Bacteriological, serological, pathological and immunohistochemical studies of Mycoplasma bovis respiratory infection in veal calves and adult cattle at slaughter

MBOVJF4278_00820 encodes a novel cytoadhesin of Mycoplasma bovis binding to heparin

Mycoplasma bovis, a minimal bacterium but a notorious cattle pathogen, leads to serious economic losses. This pathogen binding to host cells is emerging as a complex process involving a broad range of surface-exposed structures. For mycoplasma, adhering to host tissue is the first and crucial step of infection. It is well known that the molecules contributing to microbial cytoadhesion are important virulence factors. Here, we cloned, expressed, and purified the recombinant protein, which is encoded by MBOVJF4278_00820, and induced polyclonal antibodies for it in mice. The cytoadhesive properties of this surface-exposed protein were demonstrated on embryonic bovine lung (EBL) and Madin-Darby bovine kidney (MDBK) cells. Furthermore, heparin as the binding target was confirmed, and the characteristics of the interaction between this protein and heparin have also been analyzed. Our data indicate that the surface-associated MBOVJF4278_00820-encoded protein is a novel adhesion-related factor of Mycoplasma bovis.IMPORTANCEAdhesins are crucial in facilitating Mycoplasma bovis infection. In this study, we identified a specific Mycoplasma bovis adhesin that interacts with heparin on the surface of host cells. Given that heparin is ubiquitously distributed across a wide range of tissue cells, the identification of the heparin-binding adhesin is significant for elucidating how Mycoplasma bovis targets diverse host cells and triggers a spectrum of clinical manifestations.

Alteration in Tracheal Morphology and Transcriptomic Features in Calves After Infection with Mycoplasma bovis

Mycoplasma bovis is one of the most important pathogens in animal husbandry, and the current infection and morbidity rates are increasing year by year, causing great losses to the farming industry and seriously affecting animal welfare. In this study, we took tracheal tissues from calves infected with M. bovis to make pathological tissue sections for observation, and selected tracheal tissues for transcriptome sequencing to screen differentially expressed genes based on the threshold |log2FoldChange| > 1 and Padjust < 0.05 and functional enrichment, to explore in depth the potential mechanisms of bovine tracheal damage caused by bovine tracheitis. Experiments were conducted to observe the changes in tracheal tissues after M. bovis infection through pathological sections of the trachea of M. bovis-infected calves. From the transcriptome sequencing results, we mined the main differential genes and important metabolic pathways of M. bovis causing damage to the trachea of calves. It was found that the cricoid cartilage tissue of the trachea was congested and hemorrhagic after M. bovis infection in calves, and the pathological sections showed localized necrosis of epithelial cells, disorganization, high inflammatory cell infiltration in the interepithelial and lamina propria, and some epithelial cell detachment. Transcriptome sequencing identified 4199 DEGs, including 1378 up-regulated genes and 2821 down-regulated genes. KEGG enrichment analysis indicated that the differential genes were enriched to 59 significantly differing signaling pathways, and a number of important metabolic pathways related to tracheitis induced by M. bovis-infected calves were unearthed. The major ones included IL-17, the Toll-like receptor, JAK/STAT, the PI3K-Akt signaling pathway, etc. In this study, we found that M. bovis infection of calves caused inflammatory damage to the trachea, and transcriptome sequencing results also showed significant differences in the expression of key genes such as IL-6 inflammatory factor, CASP8, and APOA1.

Mycoplasma bovis 5'-nucleotidase is a virulence factor conferring mammary fitness in bovine mastitis

Nucleases and 5' nucleotidase (5'-NT) play essential roles in cell biology and are often associated with bacterial virulence. In Mycoplasma spp., which have limited metabolic capacities and rely on nutrient availability, these enzymes are of significant importance for nucleotide salvage. This study explores the potential role of 2 membrane-associated lipoproteins, the major nuclease MnuA and 5'-NT, in Mycoplasma bovis mastitis. Mutants deficient in MnuA (mnuA::Tn) and in 5'-NT (0690::Tn) were identified through genome-wide transposon mutagenesis of M. bovis PG45 type strain and their fitness and virulence were assessed both in vitro, in axenic medium, and in vivo, using murine and cow mastitis models. The mnuA::Tn mutant demonstrated reduced nuclease activity, while 0690::Tn exhibited slow log-phase growth and impaired hydrolase activity towards nucleotides as well as deoxynucleotides (dAMP and dGMP). In comparison to the parent strain, the 0690::Tn mutant displayed markedly reduced fitness, as evidenced by a significant decrease or even absence in post-challenge mycoplasma counts in murine and cow mammary tissues, respectively. Moreover, the 0690::Tn mutant failed to induce mastitis in both experimental models. Conversely, the mnuA::Tn mutant induced inflammation in murine mammary glands, characterized by neutrophil infiltration and increased expression of major inflammatory genes. In cows, the mnuA::Tn was able to cause an increase in somatic cell counts in a manner comparable to the wild type, recruit neutrophils, and induce mastitis. Collectively, these findings provide complementary insights, revealing that disruption of 5'-NT significantly attenuated M. bovis pathogenicity, whereas a MnuA-deficient mutant retained the ability to cause mastitis.

