The effect of a live vaccine on the horizontal transmission of Mycoplasma gallisepticum

Quantification of the effect of vaccination on the control of horizontal transmission of Mycoplasma synoviae under field conditions

Beside biosecurity, vaccination is important for Mycoplasma synoviae (MS) control as it has been shown to contribute to the reduction of economic impact and, experimentally, also lessens horizontal transmission. In this study, the effect of MS live vaccination on horizontal transmission was quantified under field conditions by analysing 4-year MS monitoring data from non-MS-vaccinated broiler and layer breeders and MS-vaccinated broiler breeders with good biosecurity in single-age housing systems. Flocks were monitored at 20 and 30 weeks of age and every 12 weeks thereafter. At every sampling, 60 blood samples or 24 tracheal swabs were tested using rapid plate agglutination test and ELISA serially or MS DIVA PCR, respectively. The MS incidence rate was calculated and the association with vaccination was analysed by logistic regression. The average MS incidence rate per 1000 weeks was 11.6 cases for non-MS-vaccinated broiler breeders and decreased from 29.6 to 5.6 cases with successive vaccinated production cycles. In non-MS-vaccinated layer breeders it was 3.6. A significant negative association with MS incidence was found after vaccinating four to six successive production cycles compared to non-MS-vaccinated or only one production cycle vaccinated breeders (odds ratio (OR) = 0.23, P = 0.05 & OR = 0.12, P = 0.01, respectively). A significant negative association with MS in non-MS-vaccinated layer breeders (OR = 0.29, P = 0.00) was observed compared to non-MS-vaccinated broiler breeders, possibly due to more controlled contact structures within the layer breeder industry. The results suggest that vaccination and control of contacts contribute to the reduction of between-farm MS transmission.

Molecular characterization and antimicrobial susceptibility profiles of Thai Mycoplasma synoviae isolates

Mycoplasma synoviae (MS) infection is mainly controlled by pathogen-free flocks' maintenance, medication in infected flocks, and vaccination in high-risk flocks. The effective control strategy requires convenient approach for detecting and differentiating MS strains and reliable drug susceptible evidence for deciding on reasonable antimicrobial usage. This study aimed to characterize the partial vlhA gene of nine Thai MS isolates circulated in chickens in 2020, to verify the PCR-RFLP assay for strain differentiation, and to determine the eight antimicrobial susceptibility profiles using microbroth dilution method. Based on sequence analysis of the partial vlhA gene, Thai MS isolates in 2020 were classified as types E and L with 19 and 35 amino acid lengths, respectively. The developed PCR-RFLP assay could detect and differentiate vaccine and Thai field strains. Most Thai MS isolates in this study were susceptible to tylosin, tylvalosin, tiamulin, doxycycline, oxytetracycline, tilmicosin, and lincomycin-spectinomycin at MIC₅₀ values of 0.0391, 0.0098, 0.0781, 0.1563, 0.1563, 0.625 and 0.625 μg/mL, respectively; and resistance to enrofloxacin at MIC₅₀ value of 10 μg/mL. In conclusion, this study revealed diagnostic assays for differentiating MS strains and the antimicrobial susceptibility profiles of Thai MS, which are necessary to design suitable MS control procedures for poultry flocks.

CHANGES IN TISSUE TROPISM OF MYCOPLASMA GALLISEPTICUM FOLLOWING HOST JUMP

Mycoplasma gallisepticum, a pathogen of worldwide economic importance in poultry, is recovered in chickens, especially from the respiratory tract. Some strains, however, are specialized to other tissues and because it jumps from poultry to wild birds, the new strains also cause severe conjunctivitis in new hosts. Nevertheless, most studies of M. gallisepticum in wild birds use choanal swabs or combine choanal and conjunctival swabs to quantify bacterial load. Because the clinical signs associated with M. gallisepticum infection differ markedly between poultry and House Finches (Haemorhous mexicanus), we compared the bacterial load in choanal and conjunctival samples following experimental inoculation of House Finches with M. gallisepticum isolates originating from poultry or from House Finches. This allowed us to test two hypotheses: M. gallisepticum changed tissue tropism, or M. gallisepticum simply expanded its within-host niche. By comparing bacterial loads from choanal and conjunctival swabs in birds inoculated with one of a suite of M. gallisepticum isolates, we found support for hypothesis 2. The choanal loads in House Finches did not differ between isolates, while the conjunctival loads of birds inoculated with poultry isolates were lower than in birds inoculated with House Finch isolates. When measuring the bacterial load of M. gallisepticum in birds, it is important to sample and analyze separately choanal and conjunctival swabs, as quantifying bacterial loads in pooled samples may not provide reliable information on differences in virulence.

