Effect of infection route and concurrent infectious bronchitis virus vaccination onMycoplasma gallisepticumdisease pathology in an experimental model

Effect of co-infection with Newcastle disease virus on Mycoplasma gallisepticum pathogenesis in vivo and in vitro

The co-infection of Newcastle disease virus (NDV) and Mycoplasma gallisepticum (MG) has a detrimental effect on chicken production performance, exerts a deleterious impact on poultry production performance, resulting in substantial economic losses. However, the exact impact and underlying mechanisms remain ambiguous. In this study, co-infection models were established both in vivo and in vitro. Through these models, it was found that the co-infection facilitated the replication of MG and NDV, as well as MG induced pathogenesis. The administration of lentogenic NDV resulted in the suppression of the innate immune response in vivo. At cellular level, co-infection promoted MG induced apoptosis through caspase-dependent mitochondrial endogenous pathway and suppressed the inflammatory secretion. This research contributes novel insights in co-infection.

Development and Evaluation of Mycoplasma gallisepticum Challenge Model in Layer Pullets

Manufacturers of Mycoplasma gallisepticum (MG) modified live vaccines usually recommend a single application at 8 wk of age. This makes 12-16-wk-old layer pullets suitable for challenge studies intended to evaluate these vaccines. Numerous challenge models in different poultry species and ages have been reported. However, there is not an established layer pullet challenge model for this age. The aim of this study is to develop a suitable challenge model in 12-wk-old layer pullets. MG Rlow strain was used as the challenge strain, and its ability to induce clinical signs and lesions in 12-wk-old Hy-Line W-36 layer pullets was evaluated. Three different doses (low, 7.95 × 104 color-changing units [CCU]/bird; medium, 7.95 × 106 CCU/bird; and high, 7.95 × 108 CCU/bird) via three different routes (eye drop, fine spray, and contact infection) were compared and evaluated using different parameters. At 14 days post-challenge, there were no mortalities in any of the groups throughout the study. Layer pullets directly challenged with the high dose via the fine spray route showed the clearest and most consistent results (clinical signs, positive quantitative real-time PCR [qPCR], seroconversion, air sac scoring, and histopathological changes of the tracheal mucosa). Medium and low challenge doses applied via fine spray or eye drop did not show consistent results. Rlow strain was able to spread to the contact infection birds, as confirmed by the positive qPCR results; however, none of the contact-infected birds showed any clinical signs or gross or microscopic lesions. Our results suggest that a high dose (7.95 × 108 CCU/bird) administered through a fine spray route is the model of choice in any future MG vaccine evaluation trials in 12-wk-old layer pullets.

Molecular detection of respiratory avian mycoplasmosis associated bacterial and viral concurrent infections in the poultry flocks

Respiratory tract infections are of serious concern to the poultry industry. The present study was aimed to delineate the extent of respiratory avian mycoplasmosis associated bacterial and viral concurrent infections in the poultry flocks. A total of 146 poultry flocks of Haryana and Rajasthan, India, suspected for chronic respiratory disease (CRD) were screened for avian mycoplasmas, Newcastle disease virus (NDV), infectious bronchitis virus (IBV), and avian pathogenic Escherichia coli (APEC) by conventional polymerase chain reaction (PCR) assays. A total of 49.31% (72/146) flocks were found positive for Mycoplasma infection. Of the Mycoplasma-positive flocks, 80.55% (58/72) represented pathogenic avian mycoplasmas (MG and/or MS), while 19.44% (14/72) flocks were positive for commensal avian mycoplasmas (other than MG and MS). A correlation was deduced between avian mycoplasmosis and bacterial and/or viral co-infections. The results revealed that 17.24% (10/58) flocks had only avian mycoplasmosis infection. However, in the remaining flocks, the avian mycoplasmosis was associated either with APEC infection [17.24% (10/58)], IBV infection [43.10% (25/58)], or both APEC and IBV infections [22.41% (13/58)], respectively. Further epidemiological studies on respiratory avian mycoplasmosis associated concurrent infections with other pathogens are recommended to assess circulating strains, risk factors, and economic losses.

