Immune response of sows and their offspring to pseudorabies virus: serum neutralization response to vaccination and field virus challenge.

One month prior to breeding, sows were vaccinated with an attenuated pseudorabies virus vaccine or challenged with a field strain of pseudorabies virus. A third group of sows were not vaccinated or challenged before breeding. Pigs from these sows were vaccinated at 3, 6, or 12 weeks of age and challenged with virulent virus three weeks later. One pig from each litter served as an unvaccinated, unchallenged control. Serum neutralization titers of these pigs were monitored from birth until 22 weeks of age. Titers of the sows were monitored through breeding, gestation and farrowing. The maximum prefarrowing anti-pseudorabies virus titer in the field virus challenged sows occurred four weeks following challenge. A significant decline in titers occurred at farrowing. Titers rose from one week postfarrowing and then declined. Titers in the field virus infected sows were consistently two to threefold greater than those of the vaccinated sows. The maximum prefarrowing anti-pseudorabies virus titer in the vaccinated sows occurred six weeks following vaccination. The geometric mean titer in these sow's then decreased and increased for two weeks after farrowing. The results in the pigs can be summarized as follows: Pigs from control sows had a greater serological response following field virus challenge than following vaccination with a modified live virus. Pigs from control sows responded serologically to vaccination at 3, 6 and 12 weeks of age. Pigs from control sows which were challenged at 6, 9 and 15 weeks of age had similar antibody responses. Pigs from vaccinated sows had no increase in titer following vaccination at three and six weeks of age. Titers increased when these pigs were vaccinated at 12 weeks of age. There was no significant increase in mean titers of pigs from challenged sows following vaccination at 3, 6 and 12 weeks of age. Vaccinated pigs from control and vaccinated sows had a secondary response following challenge three weeks after vaccination.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protection against enteric colibacillosis in pigs suckling orally vaccinated dams: evidence for pili as protective antigens

Pregnant gilts were vaccinated orally with Escherichia coli that produced pilus antigens K99 or 987P. The vaccines were live or dead enterotoxigenic E coli (ETEC) or a liver rough non-ETEC strain which has little ability to colonize pig intestine. Pigs born to the gilts were challenge exposed orally with K99+ or 987P+ ETEC, which did not produce heat-labile enterotoxin or flagella and which produced somatic and capsular antigens different from those of the vaccine strains. Control gilts had low titers of serum and colostral antibodies against pilus antigens, and their suckling pigs frequently had fatal diarrhea after challenge exposure. Serum antibody titers against pilus antigens of the vaccine strains increased in the gilts after vaccination with liver ETEC, and the colostral antibody titers of these gilts were higher than those of controls. Pigs suckling such vaccinated gilts were more resistant than controls to challenge strains were of different pilus types, and it could not be attributed to enterotoxin neutralization by colostrum. In contrast to the live ETEC vaccines given to the pregnant gilts, the liver rough non-ETEC and dead ETEC vaccines stimulated little or no production of antibody against pilu, and the pigs born of these vaccinated gilts remained highly susceptible to challenge exposure. The results support the hypothesis that pilu can be protective antigens in oral ETEC vaccines. It was indicated that in the system reported, protection depended on living bacteria for the production of pilus antigens in vivo or for the transport of pilus antigens across intestinal epithelium.     

In vivo and in vitro reactivation of latent pseudorabies virus in pigs born to vaccinated sows