Prudent Use of Tylosin for Treatment of Mycoplasma gallisepticum Based on Its Clinical Breakpoint and Lung Microbiota Shift

The aim of this study was to explore the prudent use of tylosin for the treatment of chronic respiratory infectious diseases in chickens caused by Mycoplasma gallisepticum (MG) based on its clinical breakpoint (CBP) and its effect on lung microbiota. The CBP was established based on the wild-type/epidemiological cutoff value (CO_WT/ECV), pharmacokinetics-pharmacodynamics (PK-PD) cutoff value (CO_PD), and clinical cutoff value (CO_CL) of tylosin against MG. The minimum inhibitory concentration (MIC) of tylosin against 111 MG isolates was analyzed and the CO_WT was 2 μg/ml. M17 with MIC of 2 μg/ml was selected as a representative strain for the PK-PD study. The CO_PD of tylosin against MG was 1 μg/ml. The dosage regimen formulated by the PK-PD study was 3 days administration of tylosin at a dose of 45.88 mg/kg b.w. with a 24-h interval. Five different MIC MGs were selected for clinical trial, and the CO_CL of tylosin against MG was 0.5 μg/ml. According to the CLSI decision tree, the CBP of tylosin against MG was set up as 2 μg/ml. The effect of tylosin on lung microbiota of MG-infected chickens was analyzed by 16S rRNA gene sequencing. Significant change of the lung microbiota was observed in the infection group and treatment group based on the principal coordinate analysis and the Venn diagrams of the core and unique OTU. The phyla Firmicutes and Proteobacteria showed difference after MG infection and treatment. This study established the CBP of tylosin against MG. It also provided scientific data for the prudent use of tylosin based on the evaluation of MG infection and tylosin treatment on the lung microbiota.

Transcriptomic Analysis of Long-Term Protective Immunity Induced by Vaccination With Mycoplasma gallisepticum Strain ts-304

Live attenuated vaccines are commonly used to control Mycoplasma gallisepticum infections in chickens. M. gallisepticum ts-304 is a novel live attenuated vaccine strain that has been shown to be safe and effective. In this study, the transcriptional profiles of genes in the tracheal mucosa in chickens challenged with the M. gallisepticum wild-type strain Ap3AS at 57 weeks after vaccination with ts-304 were explored and compared with the profiles of unvaccinated chickens that had been challenged with strain Ap3AS, unvaccinated and unchallenged chickens, and vaccinated but unchallenged chickens. At two weeks after challenge, pair-wise comparisons of transcription in vaccinated-only, vaccinated-and-challenged and unvaccinated and unchallenged birds detected no differences. However, the challenged-only birds had significant up-regulation in the transcription of genes and enrichment of gene ontologies, pathways and protein classes involved in infiltration and proliferation of inflammatory cells and immune responses mediated through enhanced cytokine and chemokine production and signaling, while those predicted to be involved in formation and motor movement of cilia and formation of the cellular cytoskeleton were significantly down-regulated. The transcriptional changes associated with the inflammatory response were less severe in these mature birds than in the relatively young birds examined in a previous study. The findings of this study demonstrated that vaccination with the attenuated M. gallisepticum strain ts-304 protects against the transcriptional changes associated with the inflammatory response and pathological changes in the tracheal mucosa caused by infection with M. gallisepticum in chickens for at least 57 weeks after vaccination.

Minimal inhibitory concentration of seven antimicrobials to Mycoplasma gallisepticum and Mycoplasma synoviae isolates from six European countries