The impact of the experimental route of challenge on the host responses and pathogenesis of the Canadian Delmarva (DMV/1639) infectious bronchitis virus infection in laying chickens

Infectious bronchitis virus (IBV) infection can be associated with respiratory, renal, and/or reproductive diseases in chickens. Under natural conditions, conjunctiva, mucosa of upper respiratory tract, and cloaca are the main routes of IBV entry. Experimentally, the study of IBV infection involved various routes of inoculation. This study investigated the impact of adding the trachea as a potential route of viral entry to the oculo-nasal infection on the host responses, pathogenicity, and tissue tropism of the Canadian IBV Delmarva (DMV/1639) strain in laying chickens. Specific-pathogen-free laying chickens were divided into three experimental groups: control group (Con group), oculo-nasal challenged group (ON group), and oculo-nasal/intratracheal challenged group (ON/IT group); all groups were observed for 12 days post-infection (dpi). The clinical signs and reduction in egg production in the ON/IT group started slightly earlier compared to the ON group. At 12 dpi, the gross lesions in the ON/IT group were confined to the ovary, while the ON group showed regressed ovary and atrophied oviduct. Only the ON group showed significantly higher microscopic lesion scores in the lung, kidney, magnum, and uterus compared to the control group at 12 dpi. The oviduct tissues of the ON group showed a significant increase in B cells infiltration compared to ON/IT and control groups. The viral shedding (detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR)), tissue tropism (detected either by qRT-PCR or immunohistochemistry (IHC)), T/natural killer cells infiltration in reproductive tract (detected by IHC), and antibody-mediated immune responses (measured by enzyme-linked immunosorbent assay) showed similar patterns in the ON and ON/IT groups.

Andrographolide restored production performances and serum biochemical indexes and attenuated organs damage in Mycoplasma gallisepticum-infected broilers

1. This study aimed to study the preventive and therapeutic effects of andrographolide (Andro) during Mycoplasma gallisepticum HS strain (MG) infection in ArborAcres (AA) broilers.2. The minimum inhibitory concentration (MIC) of Andro against MG was measured. Broiler body weight, feed efficiency, morbidity, cure rate and mortality were recorded during the experiment. Air sac lesion scores and immune organ index were calculated. Expression of pMGA1.2 in lung tissue and serum biochemical indices were examined. Histopathological examinations of immune organs, liver, trachea and lung tissue were conducted by Haematoxylin and Eosin stain.3. MIC was 3.75 μg/mL and Andro significantly inhibited the expression of pMGA1.2 (P ≤ 0.05). Compared with control MG-infected group, Andro low-dose and high-dose prevention reduced the morbidity of chronic respiratory disease in 40.00% and 50.00%, respectively. Mortality of C, D and E group was 16.67%, 10.00% and 6.67%, respectively. Cure rate of E, F, G and H group was 92.00%, 92.86%, 93.33% and 100.0%, respectively. Compared with control MG-infected group, Andro treatment significantly increased average weight gain (AWG), relative weight gain rate (RWG) and feed conversion rate (FCR) at 18 to 24 days (P ≤ 0.05). Compared with control group, Andro alone treatment significantly increased AWG in broilers (P ≤ 0.05).4. Compared with control MG-infected group, Andro significantly attenuated MG-induced air sac lesion, immune organs, liver, trachea and lung damage in broilers. Andro alone treatment did not induce abnormal morphological changes in these organs in healthy broilers. Serum biochemical analysis results showed, comparing with control MG-infected group, Andro significantly decreased the content of total protein, albumin, globulin, alanine aminotransferase, aspartate aminotransferase, total bilirubin, urea, creatinine, uric acid, total cholesterol, and increased the albumin/globulin ratio and content of alkaline phosphatase, apolipoprotein B and apolipoprotein A-I in a dose-dependent manner (P ≤ 0.05).5. Andro could act as a potential agent against MG infection in broilers.

