De novo identification of bacterial antigens of a clinical isolate by combining use of proteosurfaceomics, secretomics, and BacScan technologies

Background

Emerging infectious diseases pose a significant threat to both human and animal populations. Rapid de novo identification of protective antigens from a clinical isolate and development of an antigen-matched vaccine is a golden strategy to prevent the spread of emerging novel pathogens.

Methods

Here, we focused on Actinobacillus pleuropneumoniae, which poses a serious threat to the pig industry, and developed a general workflow by integrating proteosurfaceomics, secretomics, and BacScan technologies for the rapid de novo identification of bacterial protective proteins from a clinical isolate.

Results

As a proof of concept, we identified 3 novel protective proteins of A. pleuropneumoniae. Using the protective protein HBS1_14 and toxin proteins, we have developed a promising multivalent subunit vaccine against A. pleuropneumoniae.

Discussion

We believe that our strategy can be applied to any bacterial pathogen and has the potential to significantly accelerate the development of antigen-matched vaccines to prevent the spread of an emerging novel bacterial pathogen.

[Construction and characterization of Actinobacillus pleuropneumoniae serovar 7 live attenuated vaccine strain co-expressing ApxIA]

Actinobacillus pleuropneumoniae (A. pleuropneumoniae), the causative agent of porcine contagious pleuropneumonia (PCP), is a significant pathogen of the world pig industry, vaccination is potentially an effective tool for the prevention of PCP. The purpose of present study was to enhance the immunogenicity of A. pleuropneumoniae live vaccine strain HB04C- (serovar 7), which was unable to express ApxIA, and to develop effective multivalent vaccines for the respiratory pathogens based on the attenuated A. pleuropneumoniae. We introduced a shuttle vector containing intact apxIA gene into HB04C-, generating HB04C2, an A. pleuropneumoniae serovar 7 live attenuated vaccine strain co-expressing ApxIA. Then we investigated the biological characteristics of HB04C2. We found that the shuttle vector expressing ApxIA was stable in HB04C2, and the growth ability of HB04C2 was not affected by the shuttle vector. We observed that HB04C2 elicited detectable antibodies against ApxIA and ApxIIA when it was administrated intratracheally as a live vaccine in pigs, and all immunized pigs were protected from heterologous virulent A. pleuropneumoniae (serovar 1) challenge. In conclusion, we demonstrated that A. pleuropneumoniae live vaccine could be used as a vector for expression of heterologous antigens.

Characterization and immunogenicity of an apxIA mutant of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is the aetiological agent of porcine pleuropneumonia, a highly contagious and often fatal disease. A candidate live vaccine strain, potentially capable of cross-serovar protection, was constructed by deleting the section of the apxIA gene coding for the C-terminal segment of ApxI toxin of the A. pleuropneumoniae serovar 10 reference strain (D13039) and inserting a chloramphenicol resistance gene cassette. The mutant strain (termed D13039A(-)Chl(r)) produced an approximately 48kDa protein corresponding to the N-terminus of the ApxI toxin, and exhibited no haemolytic activity and lower virulence in mice compared with the parental strain. The mutant was evaluated in a vaccination-challenge trial in which pigs were given two intra-nasal doses of the mutant at 14 days intervals and then challenged 14 days after the last vaccination with either A. pleuropneumoniae serovar 1 (4074) or serovar 2 (S1536) or serovar 10 (D13039) reference strains. The haemolysin neutralisation titres of the pre-challenge sera were significantly higher in the vaccinated pigs than in the unvaccinated pigs. The mortalities, clinical signs and lung lesion scores in the vaccinated pigs were significantly lower than those in the unvaccinated pigs for the serovar 1 challenge. A significantly lower lung lesion score was also observed in the vaccinated pigs, compared with unvaccinated pigs, for serovar 2 challenge. Our work suggests that the mutant strain offers potential as a live attenuated pleuropneumonia vaccine that can provide cross-serovar protection.

Emulsifier content and side effects of oil-based adjuvant vaccine in swine

Side effects caused by the excessive emulsifier in oil-based adjuvant vaccine were examined practically in swine using one oil-in-water type adjuvant vaccine against swine pleuropneumonia. The vaccine was prepared from cell-free-antigen of Actinobacillus pleuropneumoniae, liquid paraffin, and several polyoxyethylenesorbitan and sorbitan oleates. Based on findings about safety in mice and emulsion stability, 2 vaccines containing either 11.25% or 6.25% emulsifier content were injected intramuscularly twice in swine, as the highest and lowest limits, respectively, within the practical range. All pigs showed temporary fever and malaise with anorexia for several days after each injection. The fever of the higher emulsifier content group took significantly longer to recover than the lower. Malaise also showed a similar tendency. On the other hand, antibody response was sufficiently induced with no significant difference between the 2 groups. Lowering the emulsifier content is a very simple but effective solution for mitigation of side effects without the reduction of adjuvanticity. For safe and high-quality oil-based adjuvant vaccines, not only antigen and base-oil, but emulsifier content must be optimized.

