Cytological and immunological changes in bronchoalveolar lavage fluid and histological observation of lung lesions in pigs immunized with Mycoplasma hyopneumoniae inactivated vaccine prepared from broth culture supernate

Characterization of a Mycoplasma hyopneumoniae aerosol infection model in pigs

The purpose of the present study was to develop and characterize an experimental aerosol model for Mycoplasma hyopneumoniae (M. hyopneumoniae) infection and respiratory disease in pigs. The experiment was carried out to determine the pathogenicity, colonization, mucosal immune response, and clinical course of disease of dose-controlled aerosols of M. hyopneumoniae. Four groups of three M. hyopneumoniae-free gilts each were individually exposed to aerosols of diluted lung homogenate containing M. hyopneumoniae strain 232 in a chamber. Each group was exposed to different doses of viable organisms (105 to 106 color changing units/mL during 15-20 or 30-35 min in two consecutive days). Nasal, laryngeal, and deep-tracheal secretions were collected from each gilt at 0, 7, 14, 21, and 28 days post-exposure (dpe). Blood samples were collected at 0 and 28 dpe. At necropsy, lung lesions were assessed, and bronchial secretions and bronchoalveolar lavage fluid (BALF) were collected from each lung set. Blood was used to assess seroconversion by means of an indirect ELISA, while BALF, deep-tracheal and nasal secretions were tested by modifying the ELISA to evaluate mucosal IgG and IgA production. Nasal, laryngeal, deep-tracheal, and bronchial secretions were tested by real-time PCR to evaluate bacterial load. Gilts became infected irrespective of the infectious dose, as determined by M. hyopneumoniae detection in deep-tracheal secretions from all gilts at 7 dpe. A specific local humoral immune response starting at 14 dpe was detected in all gilts. While all experimental groups presented gilts with some extent of mycoplasmal pneumonia, only the exposure of gilts to high-dose aerosols consistently reproduced typical clinical signs and severe lung lesions. These results showed that the reproduction of mycoplasmal pneumonia by means of infectious aerosols can be successfully achieved at experimental level, making this model a valuable alternative to evaluate preventive and treatment measures against M. hyopneumoniae.

Improving Mycoplasma hyopneumoniae diagnostic capabilities by harnessing the infection dynamics

Mycoplasma hyopneumoniae remains one of the most problematic bacterial pathogens for pig production. Despite an abundance of observational and laboratory testing capabilities for this organism, diagnostic interpretation of test results can be challenging and ambiguous. This is partly explained by the chronic nature of M. hyopneumoniae infection and its tropism for lower respiratory tract epithelium, which affects diagnostic sensitivities associated with sampling location and stage of infection. A thorough knowledge of the available tools for routine M. hyopneumoniae diagnostic testing, together with a detailed understanding of infection dynamics, are essential for optimizing sampling strategies and providing confidence in the diagnostic process. This study reviewed known information on sampling and diagnostic tools for M. hyopneumoniae and summarized literature reports of the dynamics of key infection outcomes, including clinical signs, lung lesions, pathogen detection, and humoral immune responses. Such knowledge could facilitate better understanding of the performance of different diagnostic approaches at various stages of infection.

Perspectives for improvement of Mycoplasma hyopneumoniae vaccines in pigs

Mycoplasma hyopneumoniae (M. hyopneumoniae) is one of the primary agents involved in the porcine respiratory disease complex, economically one of the most important diseases in pigs worldwide. The pathogen adheres to the ciliated epithelium of the trachea, bronchi, and bronchioles, causes damage to the mucosal clearance system, modulates the immune system and renders the animal more susceptible to other respiratory infections. The pathogenesis is very complex and not yet fully understood. Cell-mediated and likely also mucosal humoral responses are considered important for protection, although infected animals are not able to rapidly clear the pathogen from the respiratory tract. Vaccination is frequently practiced worldwide to control M. hyopneumoniae infections and the associated performance losses, animal welfare issues, and treatment costs. Commercial vaccines are mostly bacterins that are administered intramuscularly. However, the commercial vaccines provide only partial protection, they do not prevent infection and have a limited effect on transmission. Therefore, there is a need for novel vaccines that confer a better protection. The present paper gives a short overview of the pathogenesis and immune responses following M. hyopneumoniae infection, outlines the major limitations of the commercial vaccines and reviews the different experimental M. hyopneumoniae vaccines that have been developed and tested in mice and pigs. Most experimental subunit, DNA and vector vaccines are based on the P97 adhesin or other factors that are important for pathogen survival and pathogenesis. Other studies focused on bacterins combined with novel adjuvants. Very few efforts have been directed towards the development of attenuated vaccines, although such vaccines may have great potential. As cell-mediated and likely also humoral mucosal responses are important for protection, new vaccines should aim to target these arms of the immune response. The selection of proper antigens, administration route and type of adjuvant and carrier molecule is essential for success. Also practical aspects, such as cost of the vaccine, ease of production, transport and administration, and possible combination with vaccines against other porcine pathogens, are important. Possible avenues for further research to develop better vaccines and to achieve a more sustainable control of M. hyopneumoniae infections are discussed.

