Study of the virulence and cross-neutralization capability of recent porcine parvovirus field isolates and vaccine viruses in experimentally infected pregnant gilts.

The pathogenicity of two recent German field isolates of Porcine parvovirus (PPV-27a and PPV-143a) and two vaccine viruses [PPV-NADL-2 and PPV-IDT (MSV)], which are used for the production of inactivated vaccines, was investigated by inoculation of pregnant sows at day 40 of gestation. Post-infection sera of these sows as well as antisera prepared in rabbits by immunization with the four above-mentioned PPV isolates and with the virulent strain PPV-Challenge (Engl.) were tested for their homologous and heterologous neutralization activities. All antisera had high neutralization activity against the vaccine viruses, the PPV-Challenge (Engl.) virus and PPV-143a, but much lower activity against PPV-27a. These results suggest that PPV-27a represents a new antigenic variant or type of PPV and vaccines based on the established vaccine viruses may not be fully protective against this field isolate. PPV-27a has been characterized based on the amino acid sequences of the capsid protein as a member of a new and distinct PPV cluster (Zimmermann et al., 2006). Interestingly, the homologous neutralizing antibody titres of the sera of all three pigs and both rabbits inoculated or immunized with PPV-27a were 100- to 1000-fold lower than the heterologous titres against any of the other viruses. The low homologous neutralizing antibody titres suggest a possible, yet undefined, immune escape mechanism of this PPV isolate.

Tissue distribution of two field isolates and two vaccine strains of porcine parvovirus in foetal organs after experimental infection of pregnant sows as determined by real-time PCR.

The aim of this study was to investigate the tissue distribution of two different field isolates and two vaccine strains of porcine parvoviruses (PPV) in infected piglets after transplacental infection. The viral load in 10 different foetal organs was determined by real-time polymerase chain reaction assays with SYBR Green targeting the viral VP2 gene and the genomic c-myc gene in 12 foetuses. The viral load in foetal tissues differed greatly among the different parvoviruses. Between one virulent field isolate compared with the other field isolate and the vaccine strains, the detected viral copy number differed in an order of magnitude of 10(9). The virulent isolate contained PPV in all 10 organs with viral loads varying between 10(11) and 10(15) per 10(6) cells. Concerning the other field isolate and the two vaccine strains, if PPV was detected, in most of the cases the highest viral load was found in foetal kidneys with a maximum viral load of 10(3) per 10(6) cells. Additionally, PPV was found in the heart of one foetus, in the liver and duodenum of one foetus and in the thymus of one foetus with viral loads varying between 10(2.1) and 10(3.5) per 10(6) cells. In completely mummified foetuses with no discriminable organs of foetuses infected with the vaccine strains and the less virulent isolate, PPV was present in very low amounts or even below the detection limit.