A cross-protection experiment in pigs vaccinated with Haemophilus parasuis serovars 2 and 5 bacterins, and evaluation of a bivalent vaccine under laboratory and field conditions.

Cross-protection between Haemophilus parasuis serovars 2 and 5 was examined in pigs using a bacterin based vaccine, and subsequently the safety and efficacy of a bivalent vaccine were evaluated. Upon intratracheal challenge of a serovar 2 or 5 strain, pigs immunized with a monovalent vaccine were protected against challenge with a homologous serovar strain, but not with a heterologous serovar strain. Immunization with a bivalent vaccine containing both serovars 2 and 5 bacterins conferred protection in pigs against lethal challenge with each of the serovar strains. A total of 86 pigs from two SPF herds were injected with the bivalent vaccine intramuscularly twice at a four-week interval. No adverse reactions following the vaccination were observed. On day 7 after the second vaccination, vaccinated and non-vaccinated control pigs from herd A were transferred to herd B, where Glasser's disease had broken out. Pigs in the control group developed clinical signs of the disease, and 6 of 8 (75%) pigs died until slaughter, in contrast with only 4 of 46 (9%) pigs in the vaccinated group. In herd C, where there was no outbreak of Glasser's disease, complement fixation antibody titer was raised only in the vaccinated group. A challenge experiment on days 20 and 79 after the second vaccination showed that only the vaccinated pigs were protected. From these findings, the safety and efficacy of the bivalent vaccine were confirmed under laboratory and field conditions.     

Ovine campylobacterosis: preliminary studies of the efficacy of the in vitro serum bactericidal test as an assay for the potency of Campylobacter (Vibrio) fetus subsp intestinalis bacterins.

An in vitro serum bactericidal test was developed to assess the efficacy of Campylobacter fetus bacterins. Four experimental monovalent bacterins (either serotype C or A-2) and 2 commercial bivalent bacterins (a "suspect" and an "efficacious" bacterin) with aluminum hydroxide adjuvant were administered to sheep and rabbits from which antiserums were then prepared. The different vaccines were evaluated by comparing the in vitro bactericidal activity of the sheep and rabbit antiserums. Results of the in vitro tests were compared to the protection induced in vaccinated ewes which were orally exposed to C fetus. The sheep and the rabbit antiserums after they were heated at 56 C for 30 minutes were unable to exert a killing effect on C fetus cells. Addition of a fresh homologous complement source to the heated antiserums was necessary to demonstrate the in vitro bactericidal capacity. In the comparison of the suspect and the efficacious commercial bacterins, which both reportedly contain serotype C cells, there was a statistically significant difference in bactericidal activities for serotype C cells of antiserums from sheep 14 days after the 2nd vaccination. There was a corresponding significant difference in the antiserums from rabbits 14 days after the 2nd vaccination. Proportionally, more abortions and stillbirths were observed in the ewes vaccinated with the suspect bacterin and then orally exposed to C fetus-serotype C cells than in those vaccinated with the efficacious bacterin. The results indicated that the ability of vaccinated sheep to overcome infection is reflected in the in vitro bactericidal capacity of antiserum from the animal. Since 89% of the variation in sheep antiserums from 14 days after 2nd vaccination can be accounted for by rabbit antiserums from 14 days after 2nd vaccination, the in vitro bactericidal capacity of rabbit antiserums probably provides a reliable index of the protective effect of bacterins containing serotype C for ewes exposed to the homologous serotype.     

Specificity in response of vaccinated swine and mice to challenge exposure with strains of Erysipelothrix rhusiopathiae of various serotypes.

Swine and mice were vaccinated with standard erysipelas adsorbate bacterins made from Erysipelothrix rhusiopathiae of serotype 2 and were subsequently exposed to pathogenic strains of E rhusiopathiae, serotypes 1, 2, 4, 9, 10, and 11. Response to challenge of immunity in swine was determined by presence of urticarial lesions at the sites of intradermal injection of culture; response in mice was determined by the quantal (live-dead) method. After vaccination with standard bacterins, swine and mice were significantly more susceptible (P less than of equal to 0.01) to infection with strains of serotypes 9 and 10 than with strains of serotypes 1, 2, 4, or 11. An adsorbate bacterin made from the challenge strain of serotype 10 induced specific immunity to homologous challenge exposure in swine but not in mice. Bacterins made from the other challenge strains induced little or no immunity.     

