Vaccine-related protection against PCV2 fetal infection in conventional gilts.

From previous investigations a low antibody titre and a prolonged viremia in non-vaccinated compared to vaccinated gilts revealed to be the higher risk factor associated to fetus infection in conventional animals inseminated with PCV2 spiked semen. A trial was performed to compare antibody titres, viremia, fetuses and fetal membranes/fluids samples PCV2 positivity in four groups of conventional gilts: 6 vaccinated with a commercial inactivated PCV2 vaccine (VAI), 6 vaccinated with a commercial vaccine based on a ORF2 capsid protein expressed in a baculovirus system and licensed for use in piglets (VBI), 6 non vaccinated (NVI) and 3 non-vaccinated and non-infected controls (CTR). Both types of vaccines were administered in gilts at 120 and 150 days of life. All animals received Regumate® for 18 days followed by an estrus syncronization and superovulation protocol. VAI, VBI and NVI groups were inseminated with a double (24 hrs apart) dose of PCV2 negative semen spiked with a PCV2b strain isolated in a PMWS outbreak in Italy. CTR gilts were fecundated with a double dose of PCV2 free semen. PCV2 in tissues was assessed and quantified by real time PCR. In the VAI group 4 out of 6 gilts were pregnant, in VBI 3 out of 6, in NVI 3 out of 6 and in CTR 2 out of 3, from which were collected 25, 19, 33 and 20 fetuses, respectively and corresponding placenta membranes and amniotic fluid. No differences in antibody titres nor viremia were revealed among groups during the trial. CTR showed the significantly (P<0.05) lowest proportion of PCV2 positive samples in fetuses, amniotic fluids and placentas compared to the other groups. In the experimentally infected animals, compared to NVI, gilts of the VAI group showed a significantly (P<0.05) lower proportion of positivity in fetuses (VAI 21.74 vs NVI 48.48) but not in amniotic fluid (VAI 17.39 vs NVI 33.33) and placentas (VAI 73.91 vs NVI 72.73), while in VBI group the percentages of samples positive to PCV2 genome were significantly higher (P<0.05) in amniotic fluid (VBI 68.42 vs NVI 33.33), placentas (VBI 100 vs NVI 72.73) but not in fetuses (VBI 36.84 vs NVI 48.48). Comparing the two vaccinated groups, a significant difference was found as for the percentages of samples positive to PCV2 genome in amniotic fluid (VAI 17.39 vs VBI 68.42), placentas (VAI 73.91 vs VBI 100) but not in fetuses (VAI 21.74 vs VBI 36.84). In the present experimental conditions with a very severe challenge, vaccination with vaccine A did not eliminate but significantly reduced the risk of fetuses contamination. Considering the most common way of foetus infection thorough the foetal membranes/fluids, the protective role of the two vaccines does not seem to be similar. The lowest percentage of placentas and amniotic fluid infected in VAI compared to VBI groups can explain the lowest foetal positivity to PCV2 in this group of gilts compared to NVI animals.