Intranasal vaccination of pigs against Aujeszky's disease. 4. Comparison with one or two doses of an inactivated vaccine in pigs with moderate maternal antibody titres

Intranasal (IN) vaccination of pigs with low levels of maternally-derived antibody (MDA) has previously been shown to confer good protection against challenge with virulent Aujeszky's disease virus (ADV). The objective of the present study was to determine the efficacy of IN vaccination with an attenuated ADV, in comparison with that of an inactivated vaccine given parenterally, in pigs with higher MDA titres at the time of vaccination. In one experiment, vaccinations were done at 6 weeks of age, and in another experiment pigs were vaccinated at 4 and/or 9 weeks of age. Two months after (the last) vaccination pigs were challenged intranasally with a virulent ADV. Protection was evaluated on the basis of mortality, periods of growth arrest, fever and virus shedding after challenge. The presence of MDA markedly depressed the serum-neutralizing antibody response after vaccination. Sensitisation occurred after parenteral vaccination with an inactivated vaccine despite high MDA levels. Although the intranasally-vaccinated pigs had lower levels of neutralizing antibody at the time of challenge, they were significantly better protected than pigs given 1 or 2 doses of the inactivated vaccine. Comparing the present results with those of a previous study, it appears that the efficacy of parenteral as well as intranasal ADV vaccination decreases with increasing levels of MDA at the time of vaccination.     

Intranasal vaccination of pigs against Aujeszky's disease: comparison with inactivated vaccines in pigs with low maternal antibody titres

Intranasal vaccination with an attenuated Aujeszky's disease virus strain was compared with parenteral vaccination with two inactivated virus vaccines, in 10-week-old pigs with low levels of maternal antibody. Intranasal vaccination conferred a much better protection than parenteral vaccination with the two inactivated vaccines against challenge two months later, as evidenced by shorter periods of growth arrest and fever and a greater reduction of virulent virus shedding after challenge-exposure.     

Intranasal vaccination of pigs against Aujeszky's disease: protective immunity at 2 weeks, 2 months and 4 months after vaccination in pigs with maternal antibodies.

The purpose of the study was to evaluate the short- and long-term immunity after intranasal vaccination in pigs with maternally derived antibodies (MDA). In two experiments, 10-week-old pigs with moderate MDA titres against Aujeszky's disease virus (ADV) were vaccinated intranasally with the Bartha strain of ADV to evaluate the protective immunity conferred at 2 weeks, 2 months and 4 months after vaccination. Protection was evaluated on the basis of severity of clinical signs, periods of fever and growth arrest, and duration and amount of virus excreted after challenge with a virulent ADV. During the first 2-3 weeks after vaccination, antibodies to ADV continued to decline as in unvaccinated control pigs. After that, antibody titres stabilized or gradually increased. At 2 weeks, 2 months and 4 months after vaccination, vaccinated pigs were significantly better protected than unvaccinated controls. The vaccinated pigs challenged 2 weeks after vaccination hardly developed any sign of disease. Mild signs of Aujeszky's disease and a growth arrest period of 5 days were observed in vaccinated pigs challenged 2 months after vaccination, whereas vaccinated pigs challenged 4 months after vaccination developed severe signs of disease and a growth arrest period of 13 days. Vaccinated pigs challenged 2 weeks after vaccination did not excrete challenge virus, and pigs challenged 2 or 4 months after vaccination excreted far less virus than unvaccinated controls. The results demonstrate that intranasal ADV vaccination of pigs with moderate MDA titres protected them from 2 weeks to at least 4 months after vaccination. Immunity steadily declined, however, after vaccination.     

Vaccines against Aujeszky's disease: evaluation of their efficacy under standardized laboratory conditions

A standardized test was developed to compare the efficacy of Aujeszky's disease virus (ADV) vaccines under laboratory conditions. Per test 3 groups of 6 to 8 sero-negative pigs were used. The first vaccination was done at 10 weeks of age. One group was vaccinated once, another was vaccinated twice and the 3rd served as control. Pigs were challenge exposed to the virulent NIA-3 strain of ADV 12 weeks after the first vaccination. Apart from mortality, average periods of growth arrest, fever and virus shedding after challenge were used as parameters to evaluate vaccine efficacy. Two inactivated and 4 attenuated vaccines were tested. Two attenuated vaccine viruses were excreted after vaccination. Despite maximal standardization, a considerable variation still existed between the experiments in mortality and growth arrest periods of control pigs after challenge. However, the controls were always more severely affected than the vaccinated pigs. All vaccines except one were effective in preventing death after challenge, but none conferred complete protection. Most vaccinated pigs still lost weight, developed fever and shed virus after challenge. Revaccination after 3 or 4 weeks had little effect, particularly with the attenuated vaccines. The results of the present study indicate that 2 of the attenuated vaccines conferred the best protection, 1 attenuated vaccine appeared to be as effective as the 2 inactivated ones, and the 4th attenuated vaccine was least effective.     

