Examination of viraemia and clinical signs after challenge with a heterologous PRRSV strain in PRRS Type 2 MLV vaccinated pigs: A challenge-dose study

PLoS One. 2018 Dec 28;13(12):e0209784. doi: 10.1371/journal.pone.0209784. eCollection 2018.

Abstract

Vaccination with porcine reproductive and respiratory syndrome (PRRS) Type 2 modified-live vaccines (MLVs) has been shown to improve clinical signs and survival rates in PRRS virus (PRRSV)-challenged pigs. This study evaluated the dose of PRRSV challenge needed to cause and maintain viraemia in PRRS Type 2 MLV-vaccinated pigs and assessed clinical responses to various doses of virulent challenge. This controlled, randomised, blinded vaccination-challenge study involved 95 pigs who were either vaccinated with 2 mL of a PRRS Type 2 MLV on Day 0 or left unvaccinated. On Day 28, pigs were challenged intranasally with virulent PRRSV isolate (dose range <1.5 to 4 log10 50% tissue culture infectious dose/mL). Five pigs were left unchallenged and served as environmental controls. Viraemia levels, pyrexia, average daily weight gain and clinical signs were assessed. At all challenge doses, vaccinated groups had reduced viraemia levels and clinical signs, and higher average daily weight gain compared with non-vaccinated groups. Vaccinated groups challenged with ≤2 log had similar viraemia levels and clinical performance (days pyrexic and average daily weight gain) as the non-challenged group. Vaccinated groups had significantly reduced pyrexic days compared with non-vaccinated groups across all challenge doses (P <.05). Vaccinated pigs challenged with <3 log had significantly improved average daily weight gain (P <.05). In vaccinated groups, challenge dose correlated positively with viraemia levels and number of days pyrexic, and negatively with average daily weight gain. This is the first study to use a challenge-dose model to evaluate the efficacy of vaccination against PRRSV. PRRS Type 2 MLV was shown to mitigate the consequences of PRRSV infection at all evaluated PRRSV challenge doses. Lower levels of challenge had minimal impact on health and performance of vaccinated pigs, supporting the benefit of vaccinating swine with PRRS Type 2 MLV.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Intranasal
  • Animals
  • Antibodies, Viral / immunology
  • Porcine Reproductive and Respiratory Syndrome / virology
  • Porcine respiratory and reproductive syndrome virus / immunology
  • Porcine respiratory and reproductive syndrome virus / pathogenicity*
  • Random Allocation
  • Swine
  • Viral Vaccines / immunology
  • Viremia / immunology
  • Viremia / virology*

Substances

  • Antibodies, Viral
  • Viral Vaccines

Grants and funding

All authors are employees of Boehringer Ingelheim, who funded the study and developed one of the vaccines evaluated in this study. This commercial affiliation does not alter our adherence to PLOS ONE policies on sharing data and materials. The funder provided support in the form of salaries for authors GH, JH, MR, BF, RP and AP, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section of this manuscript. The author(s) received no specific funding for this work.