Measures of tracheal lesions are more discriminatory and reproducible indications of chronic respiratory disease caused by Mycoplasma gallisepticum in poultry

Mycoplasma gallisepticum is the primary causative agent of chronic respiratory disease in poultry and vaccination is the measure most commonly used for its control. Pathological changes caused by M. gallisepticum are mainly observed in the trachea and air sacs, but assessment of air sac lesions is subjective. Standardised parameters for evaluation of pathological changes, and their reproducibility and discrimination in uninfected and infected groups, are critical when assessing the efficacy of M. gallisepticum vaccination. This study reviewed and critically appraised the published literature on evaluation of vaccine efficacy against pathological changes caused by M. gallisepticum in poultry in the trachea and air sacs. A search of four electronic databases, with subsequent manual filtering, identified 23 eligible papers published since 1962 describing the assessment of histopathological changes in the trachea using tracheal lesion scores and/or measurement of tracheal mucosal thicknesses and assessment of gross air sac lesions using lesion scores. Measurement of tracheal lesions proved a more reliable and robust method of assessing disease induced by M. gallisepticum when compared to assessment of air sac lesions, highlighting the importance of including assessment of tracheal lesions as the primary outcome variable in vaccine efficacy studies. In addition, this study also identified the necessity for use of a standardised model for evaluation and reporting on M. gallisepticum vaccines to minimise variations between vaccine efficacy studies and to allow direct comparisons between them.

Evaluation of Glycyrrhizic Acid Therapeutic Effect and Safety in Mycoplasma gallisepticum (HS Strain)-Infected Arbor Acres Broilers

This study was conducted to evaluate the therapeutic effects and safety of GA in MG-infected broilers. Our results showed that the minimum inhibitory concentration of GA was 31.25 μg/mL. Moreover, GA inhibited the expression of MG adhesion protein (pMGA1.2) in the broilers' lungs. GA treatment clearly decreased the morbidity of CRD and mortality in the MG-infected broilers. Compared with the model group, GA treatment significantly decreased gross air sac lesion scores and increased average weight gain and feed conversion rate in the MG-infected broilers. Histopathological examination showed GA treatment attenuated MG-induced trachea, immune organ and liver damage in the broilers. Moreover, GA treatment alone did not induce abnormal morphological changes in these organs in the healthy broilers. Compared with the model group, serum biochemical results showed GA treatment significantly decreased the content of total protein, albumin, globulin, alanine aminotransferase, aspartate aminotransferase, total bilirubin, creatinine, uric acid, total cholesterol, and increased the content of albumin/globulin, alkaline phosphatase, apolipoprotein B and apolipoprotein A-I. In conclusion, GA displayed a significant therapeutic efficacy regarding MG infection and had no adverse effects on the broilers (100 mg/kg/d).

Clinical expression, epidemiology and monitoring of Mycoplasma gallisepticum and Mycoplasma synoviae: an update

Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) are of clinical and economic importance for the global poultry industry. Many countries and integrations are involved in monitoring programs to control both mycoplasma species. This review provides an extensive historic overview of the last seven decades on the development of the knowledge regarding the factors that influence the clinical expression of the disease, the epidemiology and monitoring of both MG and MS. This includes the detection of new virulent strains, studies unravelling the transmission routes, survival characteristics and the role of other avian hosts. Also the role of molecular typing tests in unravelling epidemiology, and factors that complicate the interpretation of test results such as heterologous mycoplasma infections, use of heterologous oil-emulsion vaccines, use of antibiotic treatments, occurrence of MG and MS strains with low virulence, and last but not least the use of live and/or inactivated MG and MS vaccines are discussed.

Fluorescent microspheres as a positive indicator in an intratracheal infection model

Animal models testing the ability of vaccines and therapeutic agents to prevent pathology from induced respiratory infection are an important means of testing and validating the vaccines and therapeutic agents. However, the lack of induced pathology in test subjects could be either indicative of protection or a problem with the animal model system. This work describes the improvement of a chicken model system of intratracheal infection using fluorescent microspheres as a positive indicator of infection. It was shown that fluorescent microspheres and Mycoplasma gallisepticum bacteria both dispersed to the same areas of the chicken respiratory system and that the microspheres remained detectable in the chicken lung tissue for at least 7 days following infection. The microspheres used are detectable using a black light, allowing for visualization during necropsy. Using the updated model system, three live M. gallisepticum vaccines were tested both for their ability to elicit a humoral immune response following vaccination, and for their ability to protect from air sac lesion pathology at two different time points following vaccination. Results showed the protective effects of the different M. gallisepticum vaccines prevented the induction of pathology, consistent with previous results. The presence of the fluorescent microspheres provided a positive method of identifying the properly infected chickens and a means of differentiating failed experimental infections so that those samples could be removed, resulting in improved consistency in infection results.