Genomic Variability and Post-translational Protein Processing Enhance the Immune Evasion of Mycoplasma hyopneumoniae and Its Interaction With the Porcine Immune System

Mycoplasma hyopneumoniae (M. hyopneumoniae, Mhp) is a geographically widespread and economically devastating pathogen that colonizes ciliated epithelium; the infection of Mhp can damnify the mucociliary functions as well as leading to Mycoplasma pneumonia of swine (MPS). MPS is a chronic respiratory infectious disease with high infectivity, and the mortality can be increased by secondary infections as the host immunity gets down-regulated during Mhp infection. The host immune responses are regarded as the main driving force for the disease development, while MPS is prone to attack repeatedly in farms even with vaccination or other treatments. As one of the smallest microorganisms with limited genome scale and metabolic pathways, Mhp can use several mechanisms to achieve immune evasion effect and derive enough nutrients from its host, indicating that there is a strong interaction between Mhp and porcine organism. In this review, we summarized the immune evasion mechanisms from genomic variability and post-translational protein processing. Besides, Mhp can induce the immune cells apoptosis by reactive oxygen species production, excessive nitric oxide (NO) release and caspase activation, and stimulate the release of cytokines to regulate inflammation. This article seeks to provide some new points to reveal the complicated interaction between the pathogen and host immune system with Mhp as a typical example, further providing some new strategies for the vaccine development against Mhp infection.

Transcriptome sequencing analysis of porcine MDM response to FSL-1 stimulation

Mycoplasma infection can cause many diseases in pigs, resulting in great economic losses in pork production. Innate immune responses are thought to play critical roles in the pathogenesis of mycoplasma disease. However, the molecular events involved in immune responses remain to be determined. Hence, the object of this study was to use RNA-Seq to investigate the gene expression profiles of the innate immune response mediated by FSL-1 in pig monocyte-derived macrophages (MDMs). The results revealed that 1442 genes were differentially expressed in the FSL-1 group compared with the control groups, of which 777 genes were upregulated and 665 genes were downregulated. KEGG pathway analysis showed that the upregulated genes were mainly involved in innate immune-related pathways including the TNF signaling pathway, cytokine-cytokine receptor interaction, Toll-like receptor signaling pathway, Jak-STAT signaling pathway, chemokine signaling pathway, NOD-like receptor signaling pathway and NF-kappa B signaling pathway. The downregulated genes were only involved in the cGMP-PKG signaling pathway and glycerophospholipid metabolism. Our results showed that FSL-1 stimulation activated the TLR2 signaling pathway and resulted in diverse inflammatory responses. FSL-1 induced the transcription of numerous protein-coding genes involved in a complex network of innate immune-related pathways. We speculate that TNF, IL1B, IL6, NFKB1, NFKBIA, CXCL2, CXCL8, CXCL10, CCL2, CCL4 and CCL5 were the most likely hub genes that play important roles in the above pathways. This study identified the differentially expressed genes and their related signaling pathways, contributing to the comprehensive understanding of the mechanisms underlying host-pathogen interactions during mycoplasma infection and providing a reference model for further studies.