Development of a DIVA subunit vaccine against Actinobacillus pleuropneumoniae infection

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia which leads to high economic losses in the swine industry worldwide. Vaccination against this pathogen is hampered by the occurrence of 15 serotypes, and commonly used whole cell bacterin vaccines are not sufficiently cross-serotype protective. In addition, for generating and maintaining specified pathogen-free herds it is desirable to use DIVA (differentiating infected from vaccinated animals) vaccines. Based on a detergent wash extraction of outer membrane associated proteins and secreted proteins we developed a DIVA vaccine using the immunogenic ApxII toxin which is present in 13 of the 15 A. pleuropneumoniae serotypes as the DIVA antigen. The apxIIA gene was deleted in one strain each of serotypes 1, 2, and 5 using a single-step transconjugation system, and equal parts of detergent washes from these strains served as the vaccine antigen. After intramuscular immunisation all pigs developed a strong humoral immune response to the vaccine antigen and showed no reactivity in an ApxIIA ELISA. Upon challenge all pigs were completely protected from clinical symptoms in trials with a homologous (serotype 2) as well as with a heterologous strain (serotype 9); in addition, colonisation of the challenge strain was clearly reduced but not abolished completely. As a result of the highly efficient protection, however, immunised pigs did not develop antibodies to the DIVA-antigen at levels detectable by ELISA but only by a more sensitive Western blotting approach, thereby demonstrating the challenge in developing appropriate marker vaccines for the livestock industry.

An evaluation of the role of antibodies to Actinobacillus pleuropneumoniae serovar 1 and 15 in the protection provided by sub-unit and live streptomycin-dependent pleuropneumonia vaccines

OBJECTIVE

To evaluate the serological response of pigs receiving either the Porcilis APP vaccine or a modified live vaccine based on a streptomycin-dependent (SD) strain of Actinobacillus pleuropneumoniae, and then challenged with an Australian isolate of A. pleuropneumoniae of either serovar 1 or 15 as a means of understanding the protection provided by both vaccines against serovar 1 but not against serovar 15.

DESIGN

The serological tests evaluated were serovar-specific polysaccharide ELISA tests (for serovar 1 and 15), ELISA tests for antibodies to three A. pleuropneumoniae toxins (ApxI, ApxII and ApxIII) as well as to a 42 kDa outer membrane protein (OMP), a haemolysin neutralisation (HN) assay and immunoblotting. The tests were used to detect antibodies in vaccinated pigs that had been shown to be protected against serovar 1 but not serovar 15.

RESULTS

In the polysaccharide antigen ELISA assays, both vaccines resulted in a significant rise in the titre in the serovar 1 ELISA but not the serovar 15 ELISA. The Porcilis APP vaccinated pigs showed a significant response in the ApxI, ApxIII and 42 kDa OMP ELISA. In the ApxII ELISA, all pigs tested (the Porcilis APP vaccinates and the controls) were positive on entry to the trial. In the HN assay, the Porcilis APP vaccinated pigs showed a significant response after one dose while the SD vaccinated pigs required two doses of vaccine before a marked rise in titre was induced. Immunoblotting revealed that neither vaccine generated antibodies that recognised the ApxIII produced by serovar 15.

CONCLUSIONS

The failure of these vaccines to provide protection against serovar 15 may be due to novel virulence factors possessed by serovar 15, significant differences between the ApxIII toxin of serovar 15 and those present in the Porcilis APP vaccine or failure by both vaccines to induce antibodies to the serovar 15 specific polysaccharide.

Construction and characterization of a live, attenuated apxIICA inactivation mutant ofActinobacillus pleuropneumoniaelacking a drug resistance marker

The apxIIC gene of Actinobacillus pleuropneumoniae serotype 7 was inactivated by homologous recombination using a sucrose counter-selectable marker system, resulting in a mutant strain that had no antibiotic resistance marker and expressed an inactivated ApxII toxin. The safety and immunogenicity of the mutant were evaluated in mice. The mutant strain caused no adverse effects in mice at doses up to 2 x 10(9) CFU via the intraperitoneal route while the parental strain induced total mortality at a dose of 2 x 10(7) CFU. Mice vaccinated intraperitoneally with the mutant strain had 100% and 70% protection against homologous (serotype 7) or heterologous (serotype 1, 3) challenge with A. pleuropneumoniae, respectively. The A. pleuropneumoniae mutant strain HB04C- and the counterselection method used in the study show promise in developing effective live vaccines for porcine pleuropneumonia and for other infections diseases of the respiratory system.

Comparison of the efficacy of a subunit and a live streptomycin-dependent porcine pleuropneumonia vaccine

OBJECTIVE

To evaluate the efficacy of two new-generation porcine pleuropneumonia vaccines when challenged with Australian isolates of Actinobacillus pleuropneumoniae of serovars 1 and 15.

DESIGN

The Porcilis APP vaccine and an experimental streptomycin-dependent strain of A pleuropneumoniae were evaluated in a standardised pen trial. Each vaccine/challenge group consisted of 10 pigs.

RESULTS

With the serovar 1 challenge, the Porcilis APP vaccine and the live vaccine, compared with the control group, gave significant protection in terms of clinical signs, lung lesions, re-isolation scores and average daily gain (ADG) postchallenge. Only the Porcilis APP vaccine provided significant protection against mortality. In the serovar 15 challenged pigs, the only significant difference detected was that the Porcilis APP vaccinated pigs had a better postchallenge ADG than the controls. None of the Porcilis APP vaccinated pigs showed signs of depression postvaccination and none were euthanased after challenge with either serovar 1 or 15. The pigs vaccinated with the live vaccine showed obvious depression after each vaccination and a total of 3 pigs were euthanased after challenge (one with serovar 1 and two with serovar 15).

CONCLUSIONS

Both of the vaccines provided significant protection against a severe challenge with serovar 1 A pleuropneumoniae. Neither vaccine was effective against a serovar 15 A pleuropneumoniae challenge. There was evidence that the Porcilis APP vaccine did provide some protection against the serovar 15 challenge because the ADG, after challenge of pigs given this vaccine, was greater than the control pigs.