Comparison of Experimental Infection of Normal and Immunosuppressed Chickens with Mycoplasma gallisepticum

Four different models of infection of chickens with Mycoplasma gallisepticum (MG) were evaluated. Normal or immunosuppressed chicks (10 days old) were infected with the MG R_low strain via eye and nasal drops or by direct air sac injection. Bacterial load in the lungs was quantified and air sac and tracheal lesion scores, tracheal mucosal thickness and humoral immune responses were assessed. Serum antibody responses were assessed by use of a serum plate agglutination test. Three days post infection (dpi), all immunosuppressed chicks had developed significant respiratory signs. Chicks infected via air sac injection had significant differences in serum antibody and gross lesion scores at 5 dpi. All chicks had developed pathological changes by 7 dpi. Air sac inoculation of immunosuppressed chicks produced more significant (P ≤0.05) lesions, and these birds had the highest bacterial load in the lungs compared with other groups.

Baicalin Attenuates Mycoplasma gallisepticum-Induced Inflammation via Inhibition of the TLR2-NF-κB Pathway in Chicken and DF-1 Cells

Background

Previous reports demonstrated that baicalin possesses potential anti-inflammatory properties. The present study was conducted to determine the effects of baicalin against inflammatory responses in chicken and DF-1 cells infected with Mycoplasma gallisepticum (MG).

Methods

An MG infection model was developed in chickens to study the anti-inflammatory mechanism of baicalin. Baicalin was mixed in water at a dose of 450 mg/kg per day, and the treatment is continued for 7 consecutive days. Samples were taken at 1, 4, and 7 days post treatment.

Results

By using transmission electron microscopy, ultrastructure of lung and tracheal cells has been examined. It can be seen that the cilia cells in the MG-infected group have pyknosis, degeneration, and necrosis. In the lung tissues, alveolar type-I epithelial cells were severely damaged. In the baicalin-treated group, cilia were swollen, mushroom-shaped edema bubbles formed on the apex, and fused together. Alveolar type I epithelial cells injury was significantly reduced. Compared to MG-infection group, the levels of proinflammatory cytokines IL-1β and TNF-α were significantly decreased (P < 0.01). The corresponding proteins TLR2 and P-p65 decreased in the baicalin-treated group after 1 (p > 0.05), 4 (p < 0.05), and 7 days (p < 0.05), respectively.

Conclusion

The results showed that baicalin can interfere with inflammatory injury by suppressing the release of inflammatory cytokines IL-1β and TNF-α during MG infection both in vivo and in vitro. Meanwhile, baicalin suppressed TLR2-NFκB signaling pathway by inhibiting the phosphorylation of p65 and IκB, thereby affecting the expression of inflammatory factors. The results suggested that baicalin acts as a potential anti-inflammatory agent against MG infection in chicken and DF-1 cells.

Cathepsin L promotes secretory IgA response by participating in antigen presentation pathways during Mycoplasma Hyopneumoniae infection

Cathepsin L (CTSL) has been proved to help contain leishmaniasis and mycoplasma infection in mice by supporting cellular immune responses, but the regulatory functions of CTSL on mucosal immune responses haven't been tested and remain undefined. Here, we investigated the effects of CTSL on SIgA responses and invariant chain (Ii) degradations in the co-cultured swine dendritic cells (DCs) and B cells system in vitro. When the cells system were transfected with vector CTSL-GFP or incubated with recombinant CTSL (rCTSL) before they were infected with Mycoplasma hyopneumoniae (M.hp), SIgA significantly increased and Ii chain was degraded into smaller intermediates, while SIgA decreased when CTSL was knockdown or inhibited with E64. To confirm the SIgA responses promoted by CTSL contribute to the resistance to mycoplasma pneumonia, pigs injected with rCTSL before they were challenged with M.hp, showed milder clinical symptoms and histopathological damage of lungs, less mycoplasma burden together with higher secretion of SIgA, percentages of CD4+ T cells and level of MHC II molecules comparing with the group without rCTSL. Collectively, these results suggested that rCTSL could provide effective protection for piglets against mycoplasma pneumonia by enhancing M.hp-specific mucosal immune responses through its role in antigen presentation by processing the invariant chain.