Latency of pseudorabies virus (PRV) was established in 8 of 9 pigs born to 2 vaccinated sows. Pigs had high, low, or no maternal antibody titers at the time of the initial inoculation. At postinoculation months 3 to 4, latent PRV could be reactivated in vivo by the administration of large doses of corticosteroids. In most pigs, the stress-simulating treatment resulted in recrudescence of virus shedding after lag periods of 4 to 11 days. In 3 pigs, virus shedding was without clinical signs of disease, whereas clinical signs that developed in 4 pigs appeared to be due to the corticosteroid treatment, rather than to the reactivation of PRV. Pigs with a log10 neutralizing antibody titer of less than or equal to 2.55 at the onset of corticosteroid treatment had a booster response. Reactivated PRV spread to sentinel pigs housed with the inoculated pigs. Reactivation of PRV was also demonstrated in vitro. Explant cultures of trigeminal ganglia from pigs killed between postinoculation months 4 to 5 produced infectious virus. Restriction endonuclease analysis indicated that the reactivated PRV was indistinguishable from virus isolated shortly after the primary infection. Seemingly, pigs with maternal antibodies can become latently infected and therefore may be regarded as potential sources of dissemination of PRV.     

Lesions of transmissible gastroenteritis virus infection in experimentally inoculated pigs suckling immunized sows

Intestinal lesions of transmissible gastroenteritis (TGE) virus infection in conventionally reared pigs suckling either nonvaccinated, vaccinated, or previously infected sows were studied by scanning electron microscopy, light microscopy, and immunofluorescent microscopy for TGE viral antigen. Pigs were inoculated with virulent TGE virus when they were 5 or 21 days old and were euthanatized shortly after the onset of diarrhea or 96 hours after inoculation if no diarrhea developed. Pigs inoculated when they were either 5 or 21 days old and suckling nonvaccinated sows developed severe lesions, including swelling and necrosis of enterocytes and severe villus atrophy. Pigs inoculated when they were 5 days old and suckling sows vaccinated with attenuated vaccines developed less-severe villus atrophy, and those suckling sows immunized by exposure to nonattenuated TGE virus developed moderate or no villus atrophy. Pigs inoculated when they were 21 days old and suckling sows vaccinated with attenuated vaccines had severe villus atrophy, whereas those suckling sows immunized by exposure to nonattenuated virus had more-moderate villus lesions. Villus atrophy was inhibited to various degrees in pigs suckling immunized sows, depending in part on the antibody titer in the colostrum and milk.     

The correlation of virus-specific interferon-gamma production and protection against classical swine fever virus infection.

The level of antigen-specific interferon-gamma (IFN-gamma) production can be used as an indicator of cellular immunity. In this study, we investigated the role of cellular immune response in protection against classical swine fever virus (CSFV). Pigs were vaccinated once with CSFV vaccine and challenged 6 days post-vaccination (dpv). Vaccinated animals had significantly higher CSFV-specific IFN-gamma secreting cells than the unvaccinated pigs (p<0.05) at the time of challenge and were protected against CSFV infection, whereas the control pigs died within 14 days post-infection (dpi). In the second experiment, pigs were vaccinated once with either CSFV vaccine or CSFV vaccine combined with Aujeszky's disease (AD) vaccine and challenged at 140 dpv. All vaccinated pigs developed both CSFV-specific, cellular and antibody responses and were protected against CSFV infection. However, differences in cellular, but not antibody, responses were observed in the two vaccinated groups. The group vaccinated with CSFV vaccine developed a significantly higher number of CSFV-specific, IFN-gamma secreting cells (p<0.05), exhibited a shorter fever period and less pathological changes, when compared with the group vaccinated with the combined vaccine. The kinetics of IFN-gamma production, following challenge in the two vaccinated groups, were also different. Taken together, our results indicated that CSFV-specific, IFN-gamma production could be detected early after antigen exposure and correlated with protection against CSFV challenge. Our findings highlight the role of cellular immune responses in porcine anti-viral immunity.     