Effect of endobronchial challenge with Actinobacillus pleuropneumoniae serotype 10 of pigs vaccinated with bacterins consisting of A. pleuropneumoniae serotype 10 grown under NAD-rich and NAD-restricted conditions

The efficacy of two bacterins containing an Actinobacillus pleuropneumoniae serotype 10 strain was evaluated. The bacterial cells constituting bacterin 1 and 2 were grown under nicotinamide adenine dinucleotide (NAD)-rich (low-adherence capacity to alveolar epithelial cell cultures) and NAD-restricted (high-adherence capacity to alveolar epithelial cell cultures) conditions, respectively. Ten pigs were vaccinated twice with the bacterin 1 and nine pigs with the bacterin 2. Ten control animals were injected twice with a saline solution. Three weeks after the second vaccination, all pigs were endobronchially inoculated with 106.5 colony-forming units (CFU) of an A. pleuropneumoniae serotype 10 strain. In the bacterin 1 and 2 group, three and two pigs died after inoculation, respectively. Only two pigs of the control group survived challenge. Surviving pigs were killed at 7 days after challenge. The percentage of pigs with severe lung lesions (> 10% of the lung affected) was 100% in the control group, 70% in the bacterin 1 group and 22% in the bacterin 2 group. Actinobacillus pleuropneumoniae was isolated from the lungs of all animals. The mean bacterial titres of the caudal lung lobes were 7.0 x 10(6) CFU/g in the control group, 6.3 x 10(5) CFU/g in the bacterin 1 group and 1.3 x 10(6) CFU/g in the bacterin 2 group. It was concluded that both bacterins induced partial protection against severe challenge. Furthermore, there are indications that the bacterin 2, containing A. pleuropneumoniae bacteria grown under conditions resulting in high in vitro adhesin, induced better protection than the bacterin 1.     

Protective effect of Clostridium septicum alpha-toxoid vaccine against challenge with spores in guinea pigs

The protective effect of an alpha-toxoid vaccine of Clostridium septicum purified alpha-toxin was investigated in guinea pigs. Purified alpha-toxin was treated with formalin to make toxoid, and alpha-toxoid vaccine was prepared by mixing alpha-toxoid (4 to 64 microg/dose) with an aluminum phosphate gel as adjuvant. Guinea pigs were immunized twice with different doses of alpha-toxoid vaccine, and challenged with spores of C. septicum. The guinea pigs surviving after challenge had been immunized with 8 microg/dose or more of alpha-toxoid. All these animals produced titers of 20 units or higher of antitoxin at the challenge. The results suggest that C. septicum alpha-toxin plays an important role in protection against challenge with spores in guinea pigs.     

The effects of challenge on the humoral and cellular immune responses in pseudorabies vaccinated swine.

The effects of challenge exposure on the humoral and cellular immune responses in pseudorabies vaccinated swine were studied in 84 barrows. The pigs were divided into seven groups and challenge exposed to a virulent strain of pseudorabies virus on months 1, 3, 5, 8, 10, 12 and 14 after vaccination. The pigs were vaccinated with commercial attenuated and inactivated pseudorabies virus vaccines. The protection conferred by vaccination was equally effective with both types of vaccines. The levels of cellular and humoral immunity after challenge exposure in pigs vaccinated with either type of vaccine were similar. The cell-mediated immune response can be effectively used for the early detection of pigs exposed to pseudorabies virus. Virus isolation attempts from the brain and spleen in most of the vaccinated pigs were unsuccessful.     

Evaluation of the antibody response in pigs vaccinated against Streptococcus suis capsular type 2 using a double-antibody sandwich enzyme-linked immunosorbent assay.

A double-antibody sandwich enzyme-linked immunosorbent assay (ELISA) was standardized for the detection of specific antibodies following vaccination with Streptococcus suis capsular type 2 bacterins. No statistically significant increase of antibody titers was detected in vaccinated piglets compared to the nonvaccinated control group, even if a minority of piglets demonstrated an important postvaccinal response. Three of four vaccinated sows showed a low antibody response to vaccine and specific immunity was detected in piglets of only one litter of these three sows. Passive protection studies showed that none of the sera from vaccinated piglets were protective for mice whereas serum obtained from hyperimmunized pigs gave protection.     

