Differential detection of classical swine fever virus challenge strains in C-strain vaccinated pigs

Abstract

BackgroundControl 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.ResultsIn 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.ConclusionsGenetic 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.

Mapping B-cell responses to Salmonella enterica serovars Typhimurium and Enteritidis in chickens for the discrimination of infected from vaccinated animals

“…One option is to identify genetic differences between vaccine strains and circulating wild-type strains of a pathogen. However, such assays can be relatively complicated and can be compromised by genetic mutations in the wild type pathogen 15 16 .…”

“…Both libraries display random 9 amino acid peptides on coat protein VIII and have diversities of ~10 7 , one library displays linear peptides and the other displays peptides constrained between two cysteine residues. Panning was carried out as previously described 16 . Briefly, libraries were pooled and panned against IgY (20 μg/ml immobilised on 10 maxisorb plastic microtitre wells per sample) from each of 10 chickens infected with S .…”

A Critical Review about Different Vaccines against Classical Swine Fever Virus and Their Repercussions in Endemic Regions

“…The former have shown problems with the sensitivity of the test as well as cross-reactivity with other CSFV-related pestiviruses, including BVDV and BDV, which have limited its use [157]. It is important to highlight that several efforts have been made in order to optimize the performance of this assay [160][161][162]. However, PrioCHECK CSFV Erns (Thermo Fisher Scientific (former Prionics), USA) still exhibited deficiencies in terms of sensitivity and specificity, as well as robustness and reproducibility [115,117].…”

“…Another differential assay has been developed that can distinguish the genetically similar Riems C-strain and HCLV and LPC vaccine strains from most field strain genotypes except some of the genotype 3 strains [170]. In addition, a differential real-time RT-PCR assays specifically designed to detect the individual challenge strains were developed [160]. On the other hand, the current emergence of isothermal amplification assays including loop-mediated isothermal amplification system (LAMP), which have been already applied for the diagnostic of CSFV [19], or recombinase polymerase amplification (RPA) have opened new opportunities to the development of DIVA assays.…”

Recent Advances in the Diagnosis of Classical Swine Fever and Future Perspectives

“…The rationale of genetic DIVA (differentiation of infected from vaccinated animals) is the identification of genetic differences between vaccine strains and wild-type CSFVs. Both traditional RT-PCR and real-time RT-PCR (single-plex or multiplex)-based CSF genetic DIVA systems have been developed and evaluated [ 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 ]. Multiplex nested RT-PCR and real-time RT-PCR assays have been developed for differential detection of wild-type virus from C-strain vaccine [ 62 , 63 , 64 , 65 , 66 , 67 , 68 ].…”