Detection of antibodies against porcine parvovirus nonstructural protein NS1 may distinguish between vaccinated and infected pigs

The humoral antibody response against the nonstructural protein NS1 and the structural protein VP2 of porcine parvovirus (PPV) was evaluated by immuno-peroxidase test (IPT) and enzyme linked immuno sorbent assay (ELISA) using recombinant PPV antigens. The coding sequence for NS1 and VP2 was inserted into the baculovirus Autographa californica nuclear polyhedrosis virus (AcNPV) genome resulting in two recombinant baculoviruses AcNPV-NS1 and AcNPV-VP2, respectively. Sf9 cells (Spodoptora frugidiperda) inoculated with AcNPV-NS1 producing recombinant nonstructural protein (rNS1) and AcNPV-VP2 producing recombinant virion protein (rVP2) were used in IPT and ELISA to analyse serum antibodies. Pigs vaccinated with an inactivated whole virus vaccine and experimentally infected pigs were studied. Significant titers against rVP2 were obtained in both vaccinated and infected pigs. Specific antibodies against rNS1 could only be detected in infected pigs and NS1 may in this way allow the specific detection of infected animals. Analysis of serum samples collected up to 18 days post infection (p.i.) from four pigs experimentally infected with PPV showed that antibodies against rNS1 and rVP2 could in all cases be detected on day 9 p.i. Two individual pigs were inoculated twice with PPV and the antibody response was followed 89 days after second inoculation. Serum antibodies against borth rVP2 and rNS1 could be detected for this period of time.     

The evaluation of a lectin-agarose based subunit vaccine and complementary diagnostic antigen for Aujeszky's disease (pseudorabies) in the pig

Eleven out of 25 pigs were immunized with a lectin-agarose based subunit vaccine for Aujeszky's disease (AD). The vaccine was prepared by extracting protective antigens from a non-ionic detergent (Triton-X-100) extract of AD virus-infected PK-la cells with Lens culinaris agglutinin immobilized on agarose beads. Two groups of 3 and 4 pigs received 2 doses of vaccine each containing 426 μg of adsorbed protein. Two groups of 2 pigs each received 2 vaccine doses containing either 23 or 33 μg of adsorbed protein. All vaccinated pigs survived a nasal challenge of 10^8.5 PFU of virulent AD virus while 13 out of 14 (93%) uninoculated controls died between Days 5 and 9 post challenge. This immunizing preparation qualified as a practical subunit vaccine because pigs were protected with relatively small amounts of protective antigen while at the same time remained free of detectable antibody to a complementary diagnostic antigen. This antigen was obtained in relatively pure form from the maintenance medium of virus-infected cells 4 h post-inoculation. In addition both high and low dose vaccinates failed to produce detectable antibody to at least one other antigen complex. The composition of Lens culinaris agglutinin (LCA) and Ricinus communis agglutinin (RCA)-purified AD viral antigen preparations were also compared by crossed immunoelectrophoretic techniques. Both preparations contained two antigen complexes and two individual antigens in common. Each preparation also contained its own unique antigen complex. The RCA purified antigen preparation also contained small quantities of a single antigen that was not detectable in the LCA antigen preparation.     

A double-protease-resistant variant of transmissible gastroenteritis virus and its ability to induce lactogenic immunity

A virus resistant to 2 major intestinal proteases (trypsin and alpha-chymotrypsin) was derived from the attenuated Purdue strain of transmissible gastroenteritis virus. Its enzymatic stability was confirmed, in vitro, by exposure to proteolytic enzymes and to porcine intestinal fluids. Vaccination of 5 seronegative pregnant sows with the variant virus by a series of 2 oral and 1 IM inoculations resulted in high titers of neutralizing antibody in serum and colostrum. The mean antibody titer in milk whey decreased 44-fold within 1 week after parturition. At 3 days of age, the 40 pigs delivered by these sows were challenge exposed orally with virulent transmissible gastroenteritis virus. Pigs nursing the 5 vaccinated sows underwent a relatively mild clinical course of illness. The average mortality of these 40 pigs was 33%. Thirty-six pigs which had been raised by 4 nonvaccinated sows had a more severe illness, greater daily weight loss, and higher mortality (92%).     

