title: Differential detection of classical swine fever virus challenge strains in C-strain vaccinated pigs.
abstract: BACKGROUND
  Control of classical swine fever (CSF) by vaccination ideally requires that field strain infection can be detected irrespective of the vaccination status of the herd. To inform on the usefulness of molecular tests compatible with genetic Differentiation of Infected from Vaccinated Animals (DIVA) principles when using live-attenuated vaccines, tonsil homogenates from a vaccination-challenge experiment were analyzed using a differential real-time qRT-PCR for the C-strain vaccine or real-time qRT-PCR assays developed to specifically detect the challenge strains used.
  
  
  RESULTS
  In animals with high or moderate levels of blood viraemia, which were not, or not fully, protected by vaccination, challenge virus RNA was readily detected in tonsil homogenates. In three out of the seven vaccinated animals that had high or moderate viraemia, the vaccine strain RNA also could be detected but at lower levels. Lower but varying levels of challenge and/or vaccine virus RNA were detected in tonsil homogenate samples from animals with no or low-level viraemia, and in groups solely consisting of such animals, no transmission of infection to naïve in-contact animals occurred. In one group of animals that were vaccinated 3 days prior to challenge, viraemia levels varied from high to absent and transmission of challenge virus to naïve in-contact animals occurred. The DIVA assay revealed challenge virus in all tonsil homogenates from this group, even in those animals that did not have viraemia and were protected from clinical disease by vaccination. Such animals, particularly in a low biosecurity/informal farm setting, could constitute a risk for disease control in the field.
  
  
  CONCLUSIONS
  Genetic DIVA testing is useful for detecting the presence of field virus infection especially in non-viraemic animals without overt clinical signs but which are incompletely protected by vaccination. Such tests could particularly be useful to inform decisions prior to and during cessation of a control strategy that employs vaccination.
authors.affiliation: Virology Department, APHA, New Haw, Addlestone, KT15 3NB, UK. Helen.Everett@apha.gsi.gov.uk.
authors.forename: Helen E
authors.initials: HE
authors.lastname: Everett
authors.affiliation: Virology Department, APHA, New Haw, Addlestone, KT15 3NB, UK. bentley.crudgington@apha.gsi.gov.uk.
authors.forename: Bentley S
authors.initials: BS
authors.lastname: Crudgington
authors.affiliation: Virology Department, APHA, New Haw, Addlestone, KT15 3NB, UK. bukisoule@gmail.com.
authors.forename: Olubukola
authors.initials: O
authors.lastname: Sosan-Soulé
authors.affiliation: Virology Department, APHA, New Haw, Addlestone, KT15 3NB, UK. helen.crooke@apha.gsi.gov.uk.
authors.forename: Helen R
authors.initials: HR
authors.lastname: Crooke
mesh_terms: D000818:Animals; D006691:Classical Swine Fever / Q000175:diagnosis* / Q000276:immunology / Q000517:prevention & control / Q000821:virology; D006692:Classical Swine Fever Virus / Q000235:genetics / Q000276:immunology; D014066:Palatine Tonsil / Q000821:virology; D060888:Real-Time Polymerase Chain Reaction; D013552:Swine / Q000276:immunology / Q000821:virology; D014765:Viral Vaccines / Q000276:immunology* / Q000627:therapeutic use; D014766:Viremia / Q000276:immunology / Q000662:veterinary / Q000821:virology
chemical_list: D014765:Viral Vaccines