Oronasal challenge of fattening pigs after vaccination with an inactivated Aujeszky’s disease vaccine

Influence of vaccine medium and vaccination schedules on the induction of active immunity against Aujeszky's disease in maternally immune pigs

Active immunity against Aujeszky's disease virus (ADV) was compared at the end of the fattening period in pigs which had been vaccinated with the attenuated Bartha strain according to different schedules in the presence of different levels of maternal immunity. The percentage of seropositive pigs at the end of the fattening period varied from 21 to 94 per cent. The percentage was significantly higher when the vaccination schedules were applied to pigs from mothers vaccinated with an attenuated strain compared to pigs from mothers vaccinated with a subunit vaccine or from infected-immune mothers. Additionally, this percentage was two to three times lower when pigs were vaccinated once at 10 weeks old compared to pigs either revaccinated at 14 weeks or vaccinated once at 14 weeks old. When the virus strain used for vaccination had been suspended either in saline or in an oil-in-water emulsion, significant differences were not found in the serological response after vaccination and in the reduction of virus excretion upon subsequent challenge. In challenge experiments, a significantly longer duration of virus excretion was observed in vaccinated pigs which had not seroconverted than in vaccinated but seropositive pigs. The vaccination schedules for sows and fattening pigs in view of the eradication of ADV are discussed.

Protection of mice and swine from pseudorabies virus conferred by vaccinia virus-based recombinants

Glycoproteins gp50, gII, and gIII of pseudorabies virus (PRV) were expressed either individually or in combination by vaccinia virus recombinants. In vitro analysis by immunoprecipitation and immunofluorescence demonstrated the expression of a gII protein of approximately 120 kDa that was proteolytically processed to the gIIb (67- to 74-kDa) and gIIc (58-kDa) mature protein species similar to those observed in PRV-infected cells. Additionally, the proper expression of the 90-kDa gIII and 50-kDa gp50 was observed. All three of these PRV-derived glycoproteins were detectable on the surface of vaccinia virus-PRV recombinant-infected cells. In vivo, mice were protected against a virulent PRV challenge after immunization with the PRV glycoprotein-expressing vaccinia virus recombinants. The coexpression of gII and gIII by a single vaccinia virus recombinant resulted in a significantly reduced vaccination dose required to protect mice against PRV challenge. Inoculation of piglets with the various vaccinia virus-PRV glycoprotein recombinants also resulted in protection against virulent PRV challenge as measured by weight gain. The simultaneous expression of gII and gp50 in swine resulted in a significantly enhanced level of protection as evaluated by weight evolution following challenge with live PRV.

Vaccination of pigs against Aujeszky's disease by the intradermal route using live attenuated and inactivated virus vaccines

A study was undertaken of the protection induced by inactivated and live Aujeszky's disease virus vaccines. The vaccines were administered using a special device which, without the use of a needle, delivered the preparation intradermally. The trials were performed on 88 pigs which were vaccinated at the beginning of the fattening period both in experimental conditions and in pig herds. All the pigs were challenged at the end of the fattening period in isolation units. The results obtained were compared with those obtained using the same vaccines injected intramuscularly. It was shown that vaccination via the intradermal route induced good protection in the vaccinated animals and was similar to that conferred by live virus vaccine injected intramuscularly. The results, with the inactivated virus vaccine, were not so good when it was injected via the intradermal route. Studies with intradermal vaccination showed no local lesion or very small nodules strictly localized to the dermis. The results also confirmed that the effects of challenge exposure depended on the health status of animals prior to infection and show the necessity to use a synthetic value (delta G) to interpret the data and mainly to compare the results objectively. In fattening pigs this vaccination procedure is attractive because (i) less animal constraint is needed than would be for intramuscular injections, (ii) injection can be checked by the presence of a visible papula at the site of inoculation and, (iii) pigs can be vaccinated in the ham while they are feeding. Injection without a needle also contributes to avoiding bacterial contamination under practical farm conditions of vaccination.

The potency testing of pseudorabies vaccines in pigs. A proposal for a quantitative criterion and a minimum requirement

A criterion for the potency testing of pseudorabies vaccine based on the difference between the mean weight gain during the seven days after pathogenic challenge of vaccinated or control piglets is proposed. This criterion, termed delta G7, has been studied as a function of initial weight variation of the animals, different challenge strains and the period between challenge and the end of the test. The statistical analysis of results optimizes the experimental parameters and gives rise to a quantitative test which discriminates between vaccinates and controls and substantiates a proposal for a minimum vaccine potency requirement. The implementation of the method proposed is compatible with current practice in control laboratories.

Aujeszky's disease vaccination and infection of pigs with maternal immunity: effects on cell- and antibody-mediated immunity

SCC, ADV-SCC, ADV-ADCC and ADV-LYST as well as ND50-titres of neutralizing serum antibodies were examined in 36 passively immune pigs, 25 of which were vaccinated at 3 weeks of age and partly revaccinated 3 weeks later. Twenty-five vaccinated animals and 8 non-immune control pigs were challenged with infectious ADV. Independent of the state of maternal immunity the cytotoxic response of the white blood cells from all the animals was low at WPP 3 but rose with increasing age. ADV-LYST occurred only in some of the animals. A single vaccination evoked no significant effect on our immune parameters, but revaccination led to higher ADV-LYST and ADV-ADCC. In pigs vaccinated at WPP 3 the neutralizing serum titres decreased gradually, similar to unvaccinated animals, indicating that the antibodies were of maternal origin. However, after vaccination at WPP 6, no further decline of ND50-titres could be detected, pointing to a limited antibody production. Animals vaccinated at WPP 3 and revaccinated 3 weeks later showed a significant increase of serum neutralizing titres. Whereas the controls showed typical symptoms of Aujeszky's disease, the immune animals, especially the unvaccinated passively immune pigs, showed only elevated temperatures and most of them excreted small amounts of ADV. The development of cellular immunity after infection was rather similar within the maternally immune group independent whether the animals had been vaccinated or not, but ADV-ADCC and ADV-LYST showed a more rapid progress within the vaccinated group than in the non-vaccinated group and the non-immune control group. Infection resulted in significantly higher ND50 titres in vaccinated and revaccinated animals than in unvaccinated animals, indicating a secondary response in those pigs. Thus, ADV sensitization of lymphocytes had been evoked by vaccination despite the presence of maternal antibody. The interpretation of the results was complicated by great individual and litter-dependent variations of the immune parameters.