Evaluation of a type 2 modified live porcine reproductive and respiratory syndrome vaccine against heterologous challenge of a lineage 3 highly virulent isolate in pigs

Abstract

Porcine reproductive and respiratory syndrome (PRRS) is one of the most common diseases in the global swine industry. PRRSV is characterized by rapid mutation rates and extensive genetic divergences. It is divided into two genotypes, which are composed of several distinct sub-lineages. The purpose of the present study was to evaluate the cross-protective efficacy of Fostera PRRS MLV, an attenuated lineage 8 strain, against the heterologous challenge of a lineage 3 isolate. Eighteen pigs were randomly divided into mock, MLV and unvaccinated (UnV) groups. The pigs in the MLV group were administered Fostera PRRS vaccine at 3 weeks of age and both the MLV and UnV groups were inoculated with a virulent PRRSV isolate at 7 weeks. Clinically, the MLV group showed a shorter duration and a lower magnitude of respiratory distress than the UnV group. The average days of fever in the MLV group was 3.0 ± 0.5, which was significantly lower than the 6.2 ± 0.5 days of the UnV group (P < 0.001). The average daily weight gains of the mock, MLV and UnV groups were 781 ± 31, 550 ± 44 and 405 ± 26 g/day, respectively, during the post-challenge phase. The pathological examinations revealed that the severity of interstitial pneumonia in the MLV group was milder compared to the UnV group. Furthermore, PRRSV viremia titers in the MLV pigs were consistently lower (101−101.5 genomic copies) than those of the UnV pigs from 4 to 14 DPC. In conclusion, vaccination with Fostera PRRS MLV confers partial cross-protection against heterologous challenge of a virulent lineage 3 PRRSV isolate.

Commercial PRRS Modified-Live Virus Vaccines

“…Although the reduction of PRRSV viremia is a critical parameter for the evaluation of PRRSV vaccines, the mechanisms of the viral clearance are still poorly understood. PRRSV viremia is often resolved even before neutralizing antibodies (NA) are detected in infected pigs [ 18 , 20 , 21 , 22 ] and vaccinated pigs [ 23 , 24 , 25 , 26 ]. Despite the low NA levels in response to PRRSV vaccination [ 23 , 24 , 27 ], pigs that received a MLV vaccine followed by a PRRSV challenge still efficiently cleared PRRSV in the blood.…”

“…Measurement of IFN-γ secreting cells (IFN-γ-SC) is a frequently used tool for evaluating the recall IFN-γ responses after vaccination or infection. Numerous vaccinate-challenge studies found a significant negative correlation between the IFN-γ response and blood viral load, indicating induction of IFN-γ responses by MLV vaccine may result in the reduction of viremia [ 23 , 25 , 26 , 32 , 33 , 34 , 35 ]. Cell-mediated immune response is therefore an important component in the clearance of PRRSV viremia.…”

“…These results provide swine practitioners and producers with clinically significant information as the rapid evolution of PRRSV is an important driving force for the emergence of new strains capable of vaccine resistance [ 51 ]. The second MLV2 vaccine introduced into the market has been shown to reduce viremia levels and nasal shedding as well as reduce the severity of PRRSV-induced lesions following a challenge with a variety of PRRSV-2 strains from Asia and North America [ 23 , 26 , 48 , 52 ].…”

Porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) genetic diversity and occurrence of wild type and vaccine-like strains in the United States swine industry

“…Additionally, vaccine strains were compared only to sequences within the same lineage to illustrate its potential impact on lineage diversity. However, the decision of which vaccine will be used is not necessarily lineage-based, as PRRSV lineage classification has only recently gained traction for routine diagnosis and vaccines show variable heterologous protection, particularly in reducing clinical signs and lesions against unrelated isolates [30][31][32]. We decided to use an arbitrary <5% nucleotide identity to a vaccine-strain as cutoff to define vaccine-like sequences instead of their relative distances to the parental or vaccine strains, the latter of which could be interpreted as a metric of the overall divergence of the virus.…”

Porcine Reproductive and Respiratory Syndrome Modified Live Virus Vaccine: A “Leaky” Vaccine with Debatable Efficacy and Safety

“…The limited efficacy of cross-protection from commercial MLV vaccines against NADC30-like viruses might be an important reason that these viruses widely spread and became the predominant PRRSV strains in China [ 117 , 119 , 120 , 121 ]. Furthermore, the Fostera ® PRRS MLV from lineage 8 of PRRSV-2 is also confirmed to confer partial cross-protection against the heterologous challenge of a virulent PRRSV strain from lineage 3 [ 122 ]. To improve the heterologous protection efficacy, some immune boosters or regulators, such as quercetin and Quil A, which are regarded to be able to upgrade the mRNA expression of interferon and many other helpful cytokines, were orally taken or injected together with PRRS MLV.…”