An experimental mouse model of progressive atrophic rhinitis of swine

Pathogenicity, colonization, and innate immune response to Pasteurella multocida in rabbits

BACKGROUND

Pasteurella multocida (P. multocida) infection can cause a series of diseases in different animals and cause huge economic losses to the breeding industry. P. multocida is considered to be one of the most significant pathogens in rabbits. In order to elucidate the pathogenic mechanism and innate immune response of P. multocida, an infection experiment was carried out in this study.

RESULTS

Our results showed that the clinical symptoms of rabbits were severe dyspnoea and serous nasal fluid. During the course of the disease, the deaths peaked at 2 days post infection (dpi) and mortality rate was 60%. The pathological changes of the lung, trachea, and thymus were observed. In particular, consolidation and abscesses appeared in lung. Histopathologic changes in rabbits showed edema, hemorrhage, and neutrophil infiltration in the lung. P. multocida can rapidly replicate in a variety of tissues, and the colonization in most of the tested tissues reached the maximum at 2 dpi and then decreased at 3 dpi. The number of P. multocida in lung and thymus remained high level at 3 dpi. Toll-like receptors 2 and 4 signaling pathways were activated after P. multocida infection. The expression of Il1β, Il6, Il8, and Tnf-α was significantly increased. The expression of most proinflammatory cytokines peaked at 2 dpi and decreased at 3 dpi, and the expression trend of cytokines was consistent with the colonization of P. multocida in rabbit tissues.

CONCLUSIONS

The P. multocida can rapidly replicate in various tissues of rabbit and cause bacteremia after infection. TLRs signaling pathways were activated after P. multocida infection, significantly inducing the expression of proinflammatory cytokines, which is might the main cause of respiratory inflammation and septicemia.

The effect of carbohydrates on the adherence of Pasteurella multocida to the nasal respiratory epithelium

Pasteurella multocida subsp. multocida is responsible for different diseases that generate great economic losses in farm animal. The effectiveness of immunization against those bacteria are variable and the use of antibiotics is questioned; for that reason, we investigated the potential inhibitory effect of different carbohydrates on the adherence in vivo of P. multocida to the rabbit respiratory epithelium as an alternative for the prevention of respiratory infections. Rabbits were intranasally and intratracheally inoculated with a solution containing 200 µl of 1x107 CFU of P. multocida that was previously mixed with 250 µg /200 µl of N-acetylglucosamine, alphamethylglucoside, alphamethylmannoside, N-acetylgalactosamine or sialic acid. The animals that received N-acetylglucosamine, alphamethylglucoside or alphamethylmannoside individually or a mixture of these three carbohydrates plus the bacterium, showed a significant decrease (P <0.05) of the clinical symptoms, microscopic and macroscopic lesions in the nasal septa and in the lungs; also, the number of adhered bacteria to the nasal epithelium were also significantly reduced. This research demonstrates for the first time that such an approach could convert into a method for prevention of P. multocida infection in rabbits that is ecologically and economically safe and effective.

Generation of porcine Pasteurella multocida ghost vaccine and examination of its immunogenicity against virulent challenge in mice

Pasteurella multocida (PM) causes a varity of clinical manifestation in domestic animals, even acute death. Vaccination is among effective strategy to prevent and control PM-related diseases. Bacterial ghosts (BGs) are empty bacterial envelopes, which sustain subtle antigenic comformation in bacterial outer-membrane and exhibit higher efficacy compared to inactivated vaccines. Here, a BG vaccine generated from the porcine PM reference strain CVCC446 (serotype B:2) was prepared upon lysis by E protein of bacteriophage PhiX174, and the safety and immunogenicity were evaluated its in a mouse model. Lysis rate was in 99.99% and the BG vaccine was completely inactivated by addition of freeze-dry procedure. Mice were immunized subcutaneously twice in 2-week intervals with BGs, or BGs plus adjuvant, or formalin-inactivated PM or an adjuvant control. Mice inoculated twice with BGs vaccines generated higher titer of antibodies, interleukin 4 and gamma interferon than those in the inactivated vaccine group or adjuvant placebo group (P < 0.05). CD4⁺ and CD8⁺ T lymphocyte levels in spleen were higher in both BG groups than inactivated vaccine group or adjuvant group. Mice administered with the BGs plus adjuvant were completely protected against intraperitoneal challenge with 10 × LD₅₀ dose of virulent isolate and exhibited decreased tissue lesion and lower bacterial loads, which was superior to the inactivated vaccine. The results demonstrated safety of the BG vaccine and primary immunogenicity in a mouse model, suggesting a potential of further evaluation in a pig model and vaccine candidate.

Is submucosal fat injection effective in atrophic rhinitis? An experimental animal study

Atrophic rhinitis (AR) is a disease characterized by the extensive dilatation of the nasal cavity and atrophy of the mucosa, submucosa and bone tissue. Its etiological factors are unknown. There is not a satisfying treatment yet and the treatment of the functional impairment in the atrophic cells is still subject to investigation. The objective of this study is to determine at the histopathological level the possible effects of the submucosal fat injection in an experimental model of AR. 12 albino Wistar-Hannover male rats were included in the study. AR was induced with the Pasteurella multocida toxin, which was diluted with saline. As one of the rats died during the study, it was excluded from the evaluation. The right nasal cavities of all rats (11 nasal cavities) were defined as the control group (Group 1). Fat tissue obtained from the abdominal area was injected in the seven left nasal cavities (Group 2). All injections, which were done to the abdominal regions were also done in the left nasal cavities of the remaining four rats, which constituted the sham group (Group 3). After 14 days, all rats were decapitated and the squamous metaplasia and keratinization in the superficial epithelium, degeneration, vacuolar changes in the basal layer, congestion, inflammatory infiltration, vascular proliferation and glandular atrophy in the submucosa are histopathologically classified. The results were analyzed with statistical methods. Although glandular atrophy was significantly regressed in the fat injection group (Group 2) compared to other groups (p < 0.05), the remaining parameters did not show any significant difference among these three groups. The histopathological effect of the fat injection was modest. We concluded that fat injection treatment has no or at the most a very limited effect in the treatment of atrophic rhinitis.

Pasteurella multocida: diseases and pathogenesis

Pasteurella multocida is an enigmatic pathogen. It is remarkable both for the number and range of specific disease syndromes with which it is associated, and the wide range of host species affected. The pathogenic mechanisms involved in causing the different syndromes are, for the most part, poorly understood or completely unknown. The biochemical and serological properties of some organisms responsible for quite different syndromes appear to be similar. Thus, the molecular basis for host predilection remains unknown. The recent development of genetic manipulation systems together with the availability of multiple genome sequences should help to explain the association of particular pathological conditions with particular hosts as well as helping to elucidate pathogenic mechanisms.