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1.
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.  相似文献   

2.
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.  相似文献   

3.
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.  相似文献   

4.
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.  相似文献   

5.
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.  相似文献   

6.
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.  相似文献   

7.
A modified-live intranasal (IN) canine parainfluenza (CPI)-virus Bordetella bronchiseptica vaccine was evaluated in dogs for efficacy against laboratory-induced canine infectious tracheobronchitis. The comparative efficacies of IN and parenteral administrations of the CPI virus fraction were also evaluated. The frequency and duration of clinical tracheobronchitis, blood serum agglutination titer, humoral antibody response, and duration of CPI virus and B bronchiseptica shedding were measured. Group A dogs were vaccinated subcutaneously or IM with an experimental CPI vaccine and challenge exposed with CPI virus. Group B dogs were vaccinated IN with avirulent CPI virus-B bronchiseptica live antigens and challenge exposed with virulent CPI virus and virulent B bronchiseptica. The IN vaccination (group B) significantly reduced (P less than or equal to 0.001) the occurrence of clinical tracheobronchitis by 96%. The combined challenge exposure of virulent CPI and virulent B bronchiseptica produced a synergistic enhancement of the clinical signs of kennel cough. The percentage of days after challenge exposure that virus shedding was detected for controls equaled 70% as compared with 50% and only 1% for parenterally and IN vaccinated dogs, respectively. Isolation of virulent B bronchiseptica microorganisms was reduced 89% in dogs vaccinated IN compared to controls. The geometric mean humoral antibody titers to CPI virus after 2 parenteral vaccinations and 1 IN vaccination were 1:43 and 1:34, respectively.  相似文献   

8.
This study investigated the efficacy of a bivalent swine influenza virus (SIV) vaccine in piglets challenged with a heterologous H1N1 SIV isolate. The ability of maternally derived antibodies (MDA) to provide protection against a heterologous challenge and the impact MDA have on vaccine efficacy were also evaluated. Forty-eight MDA(+) pigs and 48 MDA(-) pigs were assigned to 8 different groups. Vaccinated pigs received two doses of a bivalent SIV vaccine at 3 and 5 weeks of age. The infected pigs were challenged at 7 weeks of age with an H1N1 SIV strain heterologous to the H1N1 vaccine strain. Clinical signs, rectal temperature, macroscopic and microscopic lesions, virus excretion, serum and local antibody responses, and influenza-specific T-cell responses were measured. The bivalent SIV vaccine induced a high serum hemagglutination-inhibition (HI) antibody titer against the vaccine virus, but antibodies cross-reacted at a lower level to the challenge virus. This study determined that low serum HI antibodies to a challenge virus induced by vaccination with a heterologous virus provided protection demonstrated by clinical protection and reduced pneumonia and viral excretion. The vaccine was able to prime the local SIV-specific antibody response in the lower respiratory tract as well as inducing a systemic SIV-specific memory T-cell response. MDA alone were capable of suppressing fever subsequent to infection, but other parameters showed reduced protection against infection compared to vaccination. The presence of MDA at vaccination negatively impacted vaccine efficacy as fever and clinical signs were prolonged, and unexpectedly, SIV-induced pneumonia was increased compared to pigs vaccinated in the absence of MDA. MDA also suppressed the serum antibody response and the induction of SIV-specific memory T-cells following vaccination. The results of this study question the effectiveness of the current practice of generating increased MDA levels through sow vaccination in protecting piglets against disease.  相似文献   

9.
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.  相似文献   

10.
We examined primary and memory isotype-specific antibody responses directed against pseudorabies virus in serum and mucosal fluids of pigs with and without passively acquired maternal antibody, and we studied the relationship between these responses and protection against virus challenge. Pigs were inoculated intranasally with the virulent NIA-3 strain or the avirulent Bartha strain, or they were inoculated IM with an inactivated vaccine containing the Phylaxia strain. Ten weeks later, all pigs were challenge-exposed intranasally with strain NIA-3. Only pigs that were without passively acquired antibody at the time they were inoculated with virulent virus appeared to have complete protective immunity against challenge exposure, as evidenced by lack of clinical signs of pseudorabies and lack of virus excretion. In contrast, pigs inoculated with strain Bartha or with the inactivated vaccine developed fever, had a period of growth arrest, and excreted virus after challenge exposure. In pigs without passively acquired antibody, intranasal inoculation with strains NIA-3 or Bartha was followed by primary IgM and IgA responses in serum and in oropharyngeal fluid as well as primary IgG1 and IgG2 responses in serum. Intramuscular inoculation with the inactivated vaccine induced primary serum IgM, IgG1, and IgG2 responses, but no mucosal responses. Challenge exposure of pigs that had been inoculated with the Bartha strain or the inactivated vaccine was followed by clear memory responses in serum and in oropharyngeal fluid. In contrast, challenge exposure of pigs that had been inoculated by the virulent NIA-3 strain was not followed by memory responses.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