Antibody response of pseudorabies virus subunit-vaccinated pigs to viral nucleocapsid proteins following low-dose virus challenge of immunity

The antibody response to pseudorabies virus nucleocapsid proteins (NCP) was evaluated by the western immunoblot analysis before and after challenge of immunity by nasal inoculation of 10(2.3) plaque-forming units of virus in 10 pigs that had been vaccinated with pseudorabies virus envelope glycoproteins. Antibody to 5 NCP with molecular mass of 140, 63, 41, 34, and 23 kD was first detected in vaccinated and nonvaccinated pigs on day 14 after challenge of immunity. Antibody to 2 of the 5 NCP continued to be detected through day 113 in 9 of 10 vaccinated pigs. Beyond day 32, antibody to NCP was not detected in 1 vaccinated pig. The 23-, 34-, and 41-kD proteins were the most immunogenic. Antibody to each of these proteins was first detected on day 14 in 10, 10, and 8 pigs, respectively. Seven, 6, and 8 pigs, respectively, were antibody-positive for these proteins on day 113. The 140- and 63-kD proteins were the least immunogenic. Antibody to these proteins was detected in 8 and 9 pigs, respectively, on day 14, and in 4 and 5 pigs, respectively, on day 113. Chi-square analysis for dependency indicated that the antibody response to the 140- and 63-kD proteins was interdependent. These results suggested that combinations of NCP may be useful as nonvaccine diagnostic antigens.     

嵌合型猪圆环病毒（PCV1—2）及PCV2 ORF2真核表达质粒对商品猪的免疫保护

应用本实验室构建的嵌合型猪圆环病毒（PCV1—2）及真核表达质粒pcDNA3．1／V5-His-ORF2作为免疫原免疫母源抗体ELISA效价在0．07～0．60不等的商品猪,9头猪随机分为4组,1组（3头）肌肉注射免疫10^3.5 TCID50的PCV1-2／头,2组（2头）肌肉注射真核表达质粒200μg／头,3组（2头）肌肉注射空载体（pcDNA3．1）200μg／头,4组（2头）不免疫作为攻毒对照组。于免疫后42d,PCV1—2组及真核表达质粒组产生了PCV2抗体。免疫后42d所有组攻毒PCV2和PRRSV,剂量分别为2×10^4.5 TCID50／头和10^6 TCID50／头。攻毒后21d,攻毒对照组猪淋巴结比免疫组显著肿大,免疫组猪血清、淋巴结中PCV2病毒栽量低于对照组,攻毒对照组猪淋巴结中PCV2抗原含量高于免疫组。这些结果表明,嵌合型PCV1-2及真核表达质粒肌肉注射免疫商品猪后,对PCV2感染能产生保护性免疫应答,有可能成为候选疫苗。     

The effect of a killed porcine reproductive and respiratory syndrome virus (PRRSV) vaccine treatment on virus shedding in previously PRRSV infected pigs

Two experiments were conducted to investigate if virus shedding could be reduced following a killed porcine reproductive and respiratory syndrome virus (PRRSV) vaccination (KV) of PRRSV infected pigs. In experiment 1, PRRSV infected pigs were vaccinated with KV on days 14 and 28 following infection. Viremia and serum neutralizing (SN) antibody were compared to infected pigs with no KV. The second experiment was conducted in an identical manner. In addition to viremia and SN antibody, virus in oropharyngeal scrapings and interferon gamma (IFN-gamma) producing cells were monitored. Magnitude and duration of viremia were not different between KV vaccinated and non-vaccinated groups. No virus was detected in oropharyngeal scraping from any pig, nor was there a difference in the detection of viral RNA. In both experiments, however, increases in SN titer and number of IFN-gamma producing cells were observed. The SN titer was significantly higher in KV vaccinated groups than in non-vaccinated group on days 42 and 42-56 following infection in experiments 1 and 2, respectively. The number of IFN-gamma producing cells was slightly higher in KV vaccinated groups than in non-vaccinated group on days 42 and 63. These observations suggest that KV had no effect on virus shedding. However, previously infected pigs responded immunologically to KV, as demonstrated by increases in SN antibody titers and IFN-gamma producing cells.     

Study of immune function in inbred miniature pigs vaccinated and challenged with suid herpesvirus 1.