Mycoplasma gallisepticum and Mycoplasma synoviae are bacterial pathogens that cause disease in poultry, adversely affecting their health and welfare, and are a financial burden on producers. This manuscript describes the results of the MycoPath project that is the first international antimicrobial susceptibility programme for mycoplasma pathogens isolated from poultry. Improved comparative analysis of minimal inhibitory concentration (MIC) results from participating countries was facilitated by using one laboratory determining all MICs. Chicken and turkey isolates were obtained from France, Germany, Great Britain, Hungary, Italy and Spain during 2014-2016. One isolate per farm was retained. The MIC of seven antimicrobial agents was determined using a broth microdilution method, with Friis Medium (M. gallisepticum) or Modified Chanock's Medium (M. synoviae). Of the 222 isolates recovered, 82 were M. gallisepticum and 130 were M. synoviae. M. gallisepticum MIC_50/90 values were 0.12/0.5, 2/8, 0.5/4, 0.12/>64, 0.008/0.062, 0.008/32, 0.062/4 mg/l for doxycycline, enrofloxacin, oxytetracycline, spiramycin, tiamulin, tilmicosin and tylosin, respectively. For M. synoviae, the values were 0.5/1, 8/16, 0.5/1, 0.5/8, 0.25/0.5, 0.062/2 and 0.062/16 mg/l respectively. A bimodal MIC distribution for the fluoroquinolone (enrofloxacin) and the macrolides (spiramycin, tilmicosin and tylosin) indicate that both species have sub-populations that are less susceptible in vitro to those antimicrobials. Some differences in susceptibilities were observed according to host species, Mycoplasma species, and country of origin. This study provides a baseline of novel data for future monitoring of antimicrobial resistance in poultry Mycoplasma species. Additionally, this information will facilitate the selection of the antimicrobial agents most likely to be effective, thus ensuring their minimal use with targeted and correct therapeutic treatments.Highlights First large-scale pan-European collection of representative Mg and Ms isolates.MIC values assessed in central laboratory for Mg and Ms from chickens and turkeys.Range of MIC values for 82 Mg and 130 Ms isolates to seven licenced antibiotics shown.Data can be used to help determine Mg and Ms veterinary-specific breakpoints.

Decrease of Mycoplasma gallisepticum seroprevalence and introduction of new genotypes in Dutch commercial poultry during the years 2001-2018

Almost two decades ago, in addition to a compulsory M. gallisepticum (Mg) monitoring programme of breeding stock based on European Union regulations, the Dutch poultry industry added national regulations to further reduce the Mg prevalence in Dutch commercial poultry. Currently, all commercial chicken and turkey flocks except broilers are monitored for Mg. All breeding flocks on a farm where one or more flocks tested Mg positive are culled. Mg positive layer pullets are channelled and layer pullets placed on Mg positive multi-age farms are vaccinated. The monitoring data obtained were analysed covering a period of 17 years. Moreover, 31 Dutch Mg isolates from the same period were analysed by multilocus sequence typing (MLST) and compared to available PubMLST data. The results show that in breeding stock the seroprevalence decreased from 1.6% to 0.0%, in commercial layers from 6.3% to 1.9%, and in meat turkeys from 17.6% to 2.4%. The MLST results showed the presence of closely related and identical sequence types (STs) within the different Dutch poultry types. Similar STs were found in Northern and Southern Europe only. The results show a fast decline in the Mg prevalence since 2001, although in layers the Mg prevalence has stabilized and suggests backyard poultry might pose a risk for commercial poultry. The need for Mg control across poultry sectors and in trade was confirmed by the similarity in STs found in different types of poultry and regions. These results from the Dutch poultry industry can be extrapolated to Mg control in general.

A Herpesvirus of Turkey-Based Vector Vaccine Reduces Transmission of Newcastle Disease Virus in Commercial Broiler Chickens with Maternally Derived Antibodies

Newcastle Disease is one of the most important infectious poultry diseases worldwide and is associated with high morbidity, mortality, and economic loss. In several countries, vaccination is applied to prevent and control outbreaks; however, information on the ability of vaccines to reduce transmission of ND virus (NDV) is sparse. Here we quantified the transmission of velogenic NDV among 42-day-old broilers. Chickens were either vaccinated with a single dose of a vector vaccine expressing the F protein (rHVT-ND) at day-old in the presence of maternally derived antibodies or kept unvaccinated. Seeders were challenged 8 h before the co-mingling with the corresponding contacts from the same group. Infection was monitored by daily testing of cloacal and oro-nasal swabs with reverse transcription-real-time PCR and by serology. Vaccinated birds were completely protected against clinical disease and virus excretion was significantly reduced compared to the unvaccinated controls that all died during the experiment. The reproduction ratio, which is the average number of secondary infections caused by an infectious bird, was significantly lower in the vaccinated group (0.82 (95% CI 0.38-1.75)) than in the unvaccinated group (3.2 (95% CI 2.06-4.96)). Results of this study demonstrate the potential of rHVT-ND vaccine in prevention and control of ND outbreaks.