Blood lymphocyte subsets in pigs vaccinated and challenged with Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae bacterins do not induce protection in pigs while infection with low doses of the CM5 strain of A. pleuropneumoniae given by aerosol induces complete protection. To evaluate possible correlates of protection in blood lymphocyte subset phenotypes, pigs were treated with a commercial bacterin given intramuscularly, low dose (10(5)cfu/ml) aerosol infection with CM5 or control treatments of the bacterin adjuvant or phosphate buffered saline. All pigs were challenged with a high dose (10(7)cfu/ml) of A. pleuropneumoniae. Lymphocytes and sera were collected prior to and following primary and secondary immunizations and challenge, for evaluation of B- and T-cell markers and antibody to four A. pleuropneumoniae antigens. IgM(micro)+ B-cells were increased following primary exposure to antigen in the bacterin-vaccinated group only. An increase in CD4+ cells in the LD aerosol-infected group was apparent following secondary exposure to antigen. These early changes suggest little difference in lymphocyte populations between treatment groups, however, greater differences were observed following high-dose challenge; CD4+ lymphocytes were increased significantly in both bacterin and LD-challenged groups (p<0.05) while CD8+ cells decreased in the LD-group at this time period. Consequently, there were significant differences (p<0.05) in the CD4:CD8 ratio after high-dose challenge compared to earlier time points and control groups. Variation in cellular expression of SLA-DR and DQ was observed but trends correlating to treatment group were not evident. Complete protection or lack of protection associated with LD challenge or immunisation resulted in significant differences in B-cell frequencies and CD4:CD8 ratio phenotypes in pigs, but only changes in CD4:CD8 ratios appeared relevant to protection.

Attenuation of Actinobacillus pleuropneumoniae by inactivation of aroQ

Actinobacillus pleuropneumoniae is the aetiological agent of porcine pleuropneumonia, a disease resulting in morbidity and mortality of pigs and accordingly economic losses within the swine industry. In order to construct a potential vaccine strain of A. pleuropneumoniae for control of this disease, the aroQ gene, required for the aromatic biosynthetic pathway, was targeted for inactivation. The resulting strain was tested for virulence within pigs. The aroQ gene and an adjacent gene, dapD, were cloned. A recombination cassette, for inactivation of aroQ, was constructed from these cloned genes by inserting an ampicillin resistance gene and this was transformed into A. pleuropneumoniae. Integration of this construct into the chromosomal location of aroQ and disruption of the aroQ/dapD gene arrangement was confirmed through PCR and Southern analysis. The resulting HS25 aroQ mutants were unable to grow in a chemically defined medium and following intratracheal delivery to pigs were only able to induce lung lesions when given at a level 10,000 times greater than that of the parent strain. Complementation with an in trans, functional, aroQ gene restored the ability of the mutant strain to grow in a chemically defined medium and virulence, when tested in pigs, confirming attenuation results from inactivation of aroQ. In conclusion, this work has constructed a defined mutant of A. pleuropneumoniae that is attenuated and may be safely delivered live to pigs.

Actinobacillus pleuropneumoniae surface polysaccharides: their role in diagnosis and immunogenicity

Actinobacillus pleuropneumoniae is an important pig pathogen that is responsible for swine pleuropneumonia, a highly contagious respiratory infection. Knowledge of the importance, composition and structural determination of the major antigens involved in virulence provides crucial information that could lead to the development of a rationale for the production of specific serodiagnostic tools as well as vaccine development. Thus, efforts have been devoted to study mainly A. pleuropneumoniae virulence determinants with special emphasis on the Apx toxins (for A. pleuropneumoniae RTX toxins). In comparison, little attention has been given to the surface polysaccharides, which include capsular polysaccharides (CPS) and cell-wall lipopolysaccharides (LPS). Here, we review current knowledge on CPS and LPS of A. pleuropneumoniae used as diagnostic tools to monitor the infection and as immunogens for inclusion in vaccine preparations for animal protection.

Effectiveness of doxycycline in the prevention of an experimental infection with Actinobacillus pleuropneumoniae in pigs

The effectiveness of medication with doxycycline in feed in the control of pleuropneumonia in pigs was tested using an Actinobacillus pleuropneumoniae serotype 1 aerosol challenge model. Two groups of 10 animals were used for the challenge, a 'medicated group' and an 'unmedicated group'. A third group of four animals was used as a 'control group'. Pigs from the medicated group were provided with feed containing 250 p.p.m. doxycycline (HIPRAMIX/DOXI) for 8 consecutive days and were challenged on the fifth day of treatment. No clinical signs were observed in pigs from the 'control group'. Four animals from the 'unmedicated group' died within the first 48 h after challenge with clinical and lesional evidence of an acute form of pleuropneumonia. Clinical signs of animals surviving the first 48 h were progressively less severe and showed lesions similar to those described for subacute-chronic forms of the disease. However, only one animal from the 'medicated group' showed clinical signs of a chronic form of pleuropneumonia. Reisolation of A. pleuropneumoniae was more evident from lung tissues of animals fed the doxycycline-free feed (70%), coinciding with the presence of both acute and subacute lesions. However, the micro-organism could be reisolated from only one animal which belonged to the 'medicated group'. It is concluded that the treatment of pigs with 250 p.p.m. doxycycline (HIPRAMIX/DOXI) prevents disease caused by A. pleuropneumoniae.