Classical swine fever (CSF) marker vaccine. Trial I. Challenge studies in weaner pigs

Two commercial marker vaccines against classical swine fever virus (CSFV) and companion diagnostic tests were examined in 160 conventional pigs. To test the vaccines in a "worst case scenario", group of 10 weaners were vaccinated using a single dose of an E2 (gp55) based vaccine at days -21, -14, -10 or -7, and subsequently challenged at day 0. The challenge virus was CSFV 277, originating from a recent outbreak of classical swine fever (CSF) in Germany. In all groups, only 5 out of 10 pigs were challenged; the remaining 5 pigs served as vaccinated contact controls. Also, three control groups, each consisting of 10 non-vaccinated pigs, were challenged in parallel to the vaccinated animals. CSFV could be isolated from all non-vaccinated pigs. Among these pigs 40% displayed a chronic course of the infection (virus positive for more than 10 days). Pigs vaccinated 21 or 14 days before challenge displayed no clinical signs of CSFV after challenge. However, they were still able to replicate CSFV when challenged, as measured by reisolation of CSFV from leukocytes of the directly challenged pigs. CSFV could be isolated from the leucocytes of 25% of the pigs vaccinated 21 days before challenge and 50% of the pigs vaccinated 14 days before challenge. Chronic infection was not observed, but transmission to one vaccinated contact pig occurred. From all pigs vaccinated 10 or 7 days before challenge, CSFV could be reisolated. We observed a chronic course of infection in 5% of pigs vaccinated 10 days before challenge and in 30% of pigs vaccinated 7 days before challenge. The mortality rate was 20% in the pigs vaccinated 10 days before challenge, and varied between 20 and 80% in pigs vaccinated 7 days prior to challenge. The contact animals had lower mortality (0-20%) than directly challenged pigs, probably mirroring the delayed time point of infection. There was thus some protection against clinical illness by both marker vaccines, but not a solid protection against infection and virus shedding. The efficacy of the vaccine was best if used 3 weeks before challenge and a clear correlation between time interval from vaccination to challenge and the level of virus shedding was observed. Each vaccine had its own accompanying discriminatory ELISA, but 18% of the virus positive pigs never seroconverted in these tests.     

Effect of vaccination with live or killed Pasteurella haemolytica on resistance to experimental bovine pneumonic pasteurellosis

Using 6- to 8-month-old beef calves, 3 experiments were conducted to compare the effect of vaccination with live or killed Pasteurella haemolytica on resistance to a transthoracic challenge exposure with the organism and to correlate serum antibody response with resistance. In each experiment, calves were vaccinated twice at 1-week intervals and were challenge exposed 21 days after the first inoculation. Lung lesions were evaluated by a system, such that higher scores indicated the more severe lesions. In each experiment, calves immunized with live P haemolytica had lower lesion scores than calves vaccinated with saline solution or bacterin. In 2 of the experiments, the differences were significant (P less than 0.05). In all experiments, calves vaccinated parenterally with a commercial P haemolytica/P multocida bacterin or with a formalin-killed P haemolytica bacterin had lesion scores that were not significantly different (P greater than 0.05) than for control calves vaccinated with saline solution. Live and killed bacterial preparations induced a significant serum antibody response to P haemolytica as measured by a quantitative fluorometric immunoassay. The antibody response to vaccination was not affected by preexisting titers to P haemolytica. Serum antibody titers were not consistently as high for calves vaccinated with bacterins as for calves vaccinated with live organisms. Although high antibody titers correlated with low lesion scores when calves vaccinated with saline solution or live organisms were analyzed collectively, there was not a significant correlation between the 2 variables when calves, vaccinated with saline solution or with bacterin, were analyzed collectively. These data indicate that, although bacterins may induce a detectable serum antibody response, they do not induce protection against transthoracic challenge exposure to P haemolytica.     