Studies on immunisation of pigs with the Bartha strain of Aujeszky's disease virus.

The K strain of Aujeszky's disease virus (ADV) grown in Vero cells was used to vaccinate pigs. Following intramuscular inoculation, the pigs remained healthy, no vaccine virus was excreted and virus could be detected only at the inoculation site. One inoculation gave good protection against challenge with a virulent strain of ADV, and the amount of virulent ADV excreted was geatly curtailed. Following vaccination only low leads of serum neutralizing antibody were detected (geometric mean titre 1/2), but three weeks after challenge very high levels were found (GMT 1/1773). Intranasal vaccination gave similar results. There was minimal excretion of vaccine virus. The clinical reaction on challenge was less severe than in the intramuscularly challenged group, although lower antibody levels were detected three wekks following challenge (GMT 1/483). A field trial, using this strain given subcutaneously, indicated that one inoculation of this vaccine is effective.     

The effect of dose, route and virulence of bovine herpesvirus 1 vaccine on experimental respiratory disease in cattle.

Three experiments were conducted with calves in which, following intramuscular or intranasal vaccination with virulent or attenuated bovine herpesvirus 1, calves were protected against bovine herpesvirus 1 -- Pasteurella haemolytica challenge. Calves receiving low doses of vaccine had lower levels of antibody and greater evidence of virus replication upon challenge than those receiving higher doses. In contrast 11/13 unvaccinated controls had fibrino-purulent pneumonia following challenge. The immune response developed later in younger calves and those given low doses of vaccine. Neutralizing antibodies to bovine herpes-virus 1 were not found in nasal secretions, but were present in serum seven days after vaccination. Bovine herpesvirus 1 was isolated before challenge from nasal secretions of calves vaccinated intranasally or intramuscularly with virulent virus but not those vaccinated intramuscularly with vaccine virus. It was concluded that both routes of vaccination with either virulent or attenuated bovine herpesvirus 1 provided protection from challenge with homologous or heterologous bovine herpesvirus 1 and that live vaccines should contain at least 10(3) plaque forming units/dose for effective immunization.     

Induction of antibodies to glycoprotein I in pigs exposed to different doses of a mildly virulent strain of Aujeszky's disease virus

It has recently been shown that the antibody response to glycoprotein I (gI) of Aujeszky's disease virus can be used to distinguish infected from vaccinated pigs. To examine whether pigs exposed to low doses of a mildly virulent strain of Aujeszky's disease virus produce antibody to gI four groups of four pigs were inoculated intranasally with 10, 10(2), 10(3) or 10(4) plaque forming units (PFU) of the Sterksel strain. Two unvaccinated pigs and two pigs vaccinated intranasally with Bartha's K strain, a gI-negative vaccine, were placed in contact with each group. The pigs given 10 PFU and the in-contact pigs in this group did not become infected. The inoculated and the unvaccinated in-contact pigs in the other groups developed mild signs of illness and produced antibody to gI. Four of six vaccinated in-contact pigs that became infected showed neither clinical signs nor virus shedding and still produced antibody to gI. The other two vaccinated pigs appeared to be resistant to contact-challenge. The antibody response to gI persisted for at least seven months. These results support the idea that Aujeszky's disease virus may be eradicated by a programme based on vaccination with gI-negative vaccines, in conjunction with the detection and subsequent removal of gI-antibody positive, infected, pigs.     

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.     

Vaccines against Aujeszky's disease: Evaluation of their efficacy under standardized laboratory conditions

Summary

A standardized test was developed to compare the efficacy of Aujeszky's disease virus (ADV) vaccines under laboratory conditions. Per test 3 groups of 6 to 8 sero‐negative pigs were used. The first vaccination was done at 10 weeks of age. One group was vaccinated once, another was vaccinated twice and the 3rd served as control. Pigs were challenge exposed to the virulent NIA‐3 strain of ADV 12 weeks after the first vaccination. Apart from mortality, average periods of growth arrest, fever and virus shedding after challenge were used as parameters to evaluate vaccine efficacy.

