The control of BVDV is based on strict biosecurity, eradication efforts (identification and removal of PI cattle) and vaccination, or a combination of these factors. One of the main goals of vaccination against BVDV is to prevent persistent infection [18].
The aim of this study was to investigate the effectiveness of live-attenuated (MLV) monovalent vaccine against BVDV, licensed for sale in Poland. Our study showed that one dose of a commercial MLV vaccine ensures protective level of antibodies in all vaccinated animals, which emerges as soon as one month after vaccination and remains stable for at least a year. The VNT titers of 20 which is considered as protective [19, 20] was reached in all cows 2 months after vaccination and it was maintained for the entire study period. The results of VNT were strongly positively correlated with the results of ELISA, which indicates that both tests yield consistent results.
In our study a neutralizing antibody response was detected in vaccinated animals one month after vaccination, reaching a peak of 4.3 log2. The antibody titer was significantly higher (5.8 log2, p < 0.05) a month later. It was reported strong and durable seroneutralizing response one month after Mucosiffa® vaccine administration. Moreover no virus was detected in the foetus, no viremia (cellular and plasmatic) and no leucopenia/lymphocytopenia were observed after challenge of non-cytopathic BVDV-1f22146/Han81 strain [21]. From the other hand the vaccination with Mucosiffa® vaccine could induce an adequate level of neutralizing antibodies to BVDV-2 (seroconversion) and produce protection against an experimental infection with BVDV-2 [22]. The Bovela® vaccine containing both BVDV types 1 and 2 strains induced VN antibody titers to BVDV-1 similar to the field strain FSV B90 BVDV-2 in 5th and 6th week post vaccination. However the antibody titers to BVDV-2 were significantly lower (p < 0.05) for Bovela® group than for the FSV group in 5th, 6th and 7th week after vaccinations [23]. From the other hand the seroneutralizing response resulting from vaccination with MLV vaccine, are generally lower than those resulting from natural exposure but follow similar development and decay curves [24].
Selection of BVDV vaccines is based on ability to protect against acute infection and to protect the developing foetus [25]. It was demonstrated that live BVDV vaccines are able to pass the placental barrier [26] and could replicate in the foetus [27] which provides active immunization against transplacental BVDV infection of the foetus. However, administration of live-attenuated vaccine has not provided 100% protection of the foetus [28].
Although vaccination does not always induce measurable antibodies in all individuals, BVDV vaccination increases herd immunity, so that the incidence of clinical disease and the birth of PI animals are reduced. The number of cows which we enrolled in our study provides very trustworthy information that at least three-fourths of cows in this herd mounted similar serological response to the vaccination. Moreover, if exposure occurs vaccination will also reduce the spread of BVD virus in the herd [14]. Independently from the vaccination the regular monitoring of the farms should be, undertaken as part of the BVDV control program.
The ability of MLV vaccines to induce an adequate neutralizing antibody titers is mainly associated with reduction of viremia and viral shedding. However, the use of live-attenuated vaccines have been limited due to the use of BVDV contaminated fetal bovine sera (FBS). These live vaccines have the potential to increase the transmission of the virus and cause disease outbreaks in susceptible animals [14]. A raw FBS testing for the presence of BVDV before Gamma irradiation is demanded by most biopharmaceutical companies, which is required by the EU regulation Directive for Pharmaceutical Raw Material of Bovine Origin (EMEA-CPMP-BWP-1793-02). However, some FBS producers that want to avoid the risk that their products will not be approved for use in the production of bioproducts irradiate raw FBS prior to testing for BVDV, without disclosing this information to the biopharmaceutical companies [29]. Antos at al. [30] examined commercial FBS available on the local Polish market and in immunoprophylaxis and diagnostics in Poland. Only one serum showed the presence of an infectious virus and was contaminated with all three species of BVDV. According to the declaration of the producer, it was an inactivated vaccine against IBR.