Prevention of pleuropneumonia in pigs by in-feed medication with sulphadimethoxine and sulphamethoxazole in combination with trimethoprim

The prophylactic effect of in-feed medication of conventional pigs with sulphadimethoxine (SDM), sulphamethoxazole (SMX), and trimethoprim (TMP) was tested by using an Actinobacillus pleuropneumoniae infection model. In each of five experiments, six pigs were given medicated feed twice daily and three pigs received antibiotic-free feed and served as positive (unmedicated, infected) controls. The following drugs or drug combinations were tested (in mg per kg feed): 500 SDM + 100 TMP, 500 SMX + 100 TMP, 125 SMX + 25 TMP, 125 SMX (alone) and 25 TMP (alone). After six days of feed medication, all animals were endobronchially inoculated with A. pleuropneumoniae in a dose of 1-3.10(4) colony-forming units (CFU). The response to the challenge in all control pigs was characterized by fever, lethargy, anorexia, reduced water consumption, and laboured breathing. At autopsy all controls manifested a fibrinous haemorrhagic pleuropneumonia. In-feed medication with 500 SDM + 100 TMP, 500 SMX + 100 TMP as well as 125 SMX + 25 TMP resulted in an effective protection against the challenge in all treated animals. After consumption of feed medicated with 125 mg per kg SMX or 25 mg per kg TMP, pleuropneumonia was evident in all challenged pigs. The results of this study indicate an in vivo potentiation of SMX and TMP in pigs against this respiratory tract pathogen.

Towards an understanding of equine pleuropneumonia: factors relevant for control

OBJECTIVE

To review relevant literature on factors associated with the development of equine pleuropneumonia.

DESIGN

A review of the literature using a range of databases including Current Contents, Medline, ChemAbstracts, Biological Abstracts and CAB and a comprehensive search strategy which involved use of keywords, author and subject category searches. Additional sources included review of articles cited by key accumulated references.

RESULTS

Since the early years of this century, many of the "gaps" in our knowledge of the pathogenesis of this disease have been filled. We now know that equine pleuropneumonia results from contamination of the lower respiratory tract with bacteria similar to the normal oropharyngeal microbiota of the horse and that transportation of any mode, especially over long distances (and consequently with no or short rest periods), is the single most important predisposing factor for this disease. This is associated with restraint of horses such that they are unable to lower their heads, which leads to increased opportunity for lower respiratory tract contamination and a reduced opportunity for clearance. Strenuous exercise also results in lower respiratory tract contamination and exercise subsequent to transportation exerts additive detrimental effects on the defenses of the lower respiratory tract.

CLINICAL IMPLICATIONS

While modern veterinary medicine and surgery have significantly reduced the death rate from pleuropneumonia, horses that develop the disease have a high probability of not returning to their prior use. This underscores the importance of developing the most effective strategies for its prevention.

Efficacy of florphenicol premix in weanling pigs experimentally infected with Actinobacillus pleuropneumoniae

The efficacy of a florfenicol premix was studied in weaning pigs experimentally inoculated with Actinobacillus pleuropneumoniae. Twenty five clinically healthy pigs were distributed into 3 groups; group A non-medicated, groups B and C orally medicated with 20 and 40 ppm of florfenicol respectively. The pigs were fed during 12 consecutive days and on day 5 all the groups were challenged with A. pleuropneumoniae serotype 1. All the animals in Group A developed clinical signs. Most of the pigs in the medicated groups maintained a good health status. Postmortem examination revealed severe pleuropneumonia in pigs from the control group and pneumonic lesions in 40% of the animals treated with 20 ppm of florfenicol. Development of pleuropneumonia was prevented in all the pigs medicated with 40 ppm of florfenicol. Actinobacillus pleuropneumoniae was recovered from the lungs of all control animals and from one pig of each of the medicated groups, however, the avidin biotin peroxidase (ABC-P) method detected the presence of the microorganism in all the animals. We demonstrated that medication with feed containing 40 ppm of florfenicol blocked efficiently the signs and lesions caused by A. pleuropneumoniae and increased the daily body weight gain.

Vaccination and protection of pigs against pleuropneumonia with a vaccine strain of Actinobacillus pleuropneumoniae produced by site-specific mutagenesis of the ApxII operon

The production of toxin (Apx)-neutralizing antibodies during infection plays a major role in the induction of protective immunity to Actinobacillus pleuropneumoniae reinfection. In the present study, the gene encoding the ApxII-activating protein, apxIIC, was insertionally inactivated on the chromosome of a serovar 7 strain, HS93. Expression of the structural toxin, ApxIIA, and of the two genes required for its secretion, apxIB and apxID, still occurs in this strain. The resulting mutant strain, HS93C- Ampr, was found to secrete the unactivated toxin. Pigs vaccinated with live HS93C- Ampr via the intranasal route were protected against a cross-serovar challenge with a virulent serovar 1 strain of A. pleuropneumoniae. This is the first reported vaccine strain of A. pleuropneumoniae which can be delivered live to pigs and offers cross-serovar protection against porcine pleuropneumonia.