Fowl cholera immunity induced by various vaccines in broiler minibreeder chickens determined by enzyme-linked immunosorbent assay

Broiler minibreeder hens were vaccinated for protection against fowl cholera at 12 and 21 weeks of age using several vaccination schemes, which included a live Pasteurella multocida (CU strain) vaccine, two commercial polyvalent fowl cholera oil-based bacterins, and two experimentally prepared polyvalent oil-based bacterins. Some treatment groups received only live or killed vaccines, whereas others received a live vaccine at 12 weeks followed by a killed product at 21 weeks. At 42 weeks of age, all birds that received the live CU vaccine twice or once followed by a bacterin survived challenge. Birds that received killed vaccines only were significantly less protected but still showed a respectable survival rate of 86%. All unvaccinated controls died within 72 hr after challenge. At 72 weeks of age, overall protection was lower than that at 42 weeks, regardless of vaccination treatment. Antibody titers were usually higher in birds that received bacterins than in those receiving live vaccines, yet overall protection was still greater in those birds that received the live cholera vaccine twice.     

Effect of Endobronchial Challenge with Actinobacillus pleuropneumoniae Serotype 10 of Pigs Vaccinated with Bacterins Consisting of A. pleuropneumoniae Serotype 10 Grown under NAD‐Rich and NAD‐Restricted Conditions

The efficacy of two bacterins containing an Actinobacillus pleuropneumoniae serotype 10 strain was evaluated. The bacterial cells constituting bacterin 1 and 2 were grown under nicotinamide adenine dinucleotide (NAD)‐rich (low‐adherence capacity to alveolar epithelial cell cultures) and NAD‐restricted (high‐adherence capacity to alveolar epithelial cell cultures) conditions, respectively. Ten pigs were vaccinated twice with the bacterin 1 and nine pigs with the bacterin 2. Ten control animals were injected twice with a saline solution. Three weeks after the second vaccination, all pigs were endobronchially inoculated with 106.5 colony‐forming units (CFU) of an A. pleuropneumoniae serotype 10 strain. In the bacterin 1 and 2 group, three and two pigs died after inoculation, respectively. Only two pigs of the control group survived challenge. Surviving pigs were killed at 7 days after challenge. The percentage of pigs with severe lung lesions (>10% of the lung affected) was 100% in the control group, 70% in the bacterin 1 group and 22% in the bacterin 2 group. Actinobacillus pleuropneumoniae was isolated from the lungs of all animals. The mean bacterial titres of the caudal lung lobes were 7.0 × 10⁶ CFU/g in the control group, 6.3 × 10⁵ CFU/g in the bacterin 1 group and 1.3 × 10⁶ CFU/g in the bacterin 2 group. It was concluded that both bacterins induced partial protection against severe challenge. Furthermore, there are indications that the bacterin 2, containing A. pleuropneumoniae bacteria grown under conditions resulting in high in vitro adhesin, induced better protection than the bacterin 1.     

Immunity to toxoplasmosis in hamsters

Protective immunity to Toxoplasma was studied in hamsters. Immunity developed in 2 to 3 weeks after vaccinations were performed. Vaccination with live RH, T-45, and ts-4 strains afforded the best protection against challenge exposure with the most pathogenic RH strain used. Even a killed-toxoplasma vaccine protected all hamsters against the slightly less pathogenic T-1 strain through 24 weeks, but it did not protect hamsters against challenge exposure with the RH strain. Both ts-4, a nonpersistent strain, and killed-toxoplasma vaccine provided protective immunity in hamsters that was not dependent upon premunition. Toxoplasma antibody titers in hamsters given the 2 vaccines were similar. However, there was a difference in the quality of immunity: fever and body weight loss were seen in hamsters vaccinated with the killed-toxoplasma vaccine after they were challenge exposed with T-1 strain, whereas these changes were rarely seen in hamsters given the live-toxoplasma vaccine and then challenge exposed with RH strain. Delayed-type hypersensitivity to Toxoplasma antigen always appeared before protective immunity and was detected in all hamsters by 4 days after vaccination with live-toxoplasma strains. Although the development of delayed-type hypersensitivity preceded protective immunity, it was not indicative that protective immunity was present or would develop.     