Molecular characterisation of Mycoplasma bovis isolates from consecutive episodes of respiratory disease on Dutch veal farms

Mycoplasma bovis infections are wide spread in veal calf farms and a major contributor to respiratory disease. M. bovis are genetically diverse. It is unclear how this diversity influences the virulence and epidemiology of infections on veal calf farms over time. Therefore, the aim of this study was to follow the genetic composition of M. bovis isolates on veal farms over time in a fattening round and combine this with presence of disease and presence of other respiratory pathogens. For this, M. bovis isolates were obtained from healthy and diseased calves from ten different farms at different episodes of respiratory disease in the same groups in one fattening round. A new episode of respiratory disease was defined by the practitioner based on clinical diagnosis at least 7 days after end of a previous metaphylactic treatment. These isolates were sequenced using Illumina sequencing and analysed. This resulted in 148 sequenced isolates. The isolates belonged to 9 different clusters and to the known MLST sequence types ST4 (n=9), ST6 (n=2), ST7 (n=1), ST8 (n=1), ST21 (n=32), ST29 (n=30), ST32 (n=1), ST100 (n=36), ST122 (n=17) and ST135 (n=4), and new sequence types ST222 (n=8), ST223 (n=1), ST224 (n=5) and ST225 (n=1). Major sequence types are linked to types, found in other European countries. All farms showed presence of two or more different clusters, however with different distribution patterns. Farms did not show a major shift in type distribution over time. There was a relationship between M. bovis type and region of origin of the calves and the types differed with regards of presence of variable membrane surface lipoprotein (Vsp) genes. Types were not related to disease status of the calves or presence of other major respiratory pathogens. This study underlines the complexity of M. bovis infection on veal calf farms with persistent presence of different types together in both healthy and diseased calves with or without other respiratory pathogens. Prevention of introduction of M. bovis and biosecurity measures combined with optimisation of calf resilience should have priority.

Mycoplasma bovis-associated verminous pneumonia in alpine chamois (Rupicapra rupicapra)

Pneumonia is a common disease affecting Alpine chamois. However, little is known concerning the etiological agents involved. We investigated whether Mycoplasma spp. infection occurs in Alpine chamois and describe the microscopic lesions associated with Mycoplasma-associated bronchopneumonia in this species. Lung tissues obtained from 45 chamois with gross evidence of pneumonia were analysed. The histological lesions and the presence of lungworms within the lungs were evaluated blindly. The presence of Mycoplasma spp. was assessed by immunohistochemistry (Mycoplasma bovis and Mycoplasma mycoides subsp. mycoides) and by end-point PCR. M. bovis was detected by immunohistochemistry and confirmed by PCR and sequencing in 6/45 (13%) cases, while all lungs were negative for M. mycoides subsp. mycoides. A significant association was found between the detection of M. bovis and the presence of severe lungworms infection in the examined lungs. We report for the first time M. bovis as a bacteria associated with verminous pneumonia in chamois.

Neglected bacterial infections associated to bovine respiratory disease in lactating cows from high-yielding dairy cattle herds

Bovine respiratory disease (BRD) is a multifactorial and predominantly multietiological disease that affects dairy cattle herds worldwide, being more frequent in young animals. The occurrence of BRD was investigated in lactating cows from two high-yielding dairy herds in southern Brazil. To determine the etiology of the clinical cases of acute respiratory disease, nasal swab samples were collected from cows with clinical signs of BRD and evaluated using PCR and RT-PCR for nucleic acid detection of the main BRD etiological agents, including Mycoplasma bovis, Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, bovine respiratory syncytial virus, bovine coronavirus, bovine viral diarrhea virus, bovine alphaherpesvirus 1, and bovine parainfluenza virus 3. Only three microorganisms (M. bovis, H. somni, and P. multocida) were identified in both single and mixed infections. We concluded that 40.0% of the cows were infected with M. bovis and 75.0% with H. somni in herd A. Considering both single and mixed infections, the analyses performed in herd B showed that 87.5%, 25.0%, and 50.0% of the cows were infected with M. bovis, H. somni, and P. multocida, respectively. M. bovis and H. somni are considered fastidious bacteria and laboratory diagnosis is neglected. Subsequently, most clinical cases of mycoplasmosis and histophilosis in cattle remain undiagnosed. This study demonstrates the importance of M. bovis and H. somni infections in adult cows with BRD. These results highlight the importance of including these bacteria in the group of etiological agents responsible for the occurrence of BRD in cattle, especially in adult cows with unfavorable immunological conditions, such as recent calving and peak lactation.

