Comparison of immunity induced with a Mycoplasma gallisepticum bacterin between high- and low-responder lines of chickens.

Chickens of the high-responder line GSP and low-responder line BM-C, which had been known to have different antibody responses to Mycoplasma gallisepticum (MG) antigen, were immunized by intramuscular injection and by subsequent intratracheal instillation of MG bacterin. They were then challenged with the pathogenic strain SAS of MG. The preventive effects of local antibodies detectable in the trachea, saliva, and lacrima were compared between the two lines of chickens. The local antibody responses, as determined by an enzyme-linked immunosorbent assay, were higher in line GSP than in line BM-C before and after challenge. Following challenge, chickens of both lines were protected from colonization by MG and the development of respiratory lesions. The degree of protection in line GSP was higher than that of line BM-C. The results suggest that local antibodies may play an important role in the host defense mechanism to respiratory MG infection.     

Efficacy of commercial Mycoplasma gallisepticum bacterin (MG-Bac) in preventing air-sac lesions in chickens

One-week-old chickens were vaccinated with commercial Mycoplasma gallisepticum bacterin subcutaneously and challenged with the S6 strain by the intra-air-sac route 3 weeks later. Significantly fewer vaccinated chickens had air-sac lesions than controls.     

Effect of Mycoplasma gallisepticum bacterin on egg-transmission and egg production

Groups of white leghorn hens were vaccinated twice with a Mycoplasma gallisepticum (MG) bacterin, once with bacterin, or left unvaccinated. Four weeks after vaccination, they were challenged with virulent R strain MG. Egg production was significantly higher in challenged vaccinated groups than in the challenged control group. Four challenged control hens went out of production, whereas only one twice-vaccinated hen did. MG was first isolated directly from eggs 5 days postchallenge (PC) in twice-vaccinated hens, 4 days PC in once-vaccinated hens, and 2 days PC in controls, and the hens continued to lay positive eggs till the end of the experiment 7 weeks PC. MG was found in 17.65%, 38.55%, and 45.90% of eggs cultured in twice-vaccinated, once-vaccinated, and control groups, respectively. Nine of 16 twice-vaccinated hens were found to be shedding MG through their eggs, whereas 15 of 17 once-vaccinated hens and 14 of 16 controls were shedding MG through their eggs.     

Efficacy of experimental inactivated mycoplasma gallisepticum oil-emulsion bacterin in egg-layer chickens

Six groups of white leghorn pullets were studied to determine the ability of beta-propiolactone-inactivated Mycoplasma gallisepticum (MG) oil-emulsion bacterins to counteract reductions in egg production caused by MG infection. The pullets were inoculated with 0.5 ml of MG bacterin subcutaneously in the neck at about 20 weeks of age and were challenged with MG near 28 weeks of age, when they were in peak egg production. Various challenge schemes with infectious bronchitis virus were used at the time of MG challenge to increase the reduction in egg production. MG bacterins afforded protection against moderate drops in egg production in at least three of the studies, where the unvaccinated challenged control hens exhibited reduced egg production.     

Immunization of chickens with temperature-sensitive mutants of Mycoplasma gallisepticum

Temperature-sensitive (TS) mutants of the S6 strain of Mycoplasma gallisepticum (MG) were used to immunize newly hatched chickens. Immunized chickens developed antibodies to the wild-type (WT) S6 strain as demonstrated by serologic tests. MG was recovered from nasal cavities but not from the lower respiratory tract of the immunized chicks. Three weeks after intranasal immunization, chickens were challenged via the air sacs with the virulent S6 strain. Immunized chickens were significantly better protected from development of air-sac lesions than were controls.     

鸡败血支原体接种鸡体液免疫的变化规律

SPF鸡接种鸡败血支原体R株、F株和油乳剂苗后，用ELISA检测IgM、IgG和IgA的变化规律，发现特异性IgM出现时间存在差异；强毒株感染后IgM始终存在，因此可作为临诊感染的指证。油乳剂苗能产生IgA，证明油乳剂苗能诱导产生局部免疫。     

Disposition kinetics of doxycycline in chickens naturally infected with Mycoplasma gallisepticum

1. The pharmacokinetic properties of doxycycline were determined in healthy chickens and chickens naturally infected with Mycoplasma gallisepticum after a single intravenous (i.v.) and oral administration of the drug at 20 mg/kg body weight. Tissue residues of the tested drug after an oral dose of 20 mg/kg given twice daily for 5 consecutive days were also estimated in diseased chickens. 2. The plasma concentrations of doxycycline following single i.v. and oral administration were higher in healthy chickens than in diseased ones. Following i.v. injection, the elimination half-life (t1/2beta), distribution half-life and mean residence time (MRT) were longer in healthy chickens than in diseased birds. The values of total body clearance (ClB) and volume of distribution (Vdss) were larger in healthy chickens than in diseased birds. 3. After single oral administration, the absorption half-life (tl/2ab) and the elimination half-life were longer in normal birds than in diseased ones. The maximum plasma concentration of the drug was higher in normal chickens than in diseased ones. 4. Following repeated oral administration, the concentration of doxycycline in all tissues except muscle was higher than the corresponding concentrations in plasma. Concentrations of doxycycline in different tissues were in the following order: kidney > liver > lung > muscle. The drug was detected in liver and kidney in substantial concentrations on d 5 post administration of the last dose whereas, on d 7, its concentration in all tissues was below the lower limit of the sensitivity of the assay method used. Because of the low sensitivity of the microbiological assay method used in this study, a safe withdrawal time for doxycycline in diseased birds could not be estimated for the meanwhile.     