11.
Evaluation in swine of a subunit vaccine against pseudorabies   总被引：2，自引：0，他引：2  
A subunit vaccine against pseudorabies virus (PRV) was prepared by treating a mixture of pelleted virions and infected cells with the nonionic detergent Nonidet P-40 and emulsifying the extracted proteins incomplete Freund's adjuvant. Three 7-week-old pigs without antibodies against PRV were given 2 IM doses of this vaccine 3 weeks apart. Thirty days after the 2nd vaccination, 10(6) median tissue culture infective doses (TCID50) of a virulent strain of PRV were administered intranasally. Tonsillar and nasal swabs were collected daily between 2 and 10 days after challenge exposure. The pigs vaccinated with the subunit vaccine were not found to shed virulent PRV. Two groups of five 7-week-old pigs vaccinated with commercially available vaccines, either live-modified or inactivated virus, and subsequently exposed to 10(6) TCID50 of virulent PRV, shed virulent virus for up to 8 days. The subunit vaccine induced significantly higher virus-neutralizing antibody titers than either the live-modified or inactivated virus vaccine.  相似文献   

12.
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.  相似文献   

13.
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.  相似文献   

14.
We compared 3 modified-live pseudorabies virus (PRV) vaccine strains, administered by the intranasal (IN) or IM routes to 4- to 6-week-old pigs, to determine the effect of high- and low-challenge doses in these vaccinated pigs. At the time of vaccination, all pigs had passively acquired antibodies to PRV. Four experiments were conducted. Four weeks after vaccination, pigs were challenge-exposed IN with virulent virus strain Iowa S62. In experiments 1 and 2, a high challenge exposure dose (10(5.3) TCID50) was used, whereas in experiments 3 and 4, a lower challenge exposure dose (10(2.8) TCID50) was used. This low dose was believed to better simulate field conditions. After challenge exposure, pigs were evaluated for clinical signs of disease, weight gain, serologic response, and viral shedding. When vaccinated pigs were challenge-exposed with a high dose of PRV, the duration of viral shedding was significantly (P less than 0.05) lower, and body weight gain was greater in vaccinated pigs, compared with nonvaccinated challenge-exposed pigs. Pigs vaccinated IN shed PRV for fewer days than pigs vaccinated IM, but this difference was not significant. When vaccinated pigs were challenge-exposed with a low dose, significantly (P less than 0.05) fewer pigs vaccinated IN (51%) shed PRV, compared with pigs vaccinated IM (77%), or nonvaccinated pigs (94%). Additionally, the duration of viral shedding was significantly (P less than 0.05) shorter in pigs vaccinated IN, compared with pigs vaccinated IM or nonvaccinated pigs. The high challenge exposure dose of PRV may have overwhelmed the local immune response and diminished the advantages of the IN route of vaccination.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

15.
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.  相似文献   

16.
OBJECTIVE: To determine the immunogenicity and efficacy of Brucella abortus strain RB51 (SRB51) as a vaccine in domestic pigs. ANIMALS: Sixty-eight 6-week-old crossbred domestic pigs and twenty-four 4-month-old gilts. PROCEDURES: In experiment 1, pigs were vaccinated IM (n = 51) with 2 x 10(10) CFUs of SRB51 or sham inoculated (17). Periodic blood samples were obtained to perform blood cultures, serologic evaluations, and cell-mediated immunity assays. Necropsies were performed at selected times between weeks 1 and 23 after vaccination to determine vaccine clearance. In experiment 2, gilts were similarly vaccinated (n = 18) or sham inoculated (8) and similar samples were obtained after vaccination. Gilts were bred and challenged conjunctivally with 5.0 x 10(7) CFUs of virulent Brucella suis strain 3B. Necropsies were performed on gilts and on fetuses or neonates after abortion or parturition, respectively. Bacterial cultures and serologic evaluations were performed on samples obtained at necropsy to determine vaccine efficacy. RESULTS: Humoral and cell-mediated immune responses did not differ between vaccinates and controls. After vaccination, SRB51 was not isolated from blood cultures of either group and was isolated from lymphoid tissues of 3 pigs at 2 weeks (n = 2) and 4 weeks (1) after vaccination. No differences were found in isolation of B suis or in seroconversion between vaccinated and control gilts and between their neonates or aborted fetuses. CONCLUSIONS AND CLINICAL RElEVANCE: Parenteral vaccination with SRB51 does not induce humoral or cell-mediated immune responses. Vaccination with SRB51 did not protect gilts or their neonates and fetuses from virulent challenge with B suis.  相似文献   