Immunologic response to Pasteurella haemolytica and resistance against experimental bovine pneumonic pasteurellosis, induced by bacterins in oil adjuvants

Immunogenicity of and protection afforded by Pasteurella haemolytica bacterins were studied in calves. Bacterins contained an aluminum hydroxide in gel (ALH) adjuvant or one of the following oil-in-water adjuvants: Freund's complete adjuvant (FCA), Freund's incomplete adjuvant (FIA), and trehalose dimycolate (TDM). On days 0 and 7, calves were vaccinated with phosphate-buffered saline solution (PBSS), a bacterin, or live P haemolytica. Transthoracic intrapulmonic challenge exposure was done on day 21. In 3 experiments, there were no significant (P greater than 0.05) differences between lung lesions induced in PBSS-or ALH bacterin-vaccinated calves. Both FCA and FIA bacterins significantly (P less than 0.05) enhanced resistance against challenge exposure. Resistance induced by FCA and FIA bacterins was comparable with that induced by vaccination with live P haemolytica. Calves vaccinated with FIA bacterin and challenge-exposed to P haemolytica at a concentration of 4.5 X 10(9) colony-forming units (4.5 times greater than used in the first 3 experiments) resisted challenge exposure similar to calves given live organisms. The TDM bacterin failed to enhance resistance. All bacterins caused a significant increase (P less than 0.05) in serum antibody to P haemolytica somatic antigens, as measured by a quantitative fluorometric immunoassay. Pasteurella haemolytica leukotoxin neutralizing antibody titers did not increase significantly (P greater than 0.05) in sera after vaccination with any bacterin. Vaccination with FCA and FIA bacterins resulted in a significant increase (P less than 0.001) in serum antibody to a carbohydrate-protein subunit of P haemolytica, as measured by an enzyme-linked immunosorbent assay.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Difference in protective immunity of the tongue and feet of guinea pigs vaccinated with foot-and-mouth disease virus type A12 following intradermolingual and footpad challenge

Immunity to Foot-and-Mouth Disease Virus (FMDV) type A12 was developed in guinea pigs by vaccinating them with varying doses of inactivated FMDV inoculated by different routes. Vaccinated animals and FMDV convalescent animals were then tested for differences in protective immunity by challenging each animal with 10³ median guinea pigs infectious doses of FMDV intradermally into the tongue and the heelpad of a rear foot. Protected immunity was evaluated by examining the tongue and feet for the development of vesicles. Protective immunity of the tongue was found to be different from that of the feet. This led to the finding that three levels of protective immunity (LPI) could be distinguished. Convalescent guinea pigs demonstrated the highest level of protective immunity (LPI-1). They did not develop vesicles after a tongue or heelpad challenge. The second level of protective immunity (LPI-2) was shown by animals vaccinated with high doses of FMDV. After a tongue and heelpad challenge, they developed vesicles on the inoculated heelpad, but not on the tongue. The lowest level of protective immunity (LPI-3) was shown by animals vaccinated with lower doses of FMDV. After a tongue and heelpad challenge, they developed vesicles on the tongue and the inoculated foot, but FMDV did not spread to the uninoculated feet. Anti-FMDV antibody titers could not predict the level of protective immunity. Other experimental results show that protective immunity in the heelpad is complex and more difficult to induce than that of the tongue. In addition, the results show the feasibility of using double site challenges of the tongue and a foot for measuring protective immunity in guinea pigs.     

Immunization of pigs against Streptococcus suis serotype 2 infection using a live avirulent strain.

Streptococcus suis capsular type 2 is still an important cause of economic losses in the swine industry. At the present time, vaccination of pigs against this infection is generally carried out with autogenous bacterins and results are equivocal. In this study, the protective effect of a live avirulent S. suis type 2 strain (#1330) which had induced a good protection in mice, was evaluated in swine. The experiment was performed in triplicate using 4 week-old piglets. A total of 15 piglets were vaccinated 3 times, 15 others were vaccinated 2 times, and 15 piglets were injected 3 times with sterile Todd-Hewitt broth. Using an indirect ELISA, an increase in the IgG response to S. suis antigens was noted in 27 of the 30 vaccinated piglets. On day 21 post-vaccination, all animals were challenged intravenously with a virulent S. suis type 2 strain (#999). In the 2 vaccinated groups, 26 animals were fully protected. Only 1 out of the 15 piglets vaccinated 3 times developed mild clinical signs. In the group vaccinated twice, 3 piglets showed clinical signs and 1 of them died after the challenge. In the control group, 7 animals died out of the 11 with clinical signs of infection. In conclusion, a protective immunity was observed in swine when using strain 1330. However, more studies are needed to assess the use of a live S. suis strain in a vaccine for pigs.     