Antimicrobial Resistance in Mycoplasma spp

Mycoplasmas are intrinsically resistant to antimicrobials targeting the cell wall (fosfomycin, glycopeptides, or β-lactam antibiotics) and to sulfonamides, first-generation quinolones, trimethoprim, polymixins, and rifampicin. The antibiotics most frequently used to control mycoplasmal infections in animals are macrolides and tetracyclines. Lincosamides, fluoroquinolones, pleuromutilins, phenicols, and aminoglycosides can also be active. Standardization of methods used for determination of susceptibility levels is difficult since no quality control strains are available and because of species-specific growth requirements. Reduced susceptibility levels or resistances to several families of antimicrobials have been reported in field isolates of pathogenic Mycoplasma species of major veterinary interest: M. gallisepticum and M. synoviae in poultry; M. hyopneumoniae, M. hyorhinis, and M. hyosynoviae in swine; M. bovis in cattle; and M. agalactiae in small ruminants. The highest resistances are observed for macrolides, followed by tetracyclines. Most strains remain susceptible to fluoroquinolones. Pleuromutilins are the most effective antibiotics in vitro. Resistance frequencies vary according to the Mycoplasma species but also according to the countries or groups of animals from which the samples were taken. Point mutations in the target genes of different antimicrobials have been identified in resistant field isolates, in vitro-selected mutants, or strains reisolated after an experimental infection followed by one or several treatments: DNA-gyrase and topoisomerase IV for fluoroquinolones; 23S rRNA for macrolides, lincosamides, pleuromutilins, and amphenicols; 16S rRNAs for tetracyclines and aminoglycosides. Further work should be carried out to determine and harmonize specific breakpoints for animal mycoplasmas so that in vitro information can be used to provide advice on selection of in vivo treatments.

Egg quality in laying hens exposed to Mycoplasma gallisepticum F-strain attenuated vaccine

Mycoplasma gallisepticum causes coughing, ocular and nasal discharge, reduction in feed intake, lower and uneven growth, decline in egg production and quality, and increase in mortality. Among the attenuated vaccination strains, MGF can reduce clinical signs and lesions in layer hens, stimulate immune responses of cellular and humoral basis, act as an instrument of competitive exclusion in relation to field strains, and reduce the use of antimicrobials. This study aimed to investigate the effects of attenuated MG F-strain vaccination on egg quality in 3 groups of 30 hens each, being one control and 2 vaccinated. Vaccination was applied by ocular route at 8 and 12 wk of age. Comparisons were made among unvaccinated hens; vaccinated at 8 wk of age; and vaccinated at 8 and 12 wk of age. There were no statistical differences in eggshell thickness and weight among groups. Eggs from twice vaccinated birds yielded a Haugh unit significantly lower than the other groups without affecting egg classification. There was no significant difference in ELISA results between the vaccinated groups.

Quantification of the horizontal transmission of Mycoplasma synoviae in non-vaccinated and MS-H-vaccinated layers

The number of newly infected birds attributable to one infectious bird per day (= transmission rate β) was assessed in non-vaccinated and MS-H-vaccinated experimental specified pathogen-free White Leghorns after Mycoplasma synoviae challenge. Furthermore, the effect of vaccination on the shedding of the challenge strain was determined. The following groups were made: a negative control group (n = 5), a vaccinated (MS-H vaccine by eye drop (>10^5.7 colour changing units/bird)) non-challenged group (n = 5), two non-vaccinated challenged groups (n = 18 each) and two vaccinated challenged groups (n = 18 each). In the challenged groups, six seeder birds were intratracheally inoculated with 10^5.4 colony forming units (CFUs)/bird. Trachea swabs were taken at day (D)2, D3, D4, D5, D7, D9, D11, D14, D17, D21, D25, D28, D32, D35, D42 and D46 after contact with seeders and analyzed with a quantitative PCR able to detect the vaccine and field strain separately. The transmission rate and shedding were estimated using the susceptible exposed infectious transmission model and a linear mixed model, respectively. The mean shedding of the challenge strain was 10^6.4 CFU equivalents M. synoviae/g trachea mucus in vaccinates shedding MS-H, while in the birds not shedding the vaccine (non-vaccinates and vaccinates not shedding MS-H) it was 10^6.9 CFU equivalents M. synoviae/g trachea mucus. In vaccinates shedding MS-H, β was 0.0012 (95% C.I.: 0.00048 - 0.0024), while in birds not shedding vaccine (non-vaccinates and vaccinates not shedding MS-H) a significantly higher β of 0.022 (95% C.I.: 0.015 - 0.031) was found.