Two inactivated and 4 attenuated vaccines were tested. Two attenuated vaccine viruses were excreted after vaccination. Despite maximal standardization, a considerable variation still existed between the experiments in mortality and growth arrest periods of control pigs after challenge. However, the controls were always more severely affected than the vaccinated pigs. All vaccines except one were effective in preventing death after challenge, but none conferred complete protection. Most vaccinated pigs still lost weight, developed fever and shed virus after challenge. Revaccination after 3 or 4 weeks had little effect, particularly with the attenuated vaccines. The results of the present study indicate that 2 of the attenuated vaccines conferred the best protection, I attenuated vaccine appeared to be as effective as the 2 inactivated ones, and the 4th attenuated vaccine was least effective.     

Immunogenicity in Aujeszky's disease virus structural glycoprotein gVI (gp50) in swine.

Aujeszky's disease virus (ADV) envelope glycoprotein gVI (gp50) was purified from virus-infected Vero cells by ion-exchange and immunoaffinity chromatography and its usefulness as a subunit vaccine was evaluated in active and passive immunization studies. Four-week-old piglets were immunized intramuscularly (IM) with purified gVI twice two weeks apart and challenged intranasally (IN) 10 days after the second immunization with 30 LD50 (10(8)PFU) of a virulent strain of ADV. Pigs, vaccinated with 100 micrograms of purified gVI, produced virus neutralizing antibodies and did not develop clinical signs after challenge exposure. The challenge virus was not isolated from nasal swabs and tonsils of gVI-vaccinated pigs, whereas non-vaccinated control pigs developed illness after challenge exposure with the same virulent ADV strain which was later recovered from their nasal swabs and tonsils. Pregnant sows vaccinated twice with purified gVI (IM) at a three week interval produced virus neutralizing antibodies in colostrum. Four-day-old sucking piglets born of vaccinated sows were passively protected by colostral antibodies against intranasal challenge with a lethal dose of virulent ADV. Sera from gVI-vaccinated pigs were distinguished from experimentally infected swine sera by their differential reactivity in enzyme-linked immunosorbent assay (ELISA) using four major viral glycoproteins (excluding gVI) as antigen purified by the use of lentil-lectin.     

Efficacy of an intranasal immunization with gEgC and gEgI double-deletion mutants of Aujeszky's disease virus in maternally immune pigs and the effects of a successive intramuscular booster with commercial vaccines

In this study, an intranasal immunization strategy was set up in maternally immune pigs in order to protect them not only clinically but also virologically. Two genetically engineered Aujeszky's disease virus (ADV) strains, Kaplan gE-gI- and Kaplan gE-gC-, were used for intranasal immunization. Both strains were safe for 4-week-old pigs. A single intranasal inoculation of 10(6.0) TCID50 of Kaplan gE-gI- and Kaplan gE-gC- at 4 weeks of age in the presence of moderate titres of maternally derived antibodies (SN titres: 12-16) reduced the amount of weight loss, fever and virus excretion upon challenge 6 weeks later. In a second experiment, the effect of an additional intramuscular booster with three different commercial vaccines (containing attenuated Bartha or NIA3-783 or inactivated Phylaxia; all suspended in an oil-in-water emulsion) at 10 weeks of age was evaluated. One month after the last intramuscular booster, between five and seven pigs from each group were selected for challenge. All intranasally/intramuscularly immunized pigs showed a significantly better clinical and virological protection after challenge than the single intranasally immunized pigs. In the double immunized group, the protection was better when Kaplan gE-gC- was used for the intranasal priming (only two of 14 pigs excreted virus with a duration of 4 days) than when Kaplan gE-gI- was used (13 of 18 pigs excreted virus with a duration ranging from 1 to 4 days). The virological protection was not influenced by the type of vaccine used for booster vaccination. Because the intranasal/intramuscular immunization approach is very compatible with current pig movements on farms and pigs with moderate levels of maternally derived antibodies can effectively be immunized, it can be considered as a good alternative to intramuscular/intramuscular vaccinations especially in regions with a high ADV prevalence.     

