Vaccination against Aujeszky's disease by different routes using live attenuated and inactivated virus vaccines in pigs with or without passive immunity

Epidemiology of Aujeszky disease in wild boars (Sus scrofa L.) in Croatia

Aujeszky disease (AD) or pseudorabies is a viral disease of domestic and wild animals caused by the Suid alphaherpesvirus 1. In wild boar infection usually undergo latent phase but under certain conditions reactivation of the virus can result in a disease. Seroprevalence in wild boars ranges from 0.8 to 100%, and is among other influenced by region, type of management, age and sex of the studied animals. In this study we analyzed blood, lungs, olfactory bulbs and spleen from 222 free-living wild boars from different localities in Croatia and compared results obtained by ELISA with PCR, sex, age and locality. Total seroprevalence was 33.78%, ranging from 25.26% in males to 40.15% in females (p = 0.0346; χ2 = 4.47). According to the age categories prevalence was 10% in offspring, 27.53% in subadults, and 66.75% in adults. Seroprevalence in adult males (66.66%) and females (65.30%) was almost identical. In males, significantly lower seroprevalence was detected in offspring compared to subadults (χ2 = 4.07, p < 0.05) and adults (χ2 = 31.04; p < 0.05), and in subadults compared to adults (χ2 = 15.13; p < 0.0001). Among females, adults had a significantly higher prevalence compared to offspring (χ2 = 19.27; p < 0.0001) and subadults (χ2 = 8.62; p < 0.01). Analysis between counties revealed Sisačko-moslavačka county as a hot-spot for AD. None of the samples was positive for ADV antigens. The observed trend in prevalence points to the fact that the main transmission occurs during one part of the year (most probably the mating season). Also, triggers for virus reactivation might be more complex than previously thought, since none of our samples, collected during the mating and hunting season, was PCR positive. Finally, we can conclude that adult males represent the main transmission link between different wild boar groups.

Effects of immunostimulators of microbial origin on T cells of pigs vaccinated with attenuated vaccine against Aujeszky's disease

Aujeszky's disease (AD) is a viral infectious disease caused by Suid herpesvirus 1 (SuHV-1). Vaccination and eradication of AD in domestic pigs is possible using marker vaccines with attenuated or inactivated SuHV-1, or subunit vaccines. However, vaccines with attenuated SuHV-1 have shown to be more potent in inducing strong cell-mediated immune response. The studies have shown that Parapoxvirus ovis, as well as Propionibacterium granulosum with lipopolysacharides (LPS) of Escherichia coli have pronounced immunomodulatory effects and that in combination with the vaccines can induce stronger humoral and cellular immune responses than use of vaccines alone. In our study distribution of peripheral blood T cell subpopulations was analysed after administration of vaccine alone (attenuated SuHV-1), immunostimulators (inactivated Parapoxvirus ovis or combination of an inactivated P. granulosum and detoxified LPS of E. coli) and combinations of vaccine with each immunostimulator to the 12-week old piglets. Throughout the study no significant changes were found in the proportions of γδ and most αβ T cell subpopulations analysed. However, on the seventh day of the study combination of an inactivated P. granulosum and LPS of E. coli with vaccine induced transient but significant increase of the proportions of CD4⁺CD8α⁺ and CD4^-CD8α⁺ αβ T cells, that have been strongly associated with early protection of SuHV-1 infected pigs. Our findings indicate that combination of inactivated P. granulosum and detoxified E. coli LPS could be used for enhancement of a cellular immune response induced by vaccines against AD.

Evaluation of humoral and antigen-specific T-cell responses after vaccination of pigs against pseudorabies in the presence of maternal antibodies

In this study the influence of maternal immunity against pseudorabies virus (PRV) on the development of humoral and T-cell mediated immune (CMI) responses was investigated under the experimental condition. Pigs born to immune sows were vaccinated with gE-deleted vaccine according to five different schedules. Peripheral blood mononuclear cells (PBMC), collected after vaccination, were used for PRV-induced lymphocyte proliferation assay (LPA). Antibodies to the gB and gE of PRV in serum were determined using ELISA kits. Maternally derived antibodies (MDA) in the serum of unvaccinated piglets born to immune sows were above the level considered to be positive until about 10-11 weeks of life. The active humoral as well as CMI responses was the highest in group vaccinated at 10 and 14 weeks of age. The results of this study suggest that MDA may disturb or even block development of active humoral response. Early priming of T-cells with attenuated gE-deleted PRV vaccine in the presence of MDA could be successful, but obtaining a long-term cellular immunity at least one booster is required.