Induction of mycoplasmal pneumonia in experimentally infected pigs by means of different inoculation routes

The purpose of this study was to assess the effect of three different inoculation routes into mycoplasmal pneumonia (MP) in pigs challenged with Mycoplasma hyopneumoniae (M. hyopneumoniae). Thirty six-week-old M. hyopneumoniae seronegative piglets were randomly assigned to four groups: three challenged groups with experimentally inoculated pigs by either the endotracheal (ET; n = 8), intranasal (IN; n = 8) or aerosol (AE; n = 8) routes and one uninfected group (Control; n = 6). Blood samples were collected 1 day before challenge and at necropsy, 28 days post-inoculation (dpi), to assess seroconversion. Laryngeal swabs were collected at −1, 7, 14, 21 and 28 dpi in order to evaluate colonization. At necropsy, lung lesions were scored and lung tissue was collected for histopathological studies and M. hyopneumoniae DNA detection. Broncho-alveolar lavage fluid (BALF) was also obtained to detect M. hyopneumoniae DNA, specific IgA antibodies and cytokines. MP was observed in all inoculated groups, but the ET group displayed a significantly higher number of animals affected by MP as well as a higher mean lung lesion score. These results were paralleled with an earlier seroconversion and upper respiratory tract colonization of M. hyopneumoniae. Additionally, in the ET group, higher levels of pro-inflammatory cytokines and specific IgA antibodies in BALF were found. Under the conditions of the present study, MP was reproduced by the three evaluated inoculation routes. Obtained results suggest that the ET route is the most effective in order to induce MP in pigs experimentally challenged with M. hyopneumoniae.

Immune responses elicited by Mycoplasma hyopneumoniae recombinant antigens and DNA constructs with potential for use in vaccination against porcine enzootic pneumonia

Mycoplasma hyopneumoniae is the etiological agent of porcine enzootic pneumonia (PEP) and causes major economic losses to the pig industry worldwide. Commercially available vaccines provide only partial protection and are relatively expensive. In this study, we assessed the humoral and cellular immune responses to three recombinant antigens of M. hyopneumoniae. Immune responses to selected domains of the P46, HSP70 and MnuA antigens (P46102-253, HSP70212-601 and MnuA182-378), delivered as recombinant subunit or DNA vaccines, were evaluated in BALB/c mice. All purified recombinant antigens and two DNA vaccines, pcDNA3.1(+)/HSP70212-601 and pcDNA3.1(+)/MnuA182-378, elicited a strong humoral immune response, indicated by high IgG levels in the serum. The cellular immune response was assessed by detection of IFN-γ, IL-10 and IL-4 in splenocyte culture supernatants. The recombinant subunit and DNA vaccines induced Th1-polarized immune responses, as evidenced by increased levels of IFN-γ. All recombinant subunit vaccines and the pcDNA3.1(+)/MnuA182-378 vaccine also induced the secretion of IL-10, a Th2-type cytokine, in large quantities. The mixed Th1/Th2-type response may elicit an effective immune response against M. hyopneumoniae, suggesting that P46102-253, HSP70212-601 and MnuA182-378 are potential novel and promising targets for the development of vaccines against PEP.

Local and systemic immune responses in pigs intramuscularly injected with an inactivated Mycoplasma hyopneumoniae vaccine

The immune response induced by intramuscular administration of a commercial inactivated Mycoplasma hyopneumonie whole-cell vaccine (Suvaxyn(®)MH One) was investigated in conventional M. hyopneumoniae-free pigs. The animals were assigned randomly to two groups: non-vaccinated and vaccinated. Pigs in the vaccinated group were injected intramuscularly with the vaccine at 7 days of age, whereas non-vaccinated pigs received physiological saline solution (PBS). Pigs were euthanized and necropsied at 30, 36 and 58 days of age. Blood, bronchoalveolar lavage (BAL) fluid, spleen, lung and bronchial lymph nodes (BLN) were collected. Serum and BAL fluid were tested for the presence of antibodies by ELISA. Monomorphonuclear cells from the peripheral blood and tissues were isolated to quantify the T cell subsets by flow cytometry, and cytokine production by ELIspot and ELISA. Antibodies against M. hyopneumoniae were detected in serum of most vaccinated pigs at 30 days of age. M. hyopneumoniae specific IgG, IgM and IgA were detected in BAL fluid from vaccinated animals, but not from control animals. Significantly higher numbers of IL-12 secreting cells were observed in the lung at day 58 in the vaccinated than in the non-vaccinated group (p<0.05). The number of IL-10 secreting cells from BLN was also higher in the vaccinated group at day 58 (p<0.05). After restimulation in vitro, lymphocytes from BLN and lungs secreted significantly higher levels of IL-12 in the vaccinated group at day 58. These results show that the vaccine induced both systemic and mucosal cellular and humoral immune responses.

