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Intervet/Schering-Plough Animal Health IPVS Symposium 2010

Duration of Immunity Induced by a Single Dose of 2 ml Porcilis® PCV When Administered to MDA-positive Pigs at 3 Weeks of Age and Challenged with PCV2 Virus at 25 weeks of Age

Ulrike Schmidt; Frank Roerink.
Intervet/Schering-Plough International, P.O. Box 31 5830 AA Boxmeer, the Netherlands


Introduction

Porcine Circovirus type 2 (PCV2) infection in pigs is regarded as the most important causative factor in the development of Porcine Circovirus Disease (PCVD). The first description of PCVD (initially called PMWS) involved young pigs (Harding 1998). More recent articles describe infection in older pigs and it is not uncommon to observe PCVD in late stage finishers (Palzer 2009). Under field conditions the timing of PCV2 virus infection is often unknown, therefore it is important that pigs are protected for the whole of the fattening period.

PCV2 virus is widespread, and infection in sows leads to varying antibody levels in blood and colostrum. Pigs can be vaccinated early in life against PCVD in the presence of MDA. The object of this study was to demonstrate the efficacy of Porcilis PCV in piglets with MDA against PCV2 virus, following a single dose of 2 ml at 3 weeks of age. At 25 weeks of age, vaccinated and control animals were challenged with wild type PCV2 virus to investigate the extent of protection.

Materials and Methods

Progeny of SPF sows with PCV2 antibodies (ranging from 7.1 to 11.4 ELISA log2 at farrowing) were studied. Piglets were assigned to different groups of 10 piglets, so that littermates were spread evenly over the groups, with equal numbers of males and females per group. At 3 weeks of age, Group 1 was vaccinated with 2 ml of Porcilis PCV and Group 2 with placebo. At 25 weeks of age, the pigs were challenged intranasally with a heterologous wild type PCV2 challenge virus strain I-12/11.

All animals were observed daily for clinical signs and weighed several times during the study. Three weeks post challenge all animals were necropsied. At post mortem, mesenteric and inguinal lymph nodes, tonsil and spleen were sampled for the determination of PCV2 antigen and nucleic acid. Serum samples were taken at vaccination, at 10 weeks of age, at challenge and weekly thereafter until necropsy. Fecal swabs were taken at challenge and every week thereafter. Statistical analysis of the serology employed Tukey’s multiple comparison. Q-PCR data was analyzed by ANOVA using a linear mixed model, assuming a constant correlation of the repeated measurements of a subject.

Results

No differences were found between the groups for clinical signs or bodyweight, either after vaccination or after challenge.

Serology; at the time of vaccination the average titer in the PCV vaccinated group was 7.2 log2 and in the controls 7.3 log2, both above the protective antibody level (Fort 2009). By the time of the challenge, the controls had no detectable antibodies, whereas the vaccinates had titers of at least 6.9 log2 (P<0.0001). After challenge, a clear antibody response was seen in the controls but hardly any reaction in the vaccinated pigs (see table 1).

Q-PCR on serum, fecal samples and lymphoid tissues. At the time of challenge, none of the samples of either group contained detectable amounts of PCV2 DNA. After challenge, a significant reduction in the PCV2 load was found in serum, inguinal lymph nodes, spleen and tonsils of the vaccinates (P<0.05). No PCV2 DNA was detected in any of the feces samples from this group. However, PCV2 DNA was found in fecal swabs of the challenged control animals (P<0.0001). Similar findings in data generated under field conditions were reported by Toki (JSVSC 2008) and by Larsen (IPVS 2010).

Discussion

Porcilis PCV induces strong humoral and cellular immunity (Fort 20009, Martelli 2010 in press). Vaccination of MDA-positive piglets of 3 weeks of age with a single 2ml dose protects them from a heterologous challenge at 25 weeks of age. There was a significant reduction of virus shedding and PCV2 DNA load in lymphoid organs. The duration of immunity covering the whole fattening period, induced by a single dose, in the presence of MDA, is unique to Porcilis PCV. This feature has been confirmed by several field reports from different countries and forms part of the label claim for Porcilis PCV.

References

Harding; SHAP, 1998. Toki; 145th JSVSC 2008.
Palzer; Proc APVS 2009. Fort; Vaccine 2009.
Larsen; IPVS 2010. Martelli; in press 2010




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