藏鸡鸡毒霉形体的血清学调查

霉形体又称支原体 ,是一类缺乏细胞壁的原核微生物 ,分类学上属于软皮纲成员。在兽医学上是一类重要的病原微生物 ,对禽类等动物具有广泛的致病性。 2 0 0 2年 4月 ,西藏某些地区鸡发生一种以咳嗽 ,鼻炎 ,打喷嚏 ,呼吸有锣音等呼吸症状为主要特征的疾病。另外 ,还可见到鼻分泌物较多 ,部分鸡出现结膜炎 ,眼中伴有泡沫分泌物 ,产蛋量下降并有死亡现象。经血清学快速诊断为鸡毒霉形体。为了摸清鸡毒霉形体在藏鸡中的感染情况 ,我们应用血清学方法对西藏各地区的藏鸡进行霉形体检测。结果显示我区藏鸡的鸡毒霉形体感染率较高 ,对藏鸡的年龄、性…     

Monitoring Mycoplasma gallisepticum and Mycoplasma synoviae infection in breeder chickens after treatment with enrofloxacin.

Three experimental strains of breeder chickens were accidentally exposed to Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS), presumably from a newly introduced group of leghorn-type pullets. The experimental strains subsequently became infected and were diagnosed positive for MG and MS by the serum plate agglutination (SPA) test and confirmed by the hemagglutination inhibition (HI) test and the polymerase chain reaction (PCR) of tracheal swabs. Treatment with 10 mg/kg enrofloxacin via drinking water for 14 days was elected. Before and after initiation of treatment, MG and MS were monitored for changes by SPA, HI, PCR, and culture, with sampling intervals ranging from 1 wk to 7 wk. MG and MS SPA, HI, PCR, and culture were performed at each sampling period, with the exception of weeks 1.0 and 6.5. Week 1.0 included SPA and His for MG and MS. Week 6.5 included PCR and culture for MG and MS. The MG and MS SPA results were positive throughout the 29-wk trial period. MG HI titers declined until the last sampling, whereas the MS HI titers did not decline significantly. PCR for MG yielded only one positive result, which occurred before treatment. MS PCR remained positive throughout the trial period. MG was never isolated from any sample; however, one MS organism was isolated during treatment. The treatment regimen was effective for MG on the basis of PCR results. Treatment with enrofloxacin did not eliminate SPA reactions during the 29-wk trial period. MG HI titers remained in the suspicious range throughout the remainder of the trial period. Four weeks after the treatment ended, MG HIs were reduced by approximately 40%, with MS HIs remaining high throughout the 29-wk period. PCR appeared to be a sensitive and specific test on the basis of correlation with HIs. On the basis of the isolation of MS during treatment and continued subsequent PCR positive reactions, the treatment for MS with enrofloxacin was not as efficacious as for MG.     

Antibody responses in sera and respiratory secretions from chickens infected with Mycoplasma gallisepticum

Antibodies in sera and respiratory secretions from chickens infected with Mycoplasma gallisepticum (MG) were measured by an enzyme-linked immunosorbent assay (ELISA). Chickens intratracheally inoculated with 10(5) cells of MG showed a correlation between severity of tracheal lesions and extent of MG colonization in the tracheas in the first 3 weeks postinoculation. Antibody titers in tracheal washings (TWs) of the infected chickens increased during this phase. Thereafter, isolation of MG from the trachea decreased sharply, and there was a concomitant decrease in tracheal lesion scores. At 5 weeks postinfection, the chickens that recovered from the infection exhibited a consistent presence of antibodies in TWs. Chickens reexposed had a faster rate of MG elimination and substantially less severe inflammatory lesions in the tracheas than chickens observed after the first exposure. These findings suggest a possible role of antibodies of the respiratory secretions in resistance to MG. The ELISA was a sensitive and reliable test to detect a minute amount of antibodies in the secretions.     

Response of chickens to inoculation with a temperature-sensitive mutant of Mycoplasma gallisepticum

Newly hatched chickens were inoculated intranasally with either the S6 or TS 100 strain of Mycoplasma gallisepticum (MG) or they were left uninoculated. The three groups of chickens did not differ discernibly in body, spleen, or bursa weight during the 27-day sampling period. However, the S6-inoculated chickens showed a more pronounced cellular response in the nasal passages and had nearly complete lymphoid depletion in the spleens. The TS 100-inoculated birds expressed only a mild cellular reaction, which was localized in the nasal passages. Uninoculated chickens appeared normal histologically. Serologic tests such as rapid serum plate agglutination, hemagglutination-inhibition, and radioimmunoassay were able to detect antibody responses of chickens to MG inoculations yet could not differentiate the response to TS 100 from the response to S6. Tracheal secretions in intact TS 100-inoculated chickens contained antibodies to MG, yet only one-half of the bursectomized inoculated chickens contained detectable antibody, which appeared to be IgG. This led to the conclusion that bursectomy suppresses the appearance of locally synthesized IgG antibodies to MG in tracheal washings. The locally produced antibody was considered important in the development of resistance induced by intranasal inoculation of TS mutants.     