Protective efficacy of an affinity-purified hemolysin vaccine against experimental swine pleuropneumonia

Protective efficacy of Actinobacillus pleuropneumoniae extracellular hemolytic toxins, RTX-toxin I (Apx I) and Apx II, was evaluated in pigs. The hemolysins were purified from culture supernatant of A. pleuropneumoniae strain HA-337, serotype 1 by immunoaffinity chromatography using a monoclonal antibody specific for Apx I or Apx II as ligand. Four pigs were vaccinated with the purified hemolysins absorbed on aluminum phosphate gel adjuvant. Four pigs of a control group were given placebo. Hemolysin-neutralizing antibodies were detected only in vaccinated group after booster injection. One of four control pigs died following an aerosol challenge with the homologous strain, and three surviving pigs developed serious clinical signs of pneumonia and had extensive lung lesions. In contrast, there was no mortality in vaccinated group. Only transient hyperthermia was observed in two vaccinated pigs after challenge. A necropsy, two vaccinated pigs had slight localized pulmonary lesions, though the remaining two had no lung lesions at all. These results indicate that the hemolysin vaccine made of Apx I and Apx II has good protective activity against swine pleuropneumonia caused by A. pleuropneumoniae serotype.

Aerosol exposure of pigs to viable or inactivated Actinobacillus pleuropneumoniae serotype 9 induces antibodies in bronchoalveolar lining fluids and serum, and protects against homologous challenge

A dose-defined nose-only inhalation system for pigs was used to study the immunogenic and protective potentials of a single aerosol application of viable or killed Actinobacillus pleuropneumoniae serotype 9. Respiratory volumes were measured for each pig to calculate inhaled individual doses. Eight pigs inhaled 107 CFU A. pleuropneumoniae CVI 13261 reference strain for serotype 9. Another eight pigs received an identical dose of killed actinobacilli. After three weeks the pigs and nonexposed controls were challenged with 108 CFU of the homologous strain by aerosol. Bronchoalveolar lavage (BALF) in pigs was performed during the experiment to obtain lavage samples for assessment of local antibodies. Isotype-specific antibody responses in serum and BAL fluids were measured by ELISAs based on whole-cell antigens. The protective efficacy of aerosol immunization was evaluated by clinical and post-mortem examinations. The controls developed fever and severe pleuropneumonia, whereas previously exposed pigs had less fever and less extensive gross pulmonary lesions. After the first aerosol exposure pulmonary IgM, and IgG antibodies reactive with A. pleuropneumoniae increased significantly in both aerosol exposed groups. IgA in BALF and serum concentrations of each Ig class were significantly increased in the group exposed to viable bacteria when compared to the non-exposed controls. After aerosol challenge a pronounced increase of systemic and pulmonary IgA, IgM, and IgG antibodies was detected in both exposure groups. Aerosol application of whole-cell A. pleuropneumoniae bacterins induced similar protective effects against aerosol challenge infection as administration of an identical dose of viable bacteria. Inhalation of A. pleuropneumoniae may lead to asymptomatic carriers in some pigs that could spread the disease under field conditions.

Evaluation of pig lungs following an experimental challenge with Actinobacillus pleuropneumoniae serotype 1 and 5 in pigs inoculated with either hemolysin protein and/or outer membrane proteins

Histopathological changes were compared in pigs challenged with Actinobacillus pleuropneumoniae serotype 1 and serotype 5 after inoculation with subunit vaccines. The vaccines consisted of outer membrane protein and/or hemolysin protein isolated from Actinobacillus pleuropneumoniae serotype 1 or both subunits combined. Twenty-seven cross-bred pigs were separated into six groups: Groups I and IV were vaccinated and boostered with 1500 micrograms outer membrane protein; Groups II and V were vaccinated and boostered with 250 micrograms hemolysin protein; Groups III and VI were vaccinated and boostered with a combination of 1500 micrograms outer membrane protein and 250 micrograms hemolysin protein. Groups I, II and III were challenged with A. pleuropneumoniae serotype 1; and Groups IV, V and VI were challenged with A. pleuropneumoniae serotype 5. Groups III and VI demonstrated the least severe lung tissue damage, with significantly lower (P < 0.05) lung involvement as compared to the other groups. Lesions were noted in all six groups. These results showed that complete protection against A. pleuropneumoniae infection was not feasible using a subunit vaccine consisting of just outer membrane protein and hemolysin protein, and that some cross-protection did occur.

Efficacy of an Actinobacillus pleuropneumoniae bacterin against serotypes 1, 3, 5 and 9

A trial was performed in a swine research facility to ascertain the protection provided by a polyvalent Actinobacillus pleuropneumoniae (APP) bacterin containing serotypes 1, 3, 5 and 9. The test animals consisted of 60, eight-week-old, piglets, which were randomly divided into four main groups. The four main groups were further divided into three sub-groups (I, II, III) of five pigs each. Subgroup I was vaccinated intramuscularly, sub-group II was vaccinated subcutaneously, and sub-group III served as the unvaccinated control group. Each main group was challenged with a single APP serotype (1, 3, 5 or 9). Criteria for evaluation of the bacterin efficacy were mortality, lung lesions, pleural adhesions, and isolation of APP from tonsil or lung. Significant effects of vaccination over nonvaccination were reduced mortality, lung lesions, pleural adhesions, and isolations of APP from tonsil and lung. There were no significant differences between the intramuscular and subcutaneous routes of vaccination. It was concluded that the four-way APP bacterin used in this study provided satisfactory protection against homologous challenge. Evidence of protection was lower mortality and lung lesions and increased daily weight gains in vaccinates as compared with controls.