17.
OBJECTIVE: To evaluate duration of immunity in cats vaccinated with an inactivated vaccine of feline panleukopenia virus (FPV), feline herpesvirus (FHV), and feline calicivirus (FCV). ANIMALS: 17 cats. PROCEDURE: Immunity of 9 vaccinated and 8 unvaccinated cats (of an original 15 vaccinated and 17 unvaccinated cats) was challenged 7.5 years after vaccination. Specific-pathogen-free (SPF) cats were vaccinated at 8 and 12 weeks old and housed in isolation facilities. Offspring of vaccinated cats served as unvaccinated contact control cats. Virus neutralization tests were used to determine antibody titers yearly. Clinical responses were recorded, and titers were determined weekly after viral challenge. RESULTS: Control cats remained free of antibodies against FPV, FHV, and FCV and did not have infection before viral challenge. Vaccinated cats had high FPV titers throughout the study and solid protection against virulent FPV 7.5 years after vaccination. Vaccinated cats were seropositive against FHV and FCV for 3 to 4 years after vaccination, with gradually declining titers. Vaccinated cats were protected partially against viral challenge with virulent FHV. Relative efficacy of the vaccine, on the basis of reduction of clinical signs of disease, was 52%. Results were similar after FCV challenge, with relative efficacy of 63%. Vaccination did not prevent local mild infection or shedding of FHV or FCV. CONCLUSIONS: Duration of immunity after vaccination with an inactivated, adjuvanted vaccine was > 7 years. Protection against FPV was better than for FHV and FCV. CLINICAL IMPLICATIONS: Persistence of antibody titers against all 3 viruses for > 3 years supports recommendations that cats may be revaccinated against FPV-FHV-FCV at 3-year intervals.  相似文献   

18.
Groups of pigs from vaccinated and unvaccinated sows were vaccinated once or twice between the ages of eight and 20 weeks with a commercial inactivated, oil adjuvanted Aujeszky's disease virus vaccine. Pigs were challenged by the oronasal route when 22 to 27 weeks old. Pigs from unvaccinated sows developed neutralising antibodies after vaccination but no seroconversion was detected in eight-week-old pigs or in 80 per cent of 15-week-old pigs from vaccinated sows. Challenge resulted in severe disease and weight loss in control pigs. In vaccinated animals the duration and severity of clinical signs and the amount of weight lost decreased with increasing serum neutralisation titres. The results indicate that parenteral vaccination at weaning with the vaccine described will not protect pigs at slaughter age against infection and disease, particularly if they were born from seropositive mothers.  相似文献   

19.
The avirulent Bartha's K strain of pseudorabies virus (PRV) was used to vaccinate 8 pigs at 10 weeks of age by the intransal route (experiment 1). On postvaccination days (PVD) 63 and 91, pigs were treated with corticosteroids. Viral shedding could not be detected. Explant cultures of trigeminal ganglia and tonsils did not produce virus. Four pigs with maternal antibody were vaccinated intranasally with Bartha's (attenuated) K strain of PRV at 10 weeks of age and were challenge exposed with a virulent strain of PRV on PVD 63 (experiment 2). Corticosteroid treatment, starting on postchallenge exposure day 70 (PVD 133) resulted in viral shedding in 1 of 4 pigs. In another pig of these 4, a 2nd corticosteroid treatment was required to trigger reactivation. In both pigs, sufficient reactivated virus was excreted to infect susceptible sentinel pigs. Restriction endonuclease analysis indicated that viruses isolated from the 2 pigs after challenge exposure and corticosteroid treatment were indistinguishable from the virulent virus. Evidence was not obtained for simultaneous excretion of vaccinal and virulent virus. Of 4 pigs without maternal antibody vaccinated twice with 1 of 2 inactivated PRV vaccines, challenge exposed on PVD 84, and treated with corticosteroids on postchallenge exposure day 63 (PVD 147), 1 was latently infected, as evidenced by the shedding of PRV (experiment 3). However, its sentinel pig remained noninfected.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

20.
A latent pseudorabies virus infection was established in pigs despite vaccination with a modified-live pseudorabies virus vaccine. Although the vaccinated pigs developed high concentrations of antibody, virus was recovered from the tonsils and lungs of pigs treated with dexamethasone three months after inoculation with virulent virus. These results may explain why vaccination programs have failed to eliminate the persistence and spread of virulent pseudorabies virus in infected herds.  相似文献   

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