Effects of age, environmental temperature and relative humidity on the colonization of the nose and trachea of calves by Mycoplasma spp

Utilizing the Gastrointestinal Microbiota to Modulate Cattle Health through the Microbiome-Gut-Organ Axes

The microorganisms inhabiting the gastrointestinal tract (GIT) of ruminants have a mutualistic relationship with the host that influences the efficiency and health of the ruminants. The GIT microbiota interacts with the host immune system to influence not only the GIT, but other organs in the body as well. The objective of this review is to highlight the importance of the role the gastrointestinal microbiota plays in modulating the health of a host through communication with different organs in the body through the microbiome-gut-organ axes. Among other things, the GIT microbiota produces metabolites for the host and prevents the colonization of pathogens. In order to prevent dysbiosis of the GIT microbiota, gut microbial therapies can be utilized to re-introduce beneficial bacteria and regain homeostasis within the rumen environment and promote gastrointestinal health. Additionally, controlling GIT dysbiosis can aid the immune system in preventing disfunction in other organ systems in the body through the microbiome-gut-brain axis, the microbiome-gut-lung axis, the microbiome-gut-mammary axis, and the microbiome-gut-reproductive axis.

Contribution of the Mucosal Microbiota to Bovine Respiratory Health

Recognizing the respiratory tract as a dynamic and complex ecosystem has enhanced our understanding of the pathophysiology of bovine respiratory disease (BRD). There is widespread evidence showing that disease-predisposing factors often disrupt the respiratory microbial ecosystem, provoking atypical colonization patterns and a progressive dysbiosis. The ecological factors that shape the respiratory microbiota, and the influence of these complex communities on bovine respiratory health, are a rich area for research exploration. Here, we review the current status of understanding of the bovine respiratory microbiota, the factors that influence its development and stability, its role in maintaining mucosal homeostasis, and ultimately its contribution to bovine health and disease. Finally, we explore the limitations of current research approaches to the microbiome and discuss potential directions for future research that can help us better understand the role of the respiratory microbiota in the health, welfare, and productivity of livestock.

Interactive effects of dexamethasone and opsonized Mycoplasma bovis on bovine neutrophil function in vitro

Previously we had reported that exposure to high levels of glucocorticoids, and to unopsonized Mycoplasma bovis, has a negative interactive effect on bovine neutrophil function in vitro, and this interactive effect was a function of M. bovis strain differences. Here we hypothesized that in vitro treatment of bovine neutrophils by glucocorticoid would impair phagocytosis of opsonized M. bovis compared to non-treated neutrophils and such impairment would be a function of M. bovis strain differences. Neutrophils isolated from 20 mid-lactation cows were treated with immunosuppressive dose of 5 × 10^-4 M dexamethasone or placebo and incubated with one of four opsonized M. bovis strains that had been isolated from bovine origin. After incubation neutrophil function measured included: percentage reduction in log₁₀ of M. bovis CFU/ml, percentage of phagocytizing neutrophils, phagocytized M. bovis per neutrophil, and killed M. bovis per neutrophil. Least square means of all neutrophil groups were contrasted using linear mixed-effects models. Effects due to strain, treatment, and their interaction on neutrophil function measured by the number of phagocytized M. bovis per neutrophil and number of killed M. bovis per neutrophil were different (P < 0.05). However, no significant strain by treatment interaction effect on percentage reduction in log₁₀ of M. bovis CFU/ml was found. Neither a strain nor a strain by treatment interaction was found to affect the percentage phagocytizing neutrophils. These findings might explain in part the association of stressful events with subsequent outbreaks of Mycoplasma bovis associated bovine diseases.

Gap analysis of Mycoplasma bovis disease, diagnosis and control: An aid to identify future development requirements

There is a worldwide problem of disease caused by Mycoplasma (M.) bovis in cattle; it has a significant detrimental economic and animal welfare impact on cattle rearing. Infection can manifest as a plethora of clinical signs including mastitis, pneumonia, arthritis, keratoconjunctivitis, otitis media and genital disorders that may result in infertility and abortion. Current diagnosis and control information are reviewed and analysed to identify gaps in knowledge of the causative organism in respect of the disease pathology, diagnosis and control methods. The main considerations are as follows: no vaccines are commercially available; antimicrobial resistance is increasing; diagnostic and antimicrobial sensitivity testing needs to be improved; and a pen-side test would facilitate more rapid diagnosis and implementation of treatment with antimicrobials. More data on host susceptibility, stress factors, immune response and infectious dose levels are required. The impact of asymptomatic carriers, M. bovis survival in the environment and the role of wildlife in transmitting the disease also needs investigation. To facilitate development of vaccines, further analysis of more M. bovis genomes, its pathogenic mechanisms, including variable surface proteins, is required, along with reproducible disease models.