Prophylaxis of pleuropneumonia in pigs by in-feed medication with oxytetracycline and the subsequent transmission of infection

The prophylactic effect of in-feed medication with oxytetracycline was tested by using an Actinobacillus pleuropneumoniae aerosol challenge model. Groups of 10 conventional pigs were provided with feed containing 400, 800, 1200 or 1600 mg oxytetracycline/kg and fed ad libitum. After six days of medication the pigs were challenged and clinical signs were recorded. Two groups of four unmedicated pigs served as controls and were euthanased 36 to 48 hours after challenge and dissected. The feed medication was continued for nine days after the challenge, and the different treatment groups were then moved to separate accommodation where they were mixed with seronegative tracer pigs. The steady state concentrations of oxytetracycline in the pigs' serum after six days medication with feed containing 400, 800, 1200 or 1600 mg oxytetracycline/kg ranged from 0.07 to 0.13, 0.21 to 0.46, 0.27 to 0.46 and 0.35 to 0.56 microgram/ml, respectively. One of the eight unmedicated control pigs died, and the other seven showed signs of pleuropneumonia post mortem. Medication with feed containing 400 mg and 800 mg oxytetracycline/kg failed to prevent pleuropneumonia in the challenged pigs, and the mortality rates in these groups were two out of 10 and one out of nine pigs, respectively. All the pigs given feed containing 1200 and 1600 mg oxytetracycline/kg survived and only two of the pigs in the first treatment group showed mild clinical signs. No clinical signs were observed in the tracer pigs which were mixed with the pigs medicated with 400, 800 or 1200 mg oxytetracycline/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective immunity following immunisation of pigs with aerosol of Actinobacillus pleuropneumoniae serotype 2

To introduce antigen to the respiratory mucosa, killed Actinobacillus pleuropneumoniae with quil A as adjuvant was administered to pigs as an aerosol. Immunisation by this aerosol induced a marked IgA response in the bronchoalveolar and nasal fluids, and in the serum. Following challenge with live bacteria two weeks after the last exposure to the aerosol, the immunised pigs were protected from the severe pleuropneumonia which developed in non-immunised pigs. The immunised pigs had lower antibody titres in the mucosal fluids and serum after exposure to the challenge. The immune response after experimental infection of non-immunised animals was a weak IgA antibody response in the bronchoalveolar and nasal fluids, whereas the systemic immune response after challenge included both IgA and IgG antibodies.

Testing of remedial measures in fattening pig herds affected with subclinical infections of Actinobacillus pleuropneumoniae serotype 2

The present investigation comprised 5 specialized herds of slaughter pigs, each with a production of 1,500 to 4,000 fatteners per year. High prevalence of pleuritis was demonstrated in all herds at slaughter. Serological investigations by means of ELISA were carried out to determine antibody titres to Actinobacillus pleuropneumoniae (A. pl.) serotype 2 during the fattening period and at slaughter. The investigations showed that this agent was a predominant cause of the subclinical pleuritis although A. pl. was difficult to isolate. An environment study was performed in all herds and major environmental deficiencies were corrected during the course of the investigation. Similarly, all herds changed to a strict routine of batch rearing. In 4 herds out of 5, the animals were vaccinated on arrival to the growing-finishing units and again generally 3-4 weeks later with an inactivated vaccine against A. pl. serotype 2. The prevalence of pleuritis decreased with 25-75% during the three-year observation period. Also the prevalence of pneumonia decreased at the same time. Conversely, daily weight gain and feed conversion improved. The prevalence of pleuritis and pneumonia registered at slaughter was lower in three-breed crosses (including Hampshire, Landrace and Yorkshire) than in the two-breed crosses with Landrace and Yorkshire.

Prophylactic application of Propionibacterium avidum KP-40 in swine with acute experimental infections. II. Bacterial infections: pleuropneumonia and swine erysipelas

The potent immunomodifier Propionibacterium avidum KP-40 (PA) demonstrated prophylactic potency in swine infected experimentally with Haemophilus (Actinobacillus) pleuropneumoniae or Erysipelothrix rhusiopathiae. Animals received PA either together with the respective vaccine or PA only; 3 resp. 4 weeks later all animals were inoculated with virulent pathogens. Eight of 10 swine immunized with inactivated pleuropneumonia vaccine developed mild-moderate forms of infection with temporary stagnation of body weight; application of the vaccine together with PA lowered the morbidity rate to 1 of 10 (p < 0.05). Also in non-vaccinated swine infected with pleuropneumonia or erysipelas PA application resulted in milder clinical symptoms, faster recovery and a larger gain of body weight.

Protective efficacy of conjugate vaccines against experimental challenge with porcine Actinobacillus pleuropneumoniae

In an attempt to protect pigs against swine pleuropneumonia induced by Actinobacillus pleuropneumoniae (SPAP) by neutralizing the effects of three virulence factors of A. pleuropneumoniae--the capsular polysaccharide (CP), the lipopolysaccharide (LPS), and the hemolysin protein (HP)--two subunit conjugate vaccines were prepared by covalently coupling the CP to the HP and the LPS to the HP. The CP, LPS, and HP were isolated from A. pleuropneumoniae, strain 4074, serotype 1, and the protective efficacy of the conjugate vaccines in swine experimentally infected with A. pleuropneumoniae was evaluated. Following a booster vaccination, a significant (P < 0.05) IgG antibody response to the CP, LPS, and HP was detected in the vaccinated pigs. The pigs vaccinated with the CP-HP and LPS-HP conjugates exhibited significantly less mortality (P < 0.05) and significantly greater weight gain (P < 0.001) than unvaccinated pigs. Vaccinated pigs exhibited significantly fewer and less extensive gross pulmonary lesions (P < 0.001) when compared with unvaccinated pigs. Thus, on the basis of mortality, weight gains, and pulmonary lesion formation, the two conjugate vaccines used in conjunction with one another provide noticeable protective efficacy against SPAP.

