METHODS
  Pigs were allocated into 5 groups. Groups A to D were inoculated with wild-type PRRSV VR2332. Group A (positive control pigs) received PRRSV only. Groups B, C, and D received modified-live PRRSV vaccine (1, 2, or 3 doses). Group E served as a negative control group. To evaluate viral transmission, sentinel pigs were introduced into each group at intervals from 37 to 67, 67 to 97, and 97 to 127 days postinoculation (DPI). To evaluate persistence, pigs were euthanized at 37, 67, 97, or 127 DPI. To assess clinical and virologic response after challenge, selected pigs from each group were inoculated at 98 DPI with a heterologous isolate (PRRSV MN-184).
  
  
  RESULTS
  Mass vaccination significantly reduced the number of persistently infected pigs at 127 DPI. Vaccination did not eliminate wild-type PRRSV; administration of 2 or 3 doses of modified-live virus vaccine reduced viral shedding after 97 DPI. Previous exposure to wild-type and vaccine virus reduced clinical signs and enhanced growth following heterologous challenge but did not prevent infection.
  
  
  CONCLUSIONS
  Findings suggest that therapeutic vaccination may help to reduce economic losses of PRRSV caused by infection; further studies to define the role of modified-live virus vaccines in control-eradication programs are needed.
authors.affiliation: Swine Disease Eradication Center, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108, USA.
authors.forename: Jean Paul
authors.initials: JP
authors.lastname: Cano
authors.forename: Scott A
authors.initials: SA
authors.lastname: Dee
authors.forename: Michael P
authors.initials: MP
authors.lastname: Murtaugh
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Trincado
authors.forename: Carlos B
authors.initials: CB
authors.lastname: Pijoan
mesh_terms: D000818:Animals; D019318:Porcine Reproductive and Respiratory Syndrome / Q000276:immunology / Q000517:prevention & control* / Q000821:virology*; D019316:Porcine respiratory and reproductive syndrome virus / Q000276:immunology*; D013552:Swine / Q000276:immunology / Q000821:virology; D014765:Viral Vaccines / Q000008:administration & dosage / Q000276:immunology*
chemical_list: D014765:Viral Vaccines