Specific immune responses of inbred miniature pigs following vaccination and challenge with suid herpesvirus 1 (SHV-1) were determined. Vaccination of swine with SHV-1 elicited both specific neutralizing antibody and lymphoproliferative responses. Moreover, pigs vaccinated with SHV-1 were fully protected against a lethal virus challenge. Pigs vaccinated with a recombinant (r) SHV-1 virus, followed by challenge with a virulent SHV-1, had lower percentages of circulating T- and B-lymphocytes, and showed a significant (P < or = 0.05) reduction in peripheral blood mononuclear cell (PBMC) antibody-dependent cell-cytotoxicity than control (noninfected, SHV-1 sero-negative) animals. From the 5th through the 8th week of postchallenge, rSHV-1 was isolated from 2 of 4 pigs. Presence of r-virus was indicative that PBMC were infectious in vivo. The rSHV-1, with beta-galactosidase activity, was only recovered from ConA- and IL-2-stimulated primary PBMC cocultivated with porcine kidney cells. Control pigs exposed to challenge SHV-1 elicited both specific neutralizing antibody and lympho-proliferative responses followed by subsequent infection. These infected pigs, compared to control pigs, had significantly (P < or = 0.05) lowered percentages of T- and B-lymphocytes, lowered T-cell mitogenic responses, variable PBMC counts, and lowered blood phagocytic cell function. When PBMC from control pigs were cultured and infected with SHV-1, the virus caused a significant (P < or = 0.05) suppression of T-cell proliferation and PBMC mitochondrial dehydrogenase and macrophage activities.     

Experimental infection of fattening pigs with pseudorabies (Aujeszky's disease) virus: efficacy of attenuated live- and inactivated-virus vaccines in pigs with or without passive immunity

The efficacies of attenuated live- and inactivated-virus vaccines against pseudorabies (PR) in fattening pigs were compared. Pigs born from vaccinated or nonvaccinated sows were vaccinated with one or the other vaccine and were challenge exposed at the end of the fattening period. The particular form of PR observed in fattening units in the field could be reproduced. A marked difference was seen between the control lot and the lots of the pigs vaccinated with the attenuated live- and inactivated-virus vaccines. The protection was real, but not absolute, in the vaccinated pigs. The inactivated-virus vaccine conferred a strong passive immunity to the young pigs of vaccinated dams which interfered with the development of an active immunity. The titer of the colostral antibodies in the sera of pigs born from the sows vaccinated with the attenuated-live virus vaccine was low and decreased rapidly. The active protection obtained with this vaccine was similar to that observed with the inactivated-virus vaccine. Thermal curves, weight losses, and time necessary for recovering the weight of pigs at the time of challenge exposure seemed to be good criteria for measuring the protection of fattening pigs against this particular form of PR. The conditions of the outcome of respiratory tract disorders in these pigs are discussed.     

Cross-protection studies between feline infectious peritonitis and porcine transmissible gastroenteritis viruses

Cross-protection studies between the feline infectious peritonitis (FIP) and the porcine transmissible gastroenteritis (TGE) viruses were conducted in cats, pigs and pregnant gilts. Cats vaccinated with TGE virus developed neutralizing antibodies against TGE virus and low titer antibody against FIP virus detected by an indirect fluorescent antibody technique but were not protected against a virulent FIP virus challenge. Baby pigs and pregnant gilts vaccinated with FIP virus did not develop detectable antibodies to TGE virus. Nevertheless, it appeared that vaccination of swine with FIP virus conferred some immunity against TGE virus infection. Seventeen-day-old pigs vaccinated with two doses of FIP virus had a 67% survival rate following a virulent TGE virus challenge, and 75% of the 3-day-old pigs suckling either FIP or TGE-virus-vaccinated gilts survived virulent TGE virus infection in contrast to 0% survival of baby pigs suckling unvaccinated gilts.     