Effects of dexamethasone and Mycoplasma bovis on bovine neutrophil function in vitro

It is well established that exposure either to elevated levels of glucocorticoids, or to Mycoplasma bovis (M. bovis), has a negative effect on bovine neutrophil function. The objective of this research was to determine whether in vitro treatment of bovine neutrophils by M. bovis strains (n=4) and glucocorticoids would additively impair phagocyte function. Twenty, healthy, dairy cows were enrolled. Whole blood was collected from all cows for neutrophil isolation. Phagocytosis and the generation of superoxide anion (O2(-)) were tested in vitro by incubation of neutrophils with FITC labeled Escherichia coli (E. coli) and cytochrome c after treatment. Treatments included: NM1-4D (neutrophils treated with dexamethasone and exposed to one of the four M. bovis strains); NM1-4 (neutrophils exposed to one of the four M. bovis strains only); ND (neutrophils treated with dexamethasone only); and N (non-treated control neutrophils). The overall percentages of neutrophils phagocytizing E. coli were: 32%, 51%, 37%, and 53% ± 5.25% for treatments NM1-4D, NM1-4, ND, and N, respectively. The overall statistically transformed means of phagocytized E. coli per neutrophil were: 1.37, 1.72, 1.33, and 1.67 ± 0.057 for treatments NM1-4D, NM1-4, ND, and N, respectively. The overall statistically transformed means of neutrophil O2(-) production were: 8.60, 11.91, 9.01, and 12.21 ± 0.21 nmol/10(6) for treatments NM1-4D, NM1-4, ND, and N, respectively. Exposure of neutrophils to M. bovis plus dexamethasone had an additive effect on generation of reactive oxygen species (p=0.0057), but not on the percentage of neutrophils phagocytizing E. coli (p=0.0817) or number of E. coli phagocytized per neutrophil (p=0.2946). Only one of the four M. bovis strains had a negative effect on neutrophil phagocytic function. Dexamethasone treatment consistently decreased neutrophil function as indicated by decreased percentage of neutrophils phagocytizing E. coli, decreased number of E. coli phagocytized per neutrophil, and decreased neutrophil O2(-) production, compared to controls (p<0.0001). Results suggested a synergistic effect of in vitro incubation of glucocorticoids and M. bovis on reduction of bovine neutrophil function as measured by generation of reactive oxygen species. These findings may explain in part the interaction between stressful events and outbreak of Mycoplasma bovis associated bovine disease.

Mycoplasma bovis Infections in young calves

Mycoplasma bovis has emerged as an important pathogen of young intensively reared calves in North America. A variety of clinical diseases are associated with M bovis infections of calves, including respiratory disease, otitis media, arthritis, and some less common presentations. Clinical disease associated with M bovis often is chronic, debilitating, and poorly responsive to antimicrobial therapy. Current control measures are centered on reducing exposure to M bovis through contaminated milk or other sources, and nonspecific control measures to maximize respiratory defenses of the calf. This article focuses on the clinical and epidemiologic aspects of M bovis infections in young calves.

Mycoplasma Mastitis: A Review of Transmission and Control

The Mycoplasma sp. that cause mastitis are simple, cell wall-less, bacteria that can colonize and cause diseases in other extramammary sites in the bovine. Prevalence of mycoplasma mastitis appears to be increasing in many locations throughout the world. The best method to identify this group of pathogens is through direct culture on mycoplasma agar media. However, limitations with this culture procedure are the duration of culture, 10 days, special conditions required and thus added expense, and the lack of primary specificity to distinguish between true pathogens and commensal organisms. Thus culture of bulk tank milk samples has been advocated as a primary screening method to determine the mycoplasma status of a herd. This monitoring system is reasonably successful but the sensitivity of detection of Mycoplasma sp. in bulk tank milk is affected by a significant minority of cows that might shed the organism at levels below the threshold of detection. Contagious mastitis control procedures have been effective in controlling outbreaks of mycoplasma mastitis. Yet new methods of control might be warranted, methods that may prevent the outbreak. Current data suggests that a significant number of new outbreaks may occur via internal or animal-to-animal transmission of mycoplasma mastitis pathogens from asymptomatic carriers.