Vaccination reduces macrophage infiltration in bronchus-associated lymphoid tissue in pigs infected with a highly virulent Mycoplasma hyopneumoniae strain

Background

Mycoplasma hyopneumoniae is the causative agent of enzootic pneumonia and is responsible for significant economic losses to the pig industry. To better understand the mode of action of a commercial, adjuvanted, inactivated whole cell vaccine and the influence of diversity on the efficacy of vaccination, we investigated samples from vaccinated and non-vaccinated pigs experimentally infected with either a low (LV) or a highly virulent (HV) M. hyopneumoniae strain. Non-vaccinated and sham-infected control groups were included. Lung tissue samples collected at 4 and 8 weeks post infection (PI) were immunohistochemically tested for the presence of T-lymphocytes, B-lymphocytes and macrophages in the bronchus-associated lymphoid tissue (BALT). The number of M. hyopneumoniae organisms in bronchoalveolar lavage (BAL) fluid was determined using quantitative PCR at 4 and 8 weeks PI. Serum antibodies against M. hyopneumoniae were determined at 0, 2, 4, 6 and 8 weeks PI.

Results

The immunostaining revealed a lower density of macrophages in the BALT of the vaccinated groups compared to the non-vaccinated groups. The highest number of M. hyopneumoniae organisms in the BAL fluid was measured at 4 weeks PI for the HV strain and at 8 weeks PI for the LV strain. Vaccination reduced the number of organisms non-significantly, though for the HV strain the reduction was clinically more relevant than for the LV strain. At the level of the individual pigs, a higher lung lesion score was associated with more M. hyopneumoniae organisms in the lungs and a higher density of the investigated immune cells in the BALT.

Conclusions

In conclusion, the infiltration of macrophages after infection with M. hyopneumoniae is reduced by vaccination. The M. hyopneumoniae replication in the lungs is also reduced in vaccinated pigs, though the HV strain is inhibited more than the LV strain.

Effect of cross-fostering on transfer of maternal immunity to Mycoplasma hyopneumoniae to piglets

The aim of this study was to assess the effect of cross-fostering on transfer of maternal Mycoplasma hyopneumoniae-specific humoral and cell-mediated immunity (CMI) from gilts to piglets. Cross-fostering, carried out within gilt pairs, was based on the gilts' M hyopneumoniae vaccination status in accordance with the following scheme: six pairs of vaccinated gilt × non-vaccinated gilt (V × N); five pairs of non-vaccinated gilt × vaccinated gilt (N × V); and five pairs of vaccinated gilt × vaccinated gilt (V × V). The piglets were cross-fostered at 0, six, 12 or 20 hours after birth. Two piglets per gilt per time point were cross-fostered (that is, eight piglets per gilt were moved) and the remaining piglets served as non-cross-fostered controls. In addition, four litters served as non-cross-fostered controls. A maximum of 10 piglets per gilt were sampled. The piglets' M hyopneumoniae-specific humoral immunity was assessed by ELISA and their CMI was assessed by delayed-type hypersensitivity testing. M hyopneumoniae-specific antibodies were detected in non-cross-fostered piglets from vaccinated dams and from piglets cross-fostered within the V × N gilt pair at six hours or more, and within the V × V gilt pair at all time points. Piglets cross-fostered within the N × V gilt pair had detectable M hyopneumoniae-specific antibodies only if they had been moved within six hours of birth. The transfer of M hyopneumoniae-specific CMI to piglets appeared to be source-dependent, and was detected only in piglets maintained on their vaccinated dams for at least 12 hours after birth.

Immune responses induced by replication-defective adenovirus expressing the C-terminal portion of the Mycoplasma hyopneumoniae P97 adhesin

Mycoplasma hyopneumoniae, the causative agent of porcine enzootic pneumonia, colonizes the respiratory cilia of affected swine, causing significant economic losses to swine production worldwide. Vaccination is the most cost-effective strategy for the control and prevention of this disease. The goal of this study was to design and evaluate a replication-defective recombinant adenovirus, rAdP97c, expressing the C-terminal portion of P97 adhesin (P97c), an important pathogenesis-associated protein of M. hyopneumoniae, as a new vaccine candidate against M. hyopneumoniae infection. P97c-specific immune responses were evaluated in BALB/c mice following intranasal and intramuscular inoculation with rAdP97c. Mice inoculated by both routes of immunization produced significant levels of specific immunoglobulin G (IgG) antibodies in the serum and in bronchoalveolar lavage fluids (BALs). Animals immunized intranasally also produced a significant level of P97c-specific IgA in BALs. Intramuscular inoculation of rAdP97c induced a systemic and mucosal Th1-type biased response, evidenced by the predominance of IgG2a in the serum and BALs, whereas intranasal inoculation resulted in a mixed Th1/Th2-type response (balanced levels of IgG1 and IgG2a) in both sytemic and mucosal compartments. P97c-specific antibodies were able to inhibit the growth of M. hyopneumoniae cells in vitro. These data suggest that rAdP97c vaccine may represent a new strategy for controlling infection by M. hyopneumoniae.