Level of virulent virus excreted by infected pigs previously vaccinated with different glycoprotein deleted Aujeszky's disease vaccines.

Seven deleted Aujeszky's disease vaccines were compared for their ability to induce an immunity which suppresses virus excretion. For each vaccine, the levels of clinical protection and viral excretion were compared. Groups of eight pigs were vaccinated twice with attenuated deleted Aujeszky's disease vaccines (which do not express certain glycoproteins: gI, gX or gp63). Pigs were vaccinated at the beginning of the fattening period and challenge took place at the end of it when the pigs were 18-19 weeks old. Live virus vaccines were suspended in water or in an oil-in-water emulsion. The experiment was performed in three successive assays of two groups of eight pigs (except three groups for the first assay). At each assay, a control unvaccinated group of eight pigs was added to compare the effects of challenge between vaccinated and unvaccinated animals. In total, 80 pigs were involved in this experiment. All the vaccinated pigs excreted virus from 3 to 9 d after challenge. However the level of viral excretion and the duration of the period of excretion were reduced after vaccination and especially, when oil-in-water emulsion was used. There were obvious differences between vaccines. With some vaccines, when the level of viral excretion was low, the level of clinical protection was high. However, in other cases, the level of clinical protection could be good despite a higher level of viral excretion. The seroneutralizing titres were significantly and inversely related to a low level of viral excretion but not to the level of clinical protection.     

Potency of an experimental DNA vaccine against Aujeszky's disease in pigs

Intradermal vaccination with plasmid DNA encoding envelope glycoprotein C (gC) of pseudorabies virus (PrV) conferred protection of pigs against Aujeszky's disease when challenged with strain 75V19, but proved to be inadequate for protection against the highly virulent strain NIA-3. To improve the performance of the DNA vaccine, animals were vaccinated intradermally with a combination of plasmids expressing PrV glycoproteins gB, gC, gD, or gE under control of the major immediate-early promotor/enhancer of human cytomegalovirus. 12.5 microg per plasmid were used per immunization of 5-week old piglets which were injected three times at biweekly intervals. Five out of six animals survived a lethal challenge with strain NIA-3 without exhibiting central nervous signs, whereas all the control animals succumbed to the disease. This result shows the increased protection afforded by administration of the plasmid mixture over vaccination with a gC expressing plasmid alone. A comparative trial was performed using commercially available inactivated and modified-live vaccines and a mixture of plasmids expressing gB, gC, and gD. gE was omitted to conform with current eradication strategies based on gE-deleted vaccines. All six animals vaccinated with the live vaccine survived the lethal NIA-3 challenge without showing severe clinical signs. In contrast, five of six animals immunized with the inactivated vaccine died, as did two non-vaccinated controls. In this test, three of six animals vaccinated with the DNA vaccine survived without severe clinical signs, whereas three succumbed to the disease. Comparing weight reduction and virus excretion, the DNA vaccine also ranged between the inactivated and modified-live vaccines. Thus, administration of DNA constructs expressing different PrV glycoproteins was superior to an adjuvanted inactivated vaccine but less effective than an attenuated live vaccine in protection of pigs against PrV infection. Our data suggest a potential use of DNA vaccination in circumstances which do not allow administration of live attenuated vaccines.     

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.     

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.     

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.     

Evaluation of killed and modified live porcine rotavirus vaccines in cesarean derived colostrum deprived pigs

Twenty-eight cesarean derived, colostrum deprived (CDCD) piglets were used to evaluate the efficacy of killed and modified live rotavirus (MLV) vaccines against challenge with virulent A-1 and A-2 rotaviruses. Two killed rotavirus vaccines were evaluated: an experimental vaccine and a commercially available vaccine. Efficacy parameters included: average daily weight gains, rotavirus shedding in feces, morbidity incidence and duration, and rotavirus serum antibody conversion post-vaccination and post-challenge. Piglets vaccinated orally/intramuscularly with the modified live vaccine were completely protected from A-1 and A-2 virulent rotavirus challenge. Nonvaccinated control piglets and piglets receiving killed rotavirus vaccines developed diarrhea, shed virus and exhibited reduced weight gains post-challenge. Only the MLV rotavirus vaccine was able to prevent virus shedding in feces after virulent challenge. Both controls and pigs which received killed vaccines intraperitoneally, orally or intramuscularly shed virus in the feces for 7 days post-challenge and virus peak titers approached 10(7) fluorescent antibody infectious dose (FAID)50/g feces. These studies clearly reflected the inability of killed rotavirus vaccines to induce active local immunity to rotaviral diarrhea in piglets.     