Intranasal vaccination of pigs against Aujeszky's disease: comparison with one or two doses of attenuated vaccines in pigs with high maternal antibody titres

Ten-week-old pigs with high levels of maternally derived antibody (MDA) against Aujeszky's disease virus (ADV) were given either a single intranasal vaccination or one or two doses (with an interval of three weeks) of commercially available attenuated ADV vaccines intramuscularly. The pigs did not produce a clear neutralising antibody response to ADV. However, pigs vaccinated intranasally and pigs given two doses of attenuated ADV vaccines were protected against intranasal challenge with virulent ADV two months after the first vaccination. Pigs given one parenteral dose of attenuated ADV vaccine were insufficiently protected. Protection was shown by shorter periods of growth arrest and fever and a greater reduction of virulent virus shedding after challenge in vaccinated pigs than in unvaccinated control pigs. Although intranasal vaccination conferred protection comparable to two parenteral doses of attenuated vaccines, it reduced shedding of virulent virus much more effectively. These results, together with those of other studies, show that intranasal vaccination confers better protection against Aujeszky's disease in pigs with MDA than parenteral vaccination. However, the efficacy of intranasal vaccination also decreases with increasing levels of MDA at the time of vaccination.     

伪狂犬病基因缺失疫苗株(SA215)某些生物学特性研究

本试验测定了伪狂犬病ｇＥ－／ｇＩ－／ ＴＫ－／ ＬａｃＺ＋基因缺失疫苗株（ＳＡ２１５）的致细胞病变效应、安全性、免疫原性和免疫期等生物学特性。试验结果显示,该疫苗株能在Ｖｅｒｏ细胞上适应生长,并形成典型的蚀斑。其对１日龄仔猪、怀孕母猪、牛、羊以及家兔安全,无不良接种反应,接种动物不向体外散毒。ＳＡ２１５疫苗接种猪能抵御高剂量（１０７ＰＦＵ）Ｆａ株强毒感染,攻毒后试验猪的发热期、增重受阻天数、散毒滴度均低于Ｂａｒｔｈａ株疫苗接种猪,远远低于对照组猪。ＳＡ２１５接种猪能维持长时间的高水平中和抗体滴度,免疫期可达半年以上。试验结果表明,ＳＡ２１５株是一株安全、免疫原性好、免疫期长的疫苗株。     

Serum and mucosal antibody responses and protection in pigs vaccinated against Mycoplasma hyopneumoniae with vaccines containing a denatured membrane antigen pool and adjuvant

Objective To investigate the protective efficacy of a pool of denatured membrane protein antigens of Mycoplasma hyopneumoniae (J strain) in the molecular size range 70 to 85 kDa (F3 antigen) in combination with adjuvants for pigs challenged with M hyopneumoniae .
Design A vaccine efficacy experiment with assessment of serum and respiratory tract antibody responses.
Procedure F3 antigens were emulsified with five different adjuvants. To groups of three pigs per vaccine, four vaccines were given by intramuscular injection, and two vaccines, including one of those given intramuscularly, were given by intraperitoneal injection.
Results Compared to six unvaccinated pigs, animals vaccinated with F3 antigen displayed significantly reduced pneumonia (54% reduction in mean lung score) following experimental challenge. Analysis of post-vaccination, pre-challenge IgG and IgA ELISA antibody absorbances in serum and respiratory tract washings revealed no correlation with lung score. Six weeks after challenge, pigs previously vaccinated intramuscularly mostly demonstrated greater IgG and IgA responses in respiratory tract washings, and greater IgG serum antibody responses, than those vaccinated by intraperitoneal injection.
Conclusion Pigs vaccinated with M hyopneumoniae antigens in the molecular size range of 70 to 85 kDa showed a significant reduction in lung lesions compared with unvaccinated control animals after experimental challenge. IgG and IgA antibody concentrations in serum and respiratory tract washings after vaccination do not provide a useful prognostic indicator of protection from enzootic pneumonia.     