Mycoplasma bovis-associated suppurative otitis media and pneumonia in bull calves

Outbreaks of Mycoplasma bovis-associated otitis media and pneumonia occurred on four beef cattle farms in Hokkaido, Japan between 2000 and 2001. The morbidity and mortality were estimated at 8-40 and 30-100%, respectively. Eight calves with bilateral ear droop and exudative otitis media were examined bacteriologically and histopathologically. M. bovis was isolated post mortem from nasal swabs and from the ears, lungs, lymph nodes (cranial and pulmonary), brain and heart of all calves. At necropsy, suppurative exudates were observed in the tympanic bullae of all cases. Numerous abscesses were also found in the petrous portion of the temporal bone and lungs in seven cases. Histopathologically, the exudates within the tympanic bullae consisted of a mixture of neutrophils, necrotic cell debris and fibrin, and the tympanic mucosa was thickened with neutrophil and macrophage infiltration and proliferation of fibrous connective tissue. Pulmonary lesions included extensive foci of coagulative necrosis surrounded by numerous neutrophils. Hepatocytes or renal tubular epithelial cells were enlarged with hyaline cytoplasmic inclusions in four calves. Immunohistochemical labelling confirmed the presence of M. bovis antigen in the cytoplasm of the inflammatory cells in the middle ear, temporal bone and lungs, and was also demonstrated within the cytoplasmic inclusions of the hepatocytes and renal tubular epithelial cells. Ultrastructurally, mycoplasma-like organisms, 200-500 microm in diameter, were found within not only hepatocytes and renal tubular epithelia but also within axons of the facial nerves. The present results show that M. bovis spreads to multiple organs and is capable of invading various kinds of host cell. The intracellular localization may be favourable for evading host immune responses.

An experimental infection model for reproduction of calf pneumonia with bovine respiratory syncytial virus (BRSV) based on one combined exposure of calves

Bovine respiratory syncytial virus (BRSV) has been recognised as an important pathogen in calf pneumonia for 30 years, but surprisingly few effective infection models for studies of the immune response and the pathogenesis in the natural host have been established. We present a reproducible experimental infection model for BRSV in 2-5-month-old, conventionally reared Jersey calves. Thirty-four colostrum-fed calves were inoculated once by aerosol and intratracheal injection with BRSV. Respiratory disease was recorded in 91% of the BRSV-inoculated calves, 72% had an accompanying rise in rectal temperature and 83% exhibited >5% consolidation of the lung tissue. The disease closely resembled natural outbreaks of BRSV-related pneumonia, and detection of BRSV in nasal secretions and lung tissues confirmed the primary role of BRSV. Nine mock-inoculated control calves failed to develop respiratory disease. This model is a valuable tool for the study of the pathogenesis of BRSV and for vaccine efficacy studies.

The efficacy of modified-live bovine respiratory syncytial virus vaccines in experimentally infected calves

The efficacy of modified-live (MLV) bovine respiratory syncytial virus (BRSV) vaccines and the correlates of vaccine-induced immunity were investigated in calves using a virulent experimental infection. Clinical disease and pulmonary pathology were significantly reduced, relative to unvaccinated controls, in calves vaccinated according to label directions with commercial multivalent MLV BRSV vaccines. In vitro assays of cellular immunity were more consistent correlates of vaccine associated protection than presence of post vaccination serum antibody. Most vaccinated calves shed virus, but peak virus titre was suppressed compared to unvaccinated controls, with clearance coincident with the simultaneous appearance of mucosal antibody, cytotoxic cells in the lung and anamnestic or primary serum antibody responses. Virus clearance in unvaccinated calves was coincident with the appearance of BRSV specific cytotoxic cells, before mucosal antibody was detected.