Aujeszky's disease virus infection patterns in European wild boar

Evidence of exposure (i.e. seroprevalence) to Aujeszky's disease virus (ADV) is high among wild boars from south-central Spain. This research aims to determine the presence of ADV by molecular detection, and to describe the patterns of ADV infection in wild boars. Tonsils (TN) and trigeminal ganglia (TG) for ADV molecular detection, and sera were collected from wild boars (n=192) in 39 hunting estates from south-central Spain (2004/2005). A nested polymerase chain reaction (PCR) for a fragment of the ADV surface glycoprotein B was performed on collected tissues. Individual status of presence of viral DNA was tested against explanatory variables by means of a Generalized Linear Mixed Model (GLIMMIX) analysis. Viral detection prevalence was 30.6+/-6.7%. Although there was an increasing pattern with age and females presented higher prevalences, no statistically significant influence of sex and age was found for viral presence. Molecular testing in TN and TG allowed classifying infection status into (i) ADV negative (in both TN and TG), (ii) only positive in TN, (iii) only positive in TG and (iv) positive in both TN and TG. ADV DNA was statistically more frequently evidenced in TN in females than in males. With the exception of one individual, all wild boars with presence of ADV DNA in TN and TG or only in TG reacted positive in the ELISA. In contrast, animals with only ADV DNA in TN serorreacted positively and negatively. Interestingly, 45% of the PCR positive wild boars (n=59) were seronegative in the serological test, all of them with viral DNA only in TN. Our results provide evidence for latency of ADV in wild boars and stress the fact that antibody detection based tests may fail to detect a proportion of recently infected animals. This is of great concern since current management schemes in our study promote animal translocation for hunting purposes, with the associated risk of under-detecting ADV infected individuals when using serology to screen for ADV infection.

The Use of Different Vaccination Schedules for Sows to Protect Piglets against Aujeszky's Disease

Several Aujeszky's disease virus (ADV) vaccination protocols of sows were evaluated with regard to the passive protection conferred on piglets in a recently built commercial farm. Three different groups of sows were vaccinated using a Bartha K-61 strain. One group received an inactivated vaccine during pregnancy and the other two groups received attenuated vaccines, either during pregnancy (day 65) or on the seventh day of lactation. At farrowing, sows vaccinated during lactation had lower seroneutralization titres than those vaccinated during pregnancy either with inactivated or attenuated vaccines. Accordingly, their piglets were the ones with lower levels of maternally transferred neutralizing antibodies. At 4 weeks of age, five piglets born of each group of sows were challenged intranasally with a neurotropic strain of ADV. Piglets born of sows vaccinated during pregnancy with inactivated and attenuated vaccines gained 1.50 kg bodyweight and 2.50 kg bodyweight during 7 days, respectively, and did not show clinical signs, while piglets from sows vaccinated during the previous lactation lost 0.60 kg and presented moderate to severe clinical signs of ADV. Vaccination of sows during pregnancy provided more protection against ADV for piglets than sow vaccination before mating. Piglets born from sows vaccinated with attenuated or inactivated vaccines did not present remarkable differences on protection.

Vaccination with recombinant vaccinia virus vaccines expressing glycoprotein genes of pseudorabies virus in the presence of maternal immunity

Piglets which had received colostral antibody to pseudorabie virus (PRV) were divided into four groups and inoculated with a NYVAC vaccinia recombinant expressing glycoprotein gD of PRV, a NYVAC recombinant expressing glycoprotein gB of PRV, an inactivated PRV vaccine, or no vaccine. The piglets were vaccinated twice, 3 weeks apart, beginning at approximately 2 weeks of age and later challenged with virulent PRV oronasally. All three vaccines protected similarly when no maternal antibody was present. Although all three vaccines induced some active immunity in piglets with maternal antibody, piglets receiving the NYVAC/gB vaccine were the only ones protected similarly whether or not they had maternal antibodies to PRV.