Pneumocystis carinii pleuropneumonia after aerosolized pentamidine prophylaxis

We observed an atypical Pneumocystis infection with spontaneous pneumothorax, bronchopleural fistulae, an apical cyst and Pneumocystis pleuritis after aerosolized pentamidine prophylaxis in an AIDS patient. These findings suggest a failure of pentamidine aerosol in controlling active Pneumocystis infection in peripheral pulmonary areas. A relapse of Pneumocystis carinii pneumonia (PCP) must be suspected when pneumothorax occurs during secondary prophylaxis with aerosolized pentamidine. It should always be confirmed by bronchoalveolar lavage or transbronchial or open biopsy. Cases presenting as atypical Pneumocystis pneumonia may additionally reveal extrapulmonary dissemination of Pneumocystis infection.

Improved protection of swine from pleuropneumonia by vaccination with proteinase K-treated outer membrane of Actinobacillus (Haemophilus) pleuropneumoniae

The immunogenic and protective potentials of an outer membrane-enriched fraction (OM) from a serotype 5 strain of Actinobacillus (Haemophilus) pleuropneumoniae (APP) and the same OM degraded with proteinase K or periodate were evaluated in swine. Groups of pigs were vaccinated with two doses of OM, proteinase K-treated OM (P-OM), periodate-treated OM (PI-OM), or placebo vaccine and challenged intranasally with the homologous strain of APP. Results from triplicate experiments indicated that proteinase K treatment of OM resulted in an improved efficacy. This improved efficacy of P-OM vaccine over untreated OM vaccine was evidenced not only by less severe lung lesions in P-OM vaccinated pigs but also by significant reduction (P less than 0.05) in the number of P-OM vaccinated pigs which developed lung lesions upon challenge with APP. Assessment of sera from vaccinated animals by immunoblotting, complement fixation test, or ELISA indicated that the immunogenicity of some but not all protein or carbohydrate components were reduced (or eliminated) by proteinase K and periodate treatments respectively.

Passive protection of piglets by monoclonal antibodies against experimental infection with Actinobacillus pleuropneumoniae

Mouse monoclonal antibodies 11C11 (an IgG) and 4A9 (an IgM), which combine with a superficial component of cells belonging, respectively, to serovars 1 or 3 of Actinobacillus pleuropneumoniae, were given intraperitoneally 24 hours before and intranasally one hour before two-week-old, colostrum-deprived piglets were exposed by the intranasal route to 10(9) viable cells of either strain Shope 4074 (serovar 1) or 2/10 (serovar 3). Compared with control piglets given phosphate buffered saline or the heterologous monoclonal antibody, this procedure conferred substantial protection against the development of peracute or acute pleuropneumonia. Protection against the experimental disease was somewhat less in other piglets to which monoclonal antibody 4A9 was given only by the intranasal route one hour before the organism was administered than in those given the antibody intraperitoneally 24 hours beforehand, although its effect was still significantly greater than in piglets given phosphate buffered saline only. These two monoclonal antibodies consequently offer means of investigating at the molecular level the pathogenesis of the disease associated with A pleuropneumoniae and the potential value of anti-idiotypes as immunising agents.

Comparison of conventional and long-acting oxytetracyclines in prevention of induced Actinobacillus (Haemophilus) pleuropneumoniae infection of growing swine

These experiments tested the hypothesis that long-acting oxytetracycline (oxytetracycline-LA) was more effective than regular oxytetracycline in preventing porcine pleuropneumonia when administered either 24 or 48 h prior to experimental challenge with virulent strains of Actinobacillus pleuropneumoniae. Two experiments (1 and 2) were conducted using growing pigs (average weight 12-15 kg). Antibiotic treatments were administered once intramuscularly at 20 mg/kg body weight; controls received an equivalent volume of saline. Clinical signs were recorded over seven days, and mortality rates and pathological lesions were analyzed using analysis of variance. Serum oxytetracycline levels were compared 48 and 72 h postinjection. All pigs developed clinical disease following experimental infection. Actinobacillus pleuropneumoniae was recovered from 42% of experiment 1 pigs and all of experiment 2 pigs. The data showed that both oxytetracycline and oxytetracycline-LA given at the same dose protected pigs against experimental infection when given 24 h prior to challenge, and there was no difference between the efficacy of the two drugs in this experiment. When administered 48 h prior to challenge, only oxytetracycline-LA reduced the clinical signs and pathological changes following A. pleuropneumoniae challenge. Between 48 and 72 h postinjection, oxytetracycline-LA blood levels were significantly greater compared to oxytetracycline-treated pigs.

Actinobacillus (Haemophilus) pleuropneumoniae infections in swine: serological investigations and vaccination trials in combination with environmental improvements

The present investigation comprised six integrated herds (100-150 sows each) and one specialized fattening herd. Serologic tests by ELISA were performed on blood samples from piglets and growing pigs during various rearing phases in order to determine the presence of Actinobacillus infection and to estimate the age of the animals at onset of the disease. Using this information, herd-specific vaccination programs were designed against Actinobacillus pleuropneumoniae serotype 2. The weaned piglets in the integrated herds were vaccinated twice before being moved to the fattening unit. In the specialized fattening herd, the pigs were vaccinated on arrival at the growing unit and just before transfer to the finishing unit. The frequencies of chronic pleuritis at slaughter demonstrated that a vaccination program adapted to the herd-specific problem, in combination with environmental improvements, reduces the prevalence of chronic pleuritis. On the other hand, only a moderate reduction of the prevalence of chronic pleuritis occurred as a result of vaccination if no environmental improvements were made. In two of the herds during the vaccination period, the number of feeding days and food consumption decreased, while growth per day increased. There was also an apparent correlation between higher serum titres and a decreased prevalence of pleuritis at slaughter in three of the herds.