Detection of Mycoplasma hyopneumoniae in lung and nasal swab samples from pigs by nested PCR and culture methods

We examined nasal swab and lung homogenate samples collected from pigs experimentally and naturally infected with Mycoplasma hyopneumoniae for the detection of M. hyopneumoniae by the nested PCR (nPCR) and culture methods. In the 23 experimentally infected pigs, M. hyopneumoniae was commonly detected in nasal swabs by the nPCR and culture methods at 4 weeks after inoculation, and there was a significant correlation (P<0.01) between the titers of viable organisms in nasal swabs and in lung homogenates in the experimentally inoculated pigs. In the naturally infected pigs, on the other hand, discrepancies in detection were found between nasal swab and lung homogenate samples in 17 of 36 cases, although the presence of gross lung lesions correlated relatively well with the detection of organisms from the samples. Our results indicated that the diagnosis of mycoplasmal pneumonia by nPCR in individual pigs with nasal swabs is reliable under these experimental conditions. At present, nPCR with nasal swabs should only be used for monitoring the disease status at the herd level under field conditions.

Septicaemia and arthritis in pigs experimentally infected with Pasteurella multocida capsular serotype A

Twenty-five caesarean-derived, colostrum-deprived (CDCD) pigs and 18 specific pathogen-free pigs, aged 8 to 14 weeks, were inoculated intranasally or intratracheally with Pasteurella multocida capsular serotype A, isolated from a severe pneumonic lesion in a growing pig. The pigs were killed for necropsy on day 6 or 14 post-inoculation (PI) or, in the case of the only fatally infected animal, examined at the time of death. One CDCD pig, inoculated intratracheally with 5 ml of a bacterial suspension containing 1.7x10(9) colony-forming-units/ml, died of septicaemia on day 1 PI. Histological lesions such as severe pleuropneumonia, thrombi in glomerular capillaries, haemorrhage of the spleen, and abscesses in the tonsillar crypts were observed. The organism was recovered from a number of sites and its antigens were detected immunohistochemically in the pneumonic lesions, blood vessels of the tissues, and tonsillar crypts in the dead pig. Pneumonia, pleural adhesions and suppurative arthritis in the extremital joints were observed grossly in 3/29, 8/29 and 7/29 intratracheally inoculated pigs, respectively. In intranasally inoculated pigs, no macroscopical abnormalities were seen; histologically, however, exudative bronchopneumonia and fibrinous pleurisy were observed in 9/14 and 4/14 pigs, respectively. No significant changes were seen in the tissues of uninfected control pigs. The organism was recovered from the lesions and P. multocida type A antigen was demonstrated immunohistochemically. The organism was rarely recovered from the liver, spleen or lymph nodes (bronchopulmonary or mesenteric). The results suggest that P. multocida capsular serotype A alone can cause not only pneumonia in pigs but also septicaemia or arthritis.

A morphologic and immunohistochemical study of the bronchus-associated lymphoid tissue of pigs naturally infected with Mycoplasma hyopneumoniae

Porcine enzootic pneumonia (PEN), caused by Mycoplasma hyopneumoniae (Mh), has been described in pigs in all geographic areas. The disease is characterized by high morbidity and low mortality rates in intensive swine production systems. A morphologic and immunohistochemical study was done to determine the cellular populations present in lung parenchyma of infected pigs, with special attention to the bronchus-associated lymphoid tissue (BALT). Polyclonal and monoclonal antibodies were used for the detection of antigens of Mh, T lymphocytes (CD3+, CD4+, and CD8+), IgG+ or IgA+ lymphocytes, and cells containing lysozyme, S-100 protein, major histocompatibility complex class II antigen or myeloid-histiocyte antigen. Findings in lung tissues associated with Mh infection were catarrhal bronchointerstitial pneumonia, with infiltration of inflammatory cells in the lamina propria of bronchi and bronchioles and alveolar septa. Hyperplasia of mononuclear cells in the BALT areas was the most significant histologic change. The BALT showed a high morphologic and cellular organization. Macrophages and B lymphocytes were the main cellular components of germinal centers. T lymphocytes were primarily located in perifollicular areas of the BALT, lamina propria and within the airway epithelium, and plasma cells containing IgG or IgA at the periphery of the BALT, in the lamina propria of bronchi and bronchioles, in alveolar septa, and around bronchial submucosal glands. The hyperplastic BALT in PEN cases consisted of macrophages, dendritic cells, T and B lymphocytes, and IgG+ and IgA+ plasma cells. CD4+ cells predominated over CD8+ cells. Local humoral immunity appears to play an important role in the infection.