Seroprevalence of Mycoplasma synoviae in Dutch commercial poultry farms

Before the year 2000, Mycoplasma synoviae was associated mainly with subclinical respiratory infections in broilers in the Netherlands and was considered to have low clinical and economic impact. The subsequent occurrence of M. synoviae arthritis and amyloid arthropathy, and of eggshell apex abnormalities, has resulted in an increasing demand for M. synoviae-free poultry. Therefore, a cross-sectional seroprevalence study was carried out over a 12-month period during 2005 and 2006. Ten blood samples per farm were generally used because M. synoviae was expected to spread quickly. However, for grandparent and layer breeder stock, 24 to 60 blood samples per house were available from a voluntary M. synoviae monitoring programme. Sera were tested by means of the rapid plate agglutination test (agglutination at dilution > or =1:8 was considered positive). The numbers of farms sampled out of the national total were: broiler grandparent, 53/53; broiler parent rearing, 34/150; broiler parent, 114/300; broiler, 185/800; layer grandparent, 13/13; layer parent, 40/50; layer, 173/1250; and meat turkey, 50/75. The seroprevalence of M. synoviae in commercial poultry was high, especially in commercial layers where it was 73% (95% confidence interval (CI)=67 to 80); in layer and broiler grandparent stock, the seroprevalence was 0% and 10%, respectively, based on sample sizes equal to the population size. In layer and broiler parent farms, the seroprevalence was 25% (95% CI=19 to 31) and 35% (95% CI=28 to 44); in both broiler parent rearing and broiler farms it was 6% (95% CI=0 to 13 and 95% CI=3 to 9); and in meat turkey, the seroprevalence was 16% (95% CI=10 to 22).

Vaccines for Mycoplasma diseases in animals and man

Vaccines for important mycoplasma diseases, including contagious bovine and caprine pleuropneumonia, have been used for centuries, consisting mainly of infected tissue or fluids which are inoculated into sites at which the risk of severe infection is slight, such as the tail and bridge of the nose. Surprisingly, little progress has been made in developing safe, defined and protective alternatives, the vaccines today still consisting of mildly attenuated strains serially passaged in eggs or in culture. Ill-defined temperature-sensitive mutants are widely used for mycoplasmoses in poultry despite uncertainty about their mode of protection. Inactivated vaccines for enzootic pneumonia appear to have improved pig health worldwide, but disease reduction has been generally modest. Ironically, attempts to develop subunit preparations have often led to exacerbation of disease, particularly in human atypical pneumonia. Promising results have been seen in DNA vaccine technology, which has been applied to the development of mycoplasma vaccines for porcine enzootic pneumonia, but field trials still seem a long way off. No commercial vaccines exist for Mycoplasma bovis, despite evidence that this is a major cause of calf pneumonia, mastitis and arthritis.

Differentiation of Mycoplasma gallisepticum vaccine strains ts-11 and 6/85 from commonly used Mycoplasma gallisepticum challenge strains by PCR

Mycoplasma gallisepticum (MG) is an important avian pathogen causing significant economic losses within the poultry industry. In an effort to develop tools to aid in MG research and diagnostics, we have compared sequences of the attenuated MG vaccine strain ts-11 to those of commonly used pathogenic challenge strains in search of a simple means of differentiation. Via gapA sequence alignments and comparisons, we have identified and designed primers facilitating strain differentiation. When applied to conventional polymerase chain reaction (PCR) assay at low annealing temperature, the primer sets allow for the differentiation of MG attenuated vaccine strains ts-11 as well as the attenuated MG vaccine strain 6/85 from the commonly utilized MG challenge strains R(low), R, and S6. Conventional PCR differentiation is based on the visualization of sole products with the attenuated MG strains ts-11 and 6/85 and the lack of the corresponding products from MG strains R(low), R, and S6. When applied to MG strain F, product visualization varies with the applied primer set. The differentiation of MG strains ts-11 and 6/85 from the pathogenic challenge strains was also accomplished via real-time analyses, however, the primer sets were not able to differentiate MG strains ts-11 and 6/85 from selected MG field isolates.