Successful pseudorabies vaccination in maternally immune piglets using recombinant vaccinia virus vaccines

Three gilts were vaccinated with a NYVAC vaccinia recombinant expressing glycoprotein gD of pseudorabies virus (PRV) (NYVAC/gD). After farrowing, the piglets were allowed to nurse normally to obtain colostral immunity and then were divided into four groups, receiving NYVAC/gD, a NYVAC recombinant expressing glycoprotein gB of PRV (NYVAC/gB), an inactivated PRV vaccine (iPRV), or no vaccine. The piglets were vaccinated twice, three weeks apart beginning at approximately two weeks of age and later challenged with virulent PRV oronasally. Piglets that received NYVAC/gB or iPRV were the best protected based on lack of mortality, lower temperature responses, decreased weight loss and decreased viral shedding after challenge. These results indicate effective strategies for stimulating active immune response while still under the protection of maternal immunity.

The influence of maternal immunity on the transmission of pseudorabies virus and on the effectiveness of vaccination

The purpose of this study was to investigate whether maternal immunity could prevent transmission of pseudorabies virus (PRV) among pigs, and whether it reduced the effectiveness of a single or double vaccination with regard to the transmission of PRV. In five experiments, the transmission of PRV, expressed as the reproduction ratio R, was compared in groups of pigs with maternal immunity and in groups of pigs without maternal immunity. Transmission of PRV among unvaccinated pigs with maternal immunity (R = 0.2) was significantly lower than among pigs without maternal immunity (R = 6.3). Furthermore, maternal immunity in young pigs prevented transmission of PRV, as R was significantly below one. In once-vaccinated groups, PRV spread extensively among pigs with maternal immunity (R = 23), but did not spread extensively among pigs without maternal immunity (R = 0.6). In twice-vaccinated groups, transmission of PRV among pigs with maternal immunity (R = 0.6) did not differ significantly from the transmission of PRV among pigs without maternal immunity (R = 0.3). Thus, a single vaccination of pigs with PRV strain 783 at 10 weeks of age, when they still possessed maternal immunity, seemed not sufficient to prevent transmission of PRV. Virus transmission could be reduced, however, if maternally immune pigs were vaccinated twice at 10 and 14 weeks of age.

Vaccination of maternally immune pigs with a live Aujeszky's disease vaccine by coarse spray and other routes

33 ten weeks old passively immune weaners were inoculated with live, attenuated Aujeszky's disease (AD) vaccine, according to four different vaccination protocols: (groups A/A2) 3 x coarse spray vaccination at 10, 11 and 13 weeks of age, (groups B/B2) 1 x coarse spray at 10 weeks of age followed by 1 x intramuscularly at 13 weeks, (C) 1 x intranasal instillation at 10 weeks of age, and (groups D/D2) 2 x intramuscularly at 10 and 13 weeks of age. A further 10 weaners were included as unvaccinated controls (E/E2). Spray vaccination was technically simple to perform but on average, 20% of subjects were reluctant to expose themselves to the spray. Clinical reactions were absent apart from mild fever in one pig from group B. Weight gains between 10 and 17 weeks of age were slightly lower in group A and group B weaners, compared to control unvaccinated pigs and pigs vaccinated by other routes. Virus neutralising (VN) antibody response was extremely uneven between individuals in groups A and B. Group D pigs vaccinated 2 x intramuscularly showed a 3 week lag in developing high levels of antibody but the intramuscular route, as well vaccination by intransal instillation, proved to be the most dependable technique for inducing uniformly high levels of VN antibody. Challenge with virulent ADV at 17 weeks of age resulted in death from Aujeszky's disease of all five control pigs. One pig in group A which had no VN antibody, also died. All other pigs were protected against death.(ABSTRACT TRUNCATED AT 250 WORDS)