Protective effects of oral microencapsulated Mycoplasma hyopneumoniae vaccine prepared by co-spray drying method

The efficacy of Mycoplasma hyopneumoniae oral vaccine was investigated in microsphere dosage form. A co-spray drying process was used to apply an encapsulating material, Eudragit L30 D-55, to microspheres containing Mycoplasma hyopneumoniae antigens. The microspheres were generally effective (>93%) with protein release at pH 7.4, but almost none were released at pH 1.2, for 3 hr in an in vitro dissolution test. An SPF-swine model was used to evaluate the effectiveness of the microspheres as an oral vaccine, and the related immune responses. The serum's systemic IgG against M. hyopneumoniae was evoked by ELISA analysis, after a 2nd immunization of all pigs. The vaccinated groups' mean lesion score was significantly lower after the Mycoplasma hyopneumoniae challenge than that of the nonvaccinated/challenged groups (P<0.05). This study strongly suggests that the oral microspheres vaccine prepared by a co-spray drying method can provide effective protection against M. hyopneumoniae infection in pigs.

Perivascular capillaries in the lung: an important but neglected vascular bed in immune reactions?

In allergic and inflammatory immune reactions of the respiratory tract, leukocytes migrate into the different compartments of the lung. The air space can easily be sampled by means of bronchoalveolar lavage. However, the subset composition in the bronchial wall or the lung interstitium often differs considerably from that of the bronchoalveolar lavage fluid. A further compartment involved in very heterogeneous immune reactions in the lung has thus far not been mentioned: the periarterial space. In numerous experiments in different species with virus, bacteria, fungi, or allergens, there was not only a leukocyte infiltration of the bronchial lamina propria but also infiltration around branches of the pulmonary artery. This thus far neglected compartment consists of a different type of capillary. Thus it is important not to overlook this area in studies on allergic or inflammatory immune reactions of the lung.

In vivo and in vitro comparisons of spray-drying and solvent- evaporation preparation of microencapsulated Mycoplasma hyopneumoniae for use as an orally administered vaccine for pigs

OBJECTIVE

To evaluate the efficacy of an orally administered vaccine of Mycoplasma hyopneumoniae that was prepared by spray drying or solvent evaporation.

ANIMALS

Thirty 6-week-old, crossbred, specific-pathogen-free (SPF) pigs.

PROCEDURE

Pigs were randomly allocated into 5 groups and housed in an SPF facility. Pigs in 2 groups (groups AQ and CAP) were fed M hyopneumoniae enteric-coated vaccine on days 0, 10, and 20. A third group (group IM) received an IM injection of M hyopneumoniae vaccine with aluminium hydroxide as an adjuvant on days 0, 10, and 20. The last 2 groups (non-vaccinated-challenged [NV-C] and nonchallenged [NC]) were fed a sham treatment. All 24 pigs in groups AQ, CAFP IM, and NV-C were challenge exposed with 5 ml of a 10% pneumonic lung suspension administered on day 40 via intubation of the trachea. All pigs were slaughtered and the lungs removed and examined for lesions on day 68.

RESULTS

In vitro studies indicated that these 2 microencapsulation techniques formed an effective shell and protected mycoplasmal antigen from gastric acid. Results of inoculation and challenge tests indicated that microencapsulated M hyopneumoniae were sufficiently potent to induce an immune response and provide good protection.

CONCLUSIONS AND CLINICAL RELEVANCE

Orally administered microencapsulated M hyopneumoniae vaccines induced an immune response and reduced the severity of lung lesions in challenge-exposed pigs. Results suggest that this novel method can be applied to other antigens, because the spray-drying process yielded an orally administered M hyopneumoniae vaccine that induced a good immune response.