Effects of three commercial vaccines against porcine parvovirus 1 in pregnant gilts.

Porcine parvovirosis is a common and important cause of reproductive failure in naïve dams. Even though vaccination is generally effective at preventing disease occurrence, the homology between the vaccine and challenge strains has been recently suggested to play a role in protection. Therefore, the purpose of this study was to evaluate and compare the efficacy of three currently available commercial vaccines against porcine parvovirus genotype 1 (PPV1) in an experimental model using pregnant gilts. Seventy-seven PPV1-negative gilts were included in the trial and randomly allocated to four groups. In group 1, gilts received two doses, three weeks apart, of a PPV1 subunit vaccine (ReproCyc® ParvoFLEX). Following the same scheme, gilts from group 2 received two doses of a PPV1 bivalent vaccine (ERYSENG® PARVO). In group 3, gilts received two doses, four weeks apart, of a PPV1 octavalent vaccine (Porcilis® Ery + Parvo + Lepto). Lastly, gilts from group 4 were left untreated and were used as challenge controls. All gilts were artificially inseminated three weeks after completion of vaccination. Pregnant animals were subsequently challenged around 40 days of gestation with a heterologous PPV1 strain. Foetuses were harvested at around day 90 of gestation and evaluated for their macroscopic appearance (i.e., normal, mummified, or autolytic). Along the study, safety parameters after vaccination, antibody responses against PPV1 and viremia in gilts were also measured. All the foetuses in the challenge control group were mummified, which validated the challenge model, whereas the three evaluated vaccines protected the progeny against PPV1 by preventing the appearance of clinical manifestations associated to parvovirosis. Remarkably, the PPV1 subunit vaccine induced an earlier seroconversion of gilts and was the only vaccine that could prevent viremia after challenge. This vaccine also achieved the largest average litter size accompanied with a high average proportion of clinically healthy foetuses.

Development of a PPRV challenge model in goats and its use to assess the efficacy of a PPR vaccine.

Peste des Petits Ruminants (PPR) is a severe disease of small ruminants and has high economic impacts in developing countries. Endemic in Africa, the Middle East and Asia, the disease is currently progressing with occurrences reported in North Africa, Turkey and in Georgia, and now threatens Europe. Much remains unknown about the infection dynamics, the virulence of the different strains and species/breed susceptibility. Robust experimental challenge models are needed to explore these fields and to confirm the efficacy of currently sold vaccines. We first assessed virulence of two PPR virus strains (CI89 and MA08) in Saanen goats. Whereas the MA08 strain led to classical severe clinical signs of PPR, the CI89 strain appeared to cause a mild disease in Saanen goats, highlighting the difference in virulence between strains in this animal model. We further demonstrated the importance of the inoculation route in the appearance of clinical signs and that ocular excretion is a better choice than blood for viral detection. After developing a robust challenge model, we assessed the efficacy of a vaccine (PPR-VAC®, BVI Botswana) against the MA08 strain and demonstrated that this vaccine blocked viral excretion and significantly reduced clinical signs. These results reinforce the paradigm that a strain from one lineage could protect against strains from other lineages.

A foot-and-mouth disease SAT2 vaccine protects swine against experimental challenge with a homologous virus strain, irrespective of mild pathogenicity in this species.

FMDV serotype SAT2 is most frequently associated with outbreaks in ruminants. However, the risk of it spreading from cattle to pigs cannot be excluded. To assess the efficacy of an SAT2-type FMD inactivated vaccine against homologous challenge in pigs, a suitable challenge strain adapted to pigs was produced. After two passages in two pigs each, a FMDV stock of SAT2 challenge strain was produced. This material was used to infect two groups of five pigs. The first group being vaccinated 28 days before challenge and the other one left as an unvaccinated control. Clinical signs were recorded, virus shedding was assessed on mouth swabs, and neutralising antibody titres were determined. At least 80% of the vaccinated pigs were protected against clinical disease. Furthermore, no virus shedding was observed in any of the vaccinated pigs. This study shows that experimentally inoculated pigs can become infected with a SAT2 serotype. Furthermore, vaccination offers protection against generalisation and viral excretion, confirming the potential of vaccination as an important tool in the control of FMD in pigs.