Assessment of Mycoplasma gallisepticum vaccine efficacy in a co-infection challenge model with QX-like infectious bronchitis virus

Mycoplasma gallisepticum (MG) is the primary cause of chronic respiratory disease in poultry. We investigated the protective efficacy of the live-attenuated ts-11 and 6/85 MG vaccines against a local MG strain and, in order to enhance signs and mimic a typical field situation, we co-infected birds with a virulent strain of QX-like infectious bronchitis virus (IBV). Both vaccines showed similar ability to protect infected chickens from clinical signs, although ts-11 performed slightly better. Despite the lower protection against clinical disease, 6/85-vaccinated birds had significantly (P ≤ 0.05) lower tracheal lesion scores and mucosal thickness at day 28 post-vaccination (7 days post-challenge [dpc] with MG, 2 dpc IBV) and day 31 post-vaccination (10 dpc MG challenge, 5 dpc IBV) compared to ts-11 vaccinated birds, but these difference was not significant at day 33 (12 dpc MG, 7 dpc IBV). Pathogen infection and replication was assessed by qPCR, and the 6/85 vaccine produced a more significant (P ≤ 0.05) reduction in MG replication in the lungs, kidneys and livers but enhanced late replication in bursae and caecal tonsils. In contrast, the ts-11 vaccine had a more pronounced reductive effect on replication in tracheas, air sacs, bursae and heart at days 28 and 31, yet increased replication in lungs. Interestingly, both vaccines provided non-specific protection against IBV challenge. The co-challenge model provided useful data on vaccine efficacy, especially on days 31 and 33, and tracheas, lungs, air sacs, kidneys, liver and caecal tonsils were the best organs to assess.

Mycoplasma gallisepticum modifies the pathogenesis of influenza A virus in the avian tracheal epithelium

Multiple respiratory infections have a significant impact on health and economy. Pathogenesis of co-infecting viruses and bacteria and their interaction with mucosal surfaces are poorly characterized. In this study we established a co-infection model based on pre-incubation of tracheal organ cultures (TOC) with Mycoplasma (M.) gallisepticum and a subsequent infection with avian influenza virus (AIV). Mycoplasma gallisepticum modified the pathogenesis of AIV as demonstrated in TOC of two different avian species (chickens and turkeys). Co-infection promoted bacterial growth in tracheal epithelium. Depending on the interaction time of M. gallisepticum with the host cells, AIV replication was either promoted or suppressed. M. gallisepticum inhibited the antiviral gene expression and affected AIV attachment to the host cell by desialylation of α-2,3 linked sialic acids. Ultrastructural analysis of co-infected TOC suggests that both pathogens may attach to and possibly infect the same epithelial cell. The obtained results contribute to better understanding of the interaction dynamics between M. gallisepticum and AIV. They highlight the importance of the time interval between infections as well as the biological properties of the involved pathogens as influencing factors in the outcome of respiratory infections.

Co-infection with Multiple Respiratory Pathogens Contributes to Increased Mortality Rates in Algerian Poultry Flocks

Respiratory infections are a common cause for increased mortality rates in poultry worldwide. To improve intervention strategies, circulating pathogens have to be identified and further characterized. Because of the lack of diagnostic tools, it was not known what pathogens contribute to the high mortality rates in association with respiratory disease in Algeria. Our objective was to determine if primary pathogens including Mycoplasma gallisepticum (MG), Mycoplasma synoviae (MS), avian influenza virus (AIV), infectious bronchitis virus (IBV), and avian metapneumovirus (aMPV), known to be present in neighboring countries, can also be detected in Algerian chicken and turkey flocks. Results demonstrate the circulation of the investigated pathogens in Algerian poultry flocks as multi-infections. Phylogenetic characterization of the Algerian IBV strains confirmed the circulation of nephropathogenic viruses that are different from the strains isolated in neighboring countries. This could suggest the existence of a new IBV genotype in North Africa. Additionally, we detected for the first time an aMPV subtype B field strain and avian influenza virus. Interestingly, all viral pathogens were present in co-infections with MG, which could exacerbate clinical disease. Additional pathogens may be present and should be investigated in the future. Our results suggest that multiple respiratory infections may be responsible for high mortality in Algerian poultry flocks and very probably also in other regions of the world, which demonstrates the need for the establishment of more comprehensive control strategies.