In vivo evaluation of vaccine efficacy against challenge with a contemporary field isolate from the α cluster of H1N1 swine influenza virus

Influenza A virus vaccines currently contain a mixture of isolates that reflect the genetic and antigenic characteristics of the currently circulating strains. This study was conducted to evaluate the efficacy of a trivalent inactivated swine influenza virus vaccine (Flusure XP) in pigs challenged with a contemporary α-cluster H1N1 field isolate of Canadian swine origin. Pigs were allocated to vaccinated, placebo, and negative-control groups and monitored for respiratory disease for 5 d after challenge. On the challenge day and 5 d after challenge the serum of the vaccinated pigs had reciprocal hemagglutination inhibition antibody titers 40 for all the vaccine viruses but ≤ 20 for the challenge virus. Gross lesions were present in the lungs of all pigs that had been inoculated with the challenge virus, but the proportion of lung tissue consolidated did not differ significantly between the placebo and vaccinated pigs. However, the amount of virus was significantly reduced in the nasal secretions, lungs, and bronchoalveolar lavage fluid in the vaccinated pigs compared with the placebo pigs. These results indicate that swine vaccinated with Flusure XP were partially protected against experimental challenge with a swine α-cluster H1N1 virus that is genetically similar to viruses currently circulating in Canadian swine.     

A comparison of the efficacy of two commercial Aujeszky's disease vaccines with glycoprotein-I deletion in pigs

Two commercial Aujeszky's disease vaccines, a modified killed vaccine and a sub-unit vaccine, both carrying a deletion of glycoprotein-I, were evaluated in pigs. Each vaccine was administered to two groups of four pigs, twice at 4-week intervals, with two pigs held as unvaccinated controls. All pigs were challenged with a New Zealand field isolate of Aujeszky's disease virus 3 weeks after the second vaccination. The results indicate that the sub-unit vaccine was able to protect pigs against clinical Aujeszky's disease much better than the pigs vaccinated with the modified killed vaccine when challenged with a virulent virus. However, the amount and the duration of virulent virus excretion following challenge was greater with the sub-unit vaccine than the modified killed vaccine. Pigs vaccinated with the sub-unit vaccine were shown to be latently infected following challenge. Latent infection was demonstrated by excretion of Aujeszky's disease virus from the nasal cavity after dexamethasone treatment and seroconversion of a sentinel in contact pigs to Aujeszky's disease virus.     

Overcoming maternal antibody interference by vaccination with human adenovirus 5 recombinant viruses expressing the hemagglutinin and the nucleoprotein of swine influenza virus

Sows and gilts lack immunity to human adenovirus 5 (Ad-5) vectored vaccines so immunogens of swine pathogens can be expressed with these vaccines in order to immunize suckling piglets that have interfering, maternally derived antibodies. In this study 7-day-old piglets, that had suckled H3N2 infected gilts, were sham-inoculated with a non-expressing Ad-5 vector or given a primary vaccination with replication-defective Ad-5 viruses expressed the H3 hemagglutinin and the nucleoprotein of swine influenza virus (SIV) subtype H3N2. The hemagglutination inhibition (HI) titer of the sham-inoculated group (n = 12) showed continued antibody decay whereas piglets vaccinated with Ad-5 SIV (n = 23) developed an active immune response by the second week post-vaccination. At 4 weeks-of-age when the HI titer of the sham-inoculated group had decayed to 45, the sham-inoculated group and half of the Ad-5 SIV vaccinated pigs were boosted with a commercial inactivated SIV vaccine. The boosted pigs that had been primed in the presence of maternal interfering antibodies had a strong anamnestic response while sham-inoculated pigs did not respond to the commercial vaccine. Two weeks after the booster vaccination the pigs were challenged with a non-homologous H3N2 virulent SIV. The efficacy of the vaccination protocol was demonstrated by abrogation of clinical signs, by clearance of challenge virus from pulmonary lavage fluids, by markedly reduced virus shedding in nasal secretions, and by the absence of moderate or severe SIV-induced lung lesions. These recombinant Ad-5 SIV vaccines are useful for priming the immune system to override the effects of maternally derived antibodies which interfere with conventional SIV vaccines.