Vaccine genotype and route of administration affect pseudorabies field virus latency load after challenge

The influence of vaccine genotype and route of administration on the efficacy of pseudorabies virus (PRV) vaccines against virulent PRV challenge was evaluated in a controlled experiment using five genotypically distinct modified live vaccines (MLVs) for PRV. Several of these MLVs share deletions in specific genes, however, each has its deletion in a different locus within that gene. Pigs were vaccinated with each vaccine, either via the intramuscular or intranasal route, and subsequently challenged with a highly virulent PRV field strain. During a 2-week period following challenge with virulent PRV, each of the vaccine strains used in this study was evaluated for its effectiveness in the reduction of clinical signs, prevention of growth retardation and virulent virus shedding. One month after challenge, tissues were collected and analyzed for virulent PRV latency load by a recently developed method for the electrochemiluminescent quantitation of latent herpesvirus DNA in animal tissues after PCR amplification. It was determined that all vaccination protocols provided protection against clinical signs resulting from field virus challenge and reduced both field virus shedding and latency load after field virus challenge. Our results indicated that vaccine efficacy was significantly influenced by the modified live vaccine strain and route of administration. Compared to unvaccinated pigs, vaccination reduced field virus latency load in trigeminal ganglia, but significant differences were found between vaccines and routes of administration. We conclude that vaccine genotype plays a role in the effectiveness of PRV MLVs.     

Effect of experimental infection with pseudorabies (Aujeszky's disease) virus on pigs with maternal immunity from vaccinated sows.

Live-virus and inactivated-virus vaccines were used to immunize sows against pseudorabies (Aujeszky's disease) virus. To test the efficacy of the vaccination, 53 pigs of different ages were taken from the 1st and the 2nd litters of vaccinated sows and placed separately in isolation units. The pigs were challenge exposed with virulent pseudorabies virus and examined for clinical signs, virus excretion, and serologic reaction. The challenge inoculum caused severe nervous or respiratory signs of disease in 12 of the 13 control pigs, with a mortality of 76%. The pigs from the 1st litters of sows vaccinated with the live-virus vaccine did not become sick, whereas 2 of the 9 pigs (22%) from the 2nd litters had clinical signs and died of pseudorabies. All pigs from sows vaccinated with the inactivated-virus vaccine remained healthy. The results of virus isolation from oronasal swabs, combined with the serotest results, indicated that challenge exposure of all except 1 of the pigs resulted in a subclinical infection with the formation of active immunity.     

Effects of DNA dose,route of vaccination,and coadministration of porcine interleukin-6 DNA on results of DNA vaccination against influenza virus infection in pigs

OBJECTIVE: To examine the effects of DNA dose, site of vaccination, and coadministration of a cytokine DNA adjuvant on efficacy of H1-subtype swine influenza virus hemagglutinin (HA) DNA vaccination of pigs. ANIMALS: 24 eight-week-old mixed-breed pigs. PROCEDURE: 2 doses of DNA were administered 27 days apart by use of a particle-mediated delivery system (gene gun). Different doses of HA DNA and different sites of DNA administration (skin, tongue) were studied, as was coadministration of porcine interleukin-6 (pIL-6) DNA as an adjuvant. Concentrations of virus-specific serum and nasal mucosal antibodies were measured throughout the experiment, and protective immunity was assessed after intranasal challenge with homologous H1N1 swine influenza virus. RESULTS: Increasing the dose of HA DNA, but not coadministration of pIL6 DNA, significantly enhanced virus-specific serum antibody responses. Pigs that received DNA on the ventral surface of the tongue stopped shedding virus 1 day sooner than pigs vaccinated in the skin of the ventral portion of the abdomen, but none of the vaccinated pigs developed detectable virus-specific antibodies in nasal secretions prior to challenge, nor were they protected from challenge exposure. Vaccinated pigs developed high virus-specific antibody concentrations after exposure to the challenge virus. CONCLUSIONS AND CLINICAL RELEVANCE: Co-administration of pIL-6 DNA did not significantly enhance immune responses to HA DNA vaccination or protection from challenge exposure. However, HA DNA vaccination of pigs, with or without coadministration of pIL-6 DNA, induced strong priming of the humoral immune system.