Immunogenicity and efficacy of fowlpox-vectored and inactivated avian influenza vaccines alone or in a prime-boost schedule in chickens with maternal antibodies.

Inactivated and fowlpox virus (FP)-vectored vaccines have been used to control H5 avian influenza (AI) in poultry. In H5 AI endemic countries, breeder flocks are vaccinated and therefore, maternally-derived antibodies (MDA) are transferred to their progeny. Results of three immunogenicity and one efficacy studies performed in birds with or without MDA indicated that the immunogenicity of an inactivated vaccine based on a H5N9 AI isolate (inH5N9) was severely impaired in chicks hatched from inH5N9-vaccinated breeders. This MDA interference was lower when breeders received only one administration of the same vaccine and could be overcome by priming the chicks at day-of-age with a live recombinant FP-vectored vaccine with H5 avian influenza gene insert (FP-AI). The interference of anti-FP MDA was of lower intensity than the interference of anti-AI MDA. The highest interference observed on the prime-boost immunogenicity was in chicks hatched from breeders vaccinated with the same prime-boost scheme. The level of protection against an antigenic variant H5N1 highly pathogenic AI isolate from Indonesia against which the FP-AI or inH5N9 alone was poorly protective could be circumvented by the prime-boost regimen in birds with either FP or AI MDA. Thus, the immunogenicity of vaccines in young chicks with MDA depends on the vaccination scheme and the type of vaccine used in their parent flocks. The heterologous prime-boost in birds with MDA may at least partially overcome MDA interference on inactivated vaccine.

Interference of colostral antibodies with response to a Bluetongue serotype 8 inactivated vaccine in lambs born from hyperimmune ewes.

Despite the widespread use of Bluetongue serotype 8 (BTV-8) vaccines across Europe, there remain unanswered questions on the effects of maternally derived antibodies (MDA) on vaccination. This study investigated the persistence of MDA in lambs and their interference on vaccine efficacy. Lambs born from hyperimmune ewes-i.e. ewes naturally infected with BTV-8 in 2007 and repeatedly vaccinated thereafter-were used. They were allocated to five groups (n=7/group), four receiving a BTV-8 vaccine at different ages (3, 5, 7 and 9 months) and one left unvaccinated. Vaccine protection was assessed upon a BTV-8 challenge performed at 10 months of age. The neutralising antibody titres were also measured throughout the study. Vaccination at 5, 7 and 9 months led to seroconversion and full clinical and virological protection in all animals. Among lambs vaccinated at 3 months, three (3/7) did not respond to vaccination and were not protected from challenge infection. Others animals (4/7) were fully protected from clinical disease and viraemia in accordance with their seropositive status at time of challenge. In our very stringent conditions, MDA hampered response to BTV-8 vaccination in lambs for at least 3 months after birth. Accordingly, the optimal age of vaccination needs to be adjusted to the immune status of the sheep population.

Compatibility of turkey herpesvirus-infectious bursal disease vector vaccine with Marek's disease rispens vaccine injected into day-old pullets.

Mixtures of turkey herpesvirus (HVT) and Rispens poultry vaccines have been used worldwide for over 20 yr, mainly for vaccination of future layers and breeders. With increasing virulence of Marek's disease (MD) virus strains, vaccination strategies are evolving toward the use of vaccines combining HVT and Rispens. A single vaccination either in ovo or at 1 day of age with the HVT + infectious bursal disease (IBD) vector vaccine is efficient against IBD. However, with vaccination programs that include a hatchery administration of the HVT + IBD vaccine, additional protection against very virulent and very virulent-plus MD viruses is needed, especially for layers and breeders. This study looked at the combination of four commercially available Rispens vaccines with the HVT + IBD vector vaccine injected at 1 day of age. MD challenge tests that were superior to 90% in relative score in all the groups vaccinated with both vaccines showed that the mixture of HVT + IBD and Rispens vaccines had no effect on clinical protection against MD, and IBD challenge tests showed that the mixture of HVT + IBD and Rispens vaccines had no effect on clinical protection against IBD, which was equal to 100% protection in all the groups vaccinated with both vaccines.