Guinea pig protection test as indicator of potency of oil emulsion foot-and-mouth disease vaccines

A vaccine potency test is described involving virus challenge to six groups of 10 guinea pigs at five weeks after vaccination. Sixteen oil emulsion foot-and-mouth disease vaccines were so tested and nine retested after storage at 4 degrees C for up to 28.3 months. The results were compared with those of the routinely used oil emulsion vaccine potency test (protection afforded to eight pigs challenged 21 days after vaccination). When guinea pig estimates of 3 log2 PD50 or more were obtained, then, with one exception, the batches protected all or almost all pigs from challenge, but when the guinea pig estimates were less than 1 log2 PD50, the vaccines failed to protect five out of eight pigs. The sensitivity and reproducibility of the guinea pig method, established by repeated tests on two vaccine batches, seemed acceptable. The results suggested that guinea pig estimates might provide a suitable substitute for pig challenge potency tests because they reflected the potency of the vaccines, were likely to involve smaller standard errors and caused less discomfort to animals.     

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.     

Strain specificity of the immune response of pigs following vaccination with various strains of porcine reproductive and respiratory syndrome virus

The primary objective of the study was to determine strain specificity of the immune response of pigs following vaccination with selected strains of porcine reproductive and respiratory syndrome virus (PRRSV). The experimental design included five groups (I through V, six pigs per group) free of antibody for PRRSV at the beginning of the experiment (day 0). On day 0, groups III, IV, and V were vaccinated with attenuated versions of PRRSV strains 8, 9, and 14, respectively. On day 21, the immunity of group II (non-vaccinated/challenged controls) and groups III, IV, and V was challenged by exposing each pig to a composite of the virulent versions of these same three strains. On day 35, all pigs, including non-vaccinated/non-challenged pigs of group I, were necropsied. Lungs and selected lymph nodes were examined for lesions. Serum samples obtained at weekly intervals throughout the study and lung lavage fluids obtained at necropsy were tested for the presence of PRRSV and its strain identity. Before challenge the strain of PRRSV identified in the sera of vaccinated pigs was always that with which the particular pig had been vaccinated (i.e. homologous strain), whereas, with one exception, only heterologous strains were identified after challenge. This apparent strain exclusion as a result of vaccination was statistically significant (P = 0.004). The tendency for heterologous strains to predominate after challenge suggests that a pig's immune response to PRRSV has some degree of strain specificity. Whether this finding has any clinical relevance in regard to immunoprophylaxis remains to be determined.     

Evaluation of factors affecting vaccine efficacy of recombinant Marek's disease virus lacking the Meq oncogene in chickens

We previously reported that deletion of the Meq gene from the oncogenic rMd5 virus rendered it apathogenic for chickens. Here we examined multiple factors affecting Marek's disease vaccine efficacy of this nonpathogenic recombinant Meq null rMd5 virus (rMd5deltaMeq). These factors included host genetics (MHC haplotype), strain or dose of challenge virus, vaccine challenge intervals, and maternal antibody status of the vaccinated chicks. Studies on host genetics were carried out in five chicken lines comprising four different MHC B-haplotypes. Results showed that chicken lines tested were highly protected, with protective indexes of 100% (B*2/*15), 94% (B*2/*2), 87% (B*19/*19), and 83% (B*21/*21). At a challenge dose above 8000 plaque-forming units, differences in protection were observed between the two highly virulent strains examined (648A and 686). The interval between vaccination and challenge indicated a protective efficacy from 0 to 2 days varied greatly (12%-82%) after challenge with vv+686, the most virulent virus. Less variation and significant protection began at 3 days post vaccination and reached a maximum at 5 days post vaccination with about 80%-100% protection. Taken together, our results indicate that the factors examined in this study are important for vaccine efficacy and need to be considered in comparative evaluations of vaccines.