Diagnostic and Prognostic Value of Clinical Scoring and Lung Ultrasonography to Assess Pulmonary Lesions in Veal Calves

This study on veal calf respiratory disease assessed the association between an on-farm clinical scoring system and lung ultrasonography with the postmortem inspection of the lungs. The comparisons allowed the calculation of predictive values of the diagnostic methods. In total, 600 calves on an Austrian veal calf farm were examined at the beginning and the end of the fattening period. Overall, the area under the curve (AUC) for ultrasonographic scores was 0.90 (rsp = 0.78) with a sensitivity (Se) of 0.86. The specificity (Sp) was 0.78, and the positive predictive value (PPV) was 0.74. The AUC for the physical examination was 0.76 (rsp = 0.55) with a Se of 0.64, an Sp of 0.81, and a PPV of 0.69. For the combination of ultrasonography and physical examination, an AUC curve of 0.85 (rsp = 0.69) was calculated. A Se of 0.65 and a Sp of 0.88 with a PPV of 0.73 was calculated. This study concluded that both physical and ultrasonographic examination scoring are reliable examination methods for the detection of lung diseases in veal calves.

EFSA Panel on Animal Health and Animal Welfare (AHAW), Nielsen SS, Alvarez J, Bicout DJ, Calistri P, Canali E, Drewe JA, Garin‐Bastuji B, Gonzales Rojas JL, Gortazar Schmidt C, Herskin M, Michel V, Miranda Chueca MA, Padalino B, Pasquali P, Roberts HC, Spoolder H, Stahl K, Velarde A, Viltrop A, Jensen MB, Waiblinger S, Candiani D, Lima E, Mosbach‐Schulz O, Van der Stede Y, Vitali M, Winckler C. Welfare of calves

This Scientific Opinion addresses a European Commission request on the welfare of calves as part of the Farm to Fork strategy. EFSA was asked to provide a description of common husbandry systems and related welfare consequences, as well as measures to prevent or mitigate the hazards leading to them. In addition, recommendations on three specific issues were requested: welfare of calves reared for white veal (space, group housing, requirements of iron and fibre); risk of limited cow–calf contact; and animal‐based measures (ABMs) to monitor on‐farm welfare in slaughterhouses. The methodology developed by EFSA to address similar requests was followed. Fifteen highly relevant welfare consequences were identified, with respiratory disorders, inability to perform exploratory or foraging behaviour, gastroenteric disorders and group stress being the most frequent across husbandry systems. Recommendations to improve the welfare of calves include increasing space allowance, keeping calves in stable groups from an early age, ensuring good colostrum management and increasing the amounts of milk fed to dairy calves. In addition, calves should be provided with deformable lying surfaces, water via an open surface and long‐cut roughage in racks. Regarding specific recommendations for veal systems, calves should be kept in small groups (2–7 animals) within the first week of life, provided with ~ 20 m²/calf and fed on average 1 kg neutral detergent fibre (NDF) per day, preferably using long‐cut hay. Recommendations on cow–calf contact include keeping the calf with the dam for a minimum of 1 day post‐partum. Longer contact should progressively be implemented, but research is needed to guide this implementation in practice. The ABMs body condition, carcass condemnations, abomasal lesions, lung lesions, carcass colour and bursa swelling may be collected in slaughterhouses to monitor on‐farm welfare but should be complemented with behavioural ABMs collected on farm.

Geography, niches, and transportation influence bovine respiratory microbiome and health

Bovine respiratory disease (BRD), one of the most common and infectious diseases in the beef industry, is associated with the respiratory microbiome and stressors of transportation. The impacts of the bovine respiratory microbiota on health and disease across different geographic locations and sampling niches are poorly understood, resulting in difficult identification of BRD causes. In this study, we explored the effects of geography and niches on the bovine respiratory microbiome and its function by re-analyzing published metagenomic datasets and estimated the main opportunistic pathogens that changed after transportation. The results showed that diversity, composition, structure, and function of the bovine nasopharyngeal microbiota were different across three worldwide geographic locations. The lung microbiota also showed distinct microbial composition and function compared with nasopharyngeal communities from different locations. Although different signature microbiota for each geographic location were identified, a module with co-occurrence of Mycoplasma species was observed in all bovine respiratory communities regardless of geography. Moreover, transportation, especially long-distance shipping, could increase the relative abundance of BRD-associated pathogens. Lung microbiota from BRD calves shaped clusters dominated with different pathogens. In summary, geography, sampling niches, and transportation are important factors impacting the bovine respiratory microbiome and disease, and clusters of lung microbiota by different bacterial species may explain BRD pathogenesis, suggesting the importance of a deeper understanding of bovine respiratory microbiota in health.