[Experiences with vaccination against Haemophilus pleuropneumonia of swine]

In a Haemophilus pleuropneumonia problem herd with piglet production and fattening, sows and weaned pigs were vaccinated with a Danish vaccine (Pleurinord). Due to consequent vaccination of the sows the health of the piglets could be improved decisively, resulting in an increased number of raised piglets per sow and year from 16.8 to 20.3. In the vaccinated fattening pigs compared to the unvaccinated ones the following effects were observed: markedly reduced expenses for medication and a markedly reduced frequency of characteristic lesions in the respiratory tract; the improvement of the daily weight gains and the reduction of losses remained behind the expectations. Decisive causes for this were respiratory and enteric diseases unrelated to Haemophilus, which were favoured by serious mismanagement and inadequacies in the feeding regimen and barn climate. On the example of the vaccinated herd it is shown how important the analysis of a multifactorial disease situation is, in order to be able to objectify better or at all the influence of a vaccination program under field conditions. Within a concept of prevention and control of Haemophilus pleuropneumonia the vaccination is a helpful part.

Protective efficacy of capsule extracts of Haemophilus pleuropneumoniae in pigs and mice

Capsular extracts of Haemophilus pleuropneumoniae, Serotype 1, were mixed with AL(OH)3 gel (3 parts extract + 1 part Al(OH)3) and used as vaccines in pigs and mice. Four preparations were tested in Experiment I: NaCl and Cetavlon (hexadecyltrimethyl ammonium bromide) extracts of both low in vitro passage (LP) and high in vitro passage (HP) culture, respectively. Four pigs vaccinated with the NaCl extract of the LP strain survived, whereas one of four from each of the remaining vaccine groups and five of six from the control group died. All vaccines induced complement-fixing antibodies. No apparent boosting of titres occurred as a result of challenge with live bacteria. Mice were vaccinated in Experiment II with NaCl and Cetavlon extracts of the LP strain. Both were protective, although the Cetavlon vaccine appeared more efficacious than the NaCl extract. The use of Al(OH)3 adjuvant improved the efficacy of the NaCl vaccine in mice. In Experiment III six gnotobiotic pigs were vaccinated with a combined NaCl and Cetavlon vaccine and seven animals were given placebo. In Experiment IV seven specific pathogen-free (SPF) pigs were given the combined vaccine and eight pigs received placebo treatment. Both of these experiments indicated that the extract vaccines did not completely protect but reduced the mortality in pigs challenged with homologous virulent H. pleuropneumoniae bacteria. The results indicate that capsular antigens of H. pleuropneumoniae have some protective immunogenic efficacy in pigs and mice.

Haemophilus pleuropneumoniae (Actinobacillus pleuropneumoniae). Serotypes 8, 3 and 6. Serological response and cross immunity in pigs

Immunity obtained by vaccination with Haemophilus pleuropneumoniae is type specific and protection will only be obtained against the serotype contained in the vaccine. Serotype 8 is closely related to serotypes 3 and 6 and the objective of the present study was therefore to examine if cross immunity between the three serotypes could be obtained at vaccination.

Vaccination against pleuropneumonia of pigs caused by Haemophilus pleuropneumoniae

A strain of Haemophilus pleuropneumoniae was isolated from a pig with pleuropneumonia from a herd where this condition was frequent. A formalin inactivated culture of this isolate was used as antigen in two vaccine preparations: A and B. Vaccine A had peanut oil + arlacel 80 + tween 80 as adjuvant and vaccine B had aluminum hydroxide gel as adjuvant. Twenty pigs were vaccinated twice with vaccine A and 19 with vaccine B. Twenty additional pigs were not vaccinated. All pigs were transferred to the herd. Eleven pigs in the nonvaccinated group developed pneumonia and seven of these died within eight days after exposure. None of the vaccinated pigs had signs of pneumonia. It is concluded that the vaccines prevented the acute form of pleuropneumonia due to H. pleuropneumoniae.

Pleuropneumonia of swine caused by Haemophilus parahaemolyticus. Studies on the protection obtained by vaccination

Sixty-six pigs were vaccinated with formaldehyde-killed 24-hour or 6-hour culture of H. parahaemolyticus with Freund's incomplete adjuvant (1:1 or 3:1) or 15 per cent Alhydrogel. The vaccine was injected subcutaneously when the pigs were 9 weeks old. A booster injection was given 2 weeks later. Two weeks after the booster injection the pigs were challenged by intranasal inoculation of 10(10) organisms. The efficacy of the vaccine was evaluated by clinical observations and autopsy findings. Vaccines with Alhydrogel adjuvant: With 24-hour culture 25 per cent of the pigs were protected. With 6-hour culture the protection reached 67 per cent. Vaccines with Freund's incomplete adjuvant: With 24-hour culture 67 per cent of the vaccinates were protected. With 6-hour culture 90 per cent were protected. It is concluded that a 6-hour culture of H. parahaemolyticus is superior to an older culture in immunizing power. Vaccine with Freund's incomplete adjuvant caused severe local reaction with persistent granuloma formation. For that reason it is questionable whether this vaccine will be accepted for field use. H. parahaemolyticus could be found in the respiratory tract, also of animals that were protected by vaccination. Further studies on the significance and duration of the carrier state in this infection are required.