Evaluation of protection against Mycoplasma gallisepticum infection in chickens vaccinated with the F strain of M. gallisepticum

The effect of vaccination with the F strain of Mycoplasma gallisepticum (MG) on protection against challenge with a tylosin-resistant strain of MG was evaluated. White leghorn chickens vaccinated via eyedrop at 6 weeks of age were subsequently challenged with various dilutions of the tylosin-resistant MG strain, as were unvaccinated controls. Three days later, tracheal swabs were collected and cultured in medium with and without tylosin to distinguish between the vaccine and challenge strains. The mean infectious dose of the challenge strains was 3.8 log10 higher in the vaccinated group than in the controls, and the vaccinated group harbored fewer challenge organisms in the trachea. These findings suggest that the F strain of MG induces protection against infection with field strains of MG and that long-term vaccination with the F strain in multiple-age layer farms may result in replacement of field MG strains by the F strain.     

Further studies on the immunization of chickens with temperature-sensitive Mycoplasma gallisepticum mutant

Newly hatched chickens were immunized with a temperature-sensitive (TS) Mycoplasma gallisepticum (MG) mutant (TS 100). Immunized chickens resisted challenge with the virulent S6 strain. The dose of TS MG needed for protection was less than 3.3 X 10(4) colony-forming units. After immunization with TS 100, chickens were subjected to a variety of virus infection and immunosuppressive treatments. Neonatal bursectomy or thymectomy, infectious bursal disease virus infection, and infectious bronchitis virus vaccination or a combination of infectious bronchitis virus and Newcastle disease virus vaccination did not contribute to the development of air-sac lesions in TS MG-immunized chickens. Infectious bronchitis virus vaccination enabled MG to migrate from the nasal cavity to the trachea but not to the air sacs. The TS MG vaccine appears to be a safe immunogen.     

DNA probes for Mycoplasma gallisepticum and Mycoplasma synoviae: application in experimentally infected chickens

DNA probes specific for Mycoplasma gallisepticum and M. synoviae were selected from genomic libraries prepared in the pUC13 vector. The probes hybridized with the DNA of a wide spectrum of strains within each homologous species, but did not react with the heterologous species or with DNA from any other avian mycoplasma or bacteria tested. Experimental infection and contact exposure of chickens to M. gallisepticum served as models to test the effectiveness of the DNA probe in diagnosis as compared with serological and culture detection methods carried out in parallel. A correlation was generally found between the level of M. gallisepticum in tracheal swabs and the effectiveness of the probe, although a predictably reactive level of mycoplasmas was not always detected. Treatment of clinical specimens with acetylcysteine to disrupt mucus improved the detection rate. Dot-blot hybridization with probe pMG4 enabled positive identification of M. gallisepticum at an early stage of infection, prior to the development of a serological response in the infected chicken. Results are obtainable within 4 days of sampling, much more rapidly than culture, and also in clinical specimens from which mycoplasma isolation is impossible, such as carcasses. The results indicate that the use of DNA probes for the early and rapid detection of M. gallisepticum infection is feasible; a development which can replace laborious culture techniques and less effective serological methods, and thus reduce the time required for diagnosis.     

Evaluation of Mycoplasma gallisepticum K-strain as a live vaccine in chickens

We evaluated the pathogenicity of three live Mycoplasma gallisepticum (MG) vaccine candidates by infection via aerosol of 3-wk-old chickens with log phase broth cultures (trial 1). Two of the candidates (K3020 and K4649A) colonized only 10% and 20% of the chickens, respectively, unlike K2101 (K-strain), which was reisolated from all of the vaccinated chickens tested. K-strain inoculation did not result in significant air sac or tracheal lesions in chickens at 10 and 39 days postinfection (P < or = 0.05). The efficacy of K-strain as a live vaccine was evaluated in trial 2, by challenge of vaccinated chickens with virulent R-strain via aerosol at 6 wk postvaccination. K-strain vaccination resulted in significant protection from air sac and tracheal lesions (P < or = 0.05). The K-strain was further investigated to evaluate transmissibility (trial 3), colonization and persistence of infection following aerosol administration (trial 4), genetic and phenotypic stability following back passage through chickens (trial 5), and vertical transmission (trial 6). The K-strain had a low rate of horizontal transmission; it remained primarily in the respiratory system of inoculated birds and persisted in the upper respiratory tract for the duration of the trial 4 (5 mo). There was no increase in virulence of K-strain when it was back passaged five times through chickens, and no vertical transmission of K-strain was detected. K-strain showed great potential as a safe and effective live MG vaccine.