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

Inactivated and live Aujeszky's disease virus vaccines were administered intradermally using a special device without a needle. The 88 pigs were vaccinated at the beginning of the fattening period, both under experimental conditions and in commercial herds. All the pigs were challenged at the end of the fattening period in isolation units. The same vaccines were also injected intramuscularly. Vaccination by the intradermal route induced good protection, similar to that conferred with live virus vaccine injected intramuscularly. The inactivated virus vaccine was not as effective when it was injected by the intradermal route. In animals vaccinated intradermally, there were no local lesions in the meat, but very small nodules were found in the dermis; these do not affect carcass quality. The effects of challenge exposure depended on the initial health of the animals, and a synthetic value (delta G) was used to interpret the data. In fattening pigs, intradermal vaccination required less animal constraint than intramuscular injection; administration could be verified by the presence of a papule at the site of inoculation, and pigs could be vaccinated while they were feeding. Injection without a needle also helps avoid bacterial contamination under farm conditions.

Extent and duration of virulent virus excretion upon challenge of pigs vaccinated with different glycoprotein-deleted Aujeszky's disease vaccines

Different deleted Aujeszky's disease vaccines were compared for their ability to induce an immunity which suppresses virus excretion optimally upon infection. Groups of pigs were vaccinated once with attenuated deleted Aujeszky's disease vaccine (gI, gX or gp63 negative), suspended in phosphate buffered saline. Two additional groups were vaccinated with a gI deleted vaccine virus suspended in an oil-in-water emulsion. Other groups were vaccinated twice with gI deleted inactivated vaccines. The three control groups included were: pigs immune after infection, unvaccinated pigs and pigs receiving vaccine without known deletion in the envelope. Experimental challenge took place 3 or 4 weeks after the only or the last vaccination. The number of excreting pigs, the duration of excretion and the virus titers excreted, were determined for all the groups. All the pigs vaccinated with glycoprotein deletion vaccines suspended in phosphate buffered saline, excreted virus for 2 to 6 days after challenge. A 100 to 1000 fold reduction in excreted virus titers was obtained in vaccinated pigs compared to unvaccinated ones. Some vaccines suppressed virus excretion better than others, but no correlation could be made between the type of deletion (gI, gX or gp63) and the degree of reduction in virus excretion. Similar results were obtained with two applications of inactivated vaccines. The lowest number of excreting pigs, the lowest duration of excretion and the lowest titers were obtained in groups vaccinated with the attenuated vaccine suspended in an oil-in-water emulsion. No vaccine suppressed virus excretion totally.

Sequential changes in the humoral immune response of pigs to pseudorabies virus after vaccination, exposure to virulent virus, and reactivation of latent virus

Sequential changes in the humoral immune response of pigs to pseudorabies virus (PRV) after each of several exposures to the virus were evaluated by determining virus neutralization (VN) and radioimmunoprecipitation (RIP) activities of sera collected at selected intervals. Pigs were vaccinated intramuscularly with live attenuated virus (6 pigs), inactivated attenuated virus (6 pigs), or inactivated virulent virus (6 pigs). All pigs were challenged oronasally with virulent virus 3 weeks later and 12 (4 pigs of each vaccine group) were subsequently treated with dexamethasone in an attempt to reactivate latent virus. The relatively low serum titers of VN antibody that were raised by vaccination (titers ranged from 2 to 32) increased markedly (at least 16-fold) for all pigs after exposure to virulent virus. After dexamethasone treatment, the VN titers of 2 pigs increased 16-fold, whereas those of the other 10 dexamethasone-treated pigs and the 6 nontreated pigs either remained the same or increased only minimally (i.e., no more than 2-fold). The results of RIP using 35S-methionine-labeled viral proteins were initially similar to those of VN in that the low levels of serum RIP activity detected after vaccination increased markedly after subsequent exposure to virulent virus. In contrast to VN, however, most pigs (11 of 12) treated with dexamethasone had a clear increase in serum RIP activity. The increase was particularly striking for viral proteins of relatively low (less than 46K) molecular weight. Precipitating activity for 14C-glucosamine-labeled viral glycoproteins was not detected until after pigs were exposed to virulent virus. The increase in RIP activity detected after dexamethasone treatment was likely due to an additional antigenic stimulus associated with virus reactivation. However, virus was isolated from nasal swabs of only 4 of the 12 treated pigs. None of the results appeared to be affected appreciably by the type of vaccine used for initial immunization.

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.