Prevalence of Mycoplasma bovis in Algeria and Characterisation of the Isolated Clones

Bovine respiratory disease (BRD) is common in calves in Algeria, but to date, Mycoplasma bovis has never been monitored as a potential etiological agent. Here, to assess the presence (direct detection) and circulation (indirect detection) of M. bovis, broncho-alveolar lavage fluids (BALF) and serum samples were collected from 60 veal calf farms in Algeria. A commercial ELISA kit (ID Screen^® ELISA) was used to screen for the presence of specific antibodies against M. bovis in 351 blood sera collected from both diseased and healthy calves, and 69% (241 sera) tested positive. BALFs from the 176 diseased calves were used to screen for M. bovis by real-time-PCR (rt-PCR), and 102 (58%) tested positive. A non-exhaustive set of 53 clones were isolated from 44 calves and further subtyped using polC gene sequencing. No predominant subtype was found, and two clones exhibited a new subtype. Fourteen clones were further characterized by multilocus sequence typing, and results showed a high degree of genetic diversity, with some clones having new alleles and subtypes. The minimum inhibitory concentrations (MICs) of 5 antimicrobials regularly used to treat BRD was determined on 45 clones. Susceptibility profiles showed very broad diversity, confirming the variety of clones actively circulating. We detected clones with high MICs, including increased MICs of enrofloxacin (n = 5). This is the first study to report the presence of M. bovis in Algeria in calves with BRD. This research also finds broad genetic and phenotypic diversity in the actively circulating isolates.

Mycoplasma bovis May Travel Along the Eustachian Tube to Cause Meningitis in Japanese Black Cattle

Mycoplasma bovis (M. bovis) is a common inhabitant of the upper and lower respiratory tracts of cattle and is considered to be the main aetiological agent of otitis media in calves. The eustachian tube appears to be the most common portal for pathogens to enter the middle ear. We investigated the transmission route of M. bovis causing otitis media that progressed to meningitis or meningoencephalitis in Japanese Black cattle. M. bovis was detected in 10 cases by a loop-mediated isothermal amplification method or by immunohistochemistry. One case of caseonecrotic granulomatous meningoencephalitis, one case of caseonecrotic granulomatous meningitis, one case of suppurative meningoencephalitis, eight cases of eustachitis, nine cases of tonsillitis and six cases of suppurative bronchopneumonia were identified by histopathological examination. M. bovis antigen was detected in the eustachian tubes of eight cases. In nine cases, M. bovis was also detected in tonsillar epithelial crypts and lumina, in intraluminal inflammatory cells and in the epithelial cells of minor salivary glands located around the eustachian tubes and tonsils. The results suggest that M. bovis can infect and colonize the tonsils and enter the eustachian tubes, causing otitis media, which, in cases of chronic infection, can progress to meningitis.

Identification of Mycoplasma species and related organisms from ruminants in England and Wales during 2005-2019

Background

Mycoplasma species have been associated with economically important diseases affecting ruminants worldwide and include contagious bovine pleuropneumonia (CBPP), contagious caprine pleuropneumonia (CCPP) and contagious agalactia, listed by the World Organisation for Animal Health (OIE). The Mycoplasma Team at the Animal and Plant Health Agency provides an identification service for Mycoplasma and Ureaplasma species of veterinary importance to the United Kingdom (UK), supporting the detection of new and emerging pathogens, as well as contributing to the surveillance of endemic, and the OIE listed diseases exotic to the UK. Mycoplasma and other Mollicutes species were identified from diagnostic samples from farmed ruminants in England and Wales using a combination of culture and 16S rRNA gene-based PCR-denaturing gradient gel electrophoresis, submitted between 2005 and 2019.

Results

A total of 5578 mollicutes identifications, which include mycoplasmas and the related acholeoplasmas and ureaplasmas, were made from farmed ruminant animals during the study period. Throughout the study period, the pathogen Mycoplasma bovis was consistently the most frequently identified species, accounting for 1411 (32%) of 4447 molecular identifications in cattle, primarily detected in the lungs of pneumonic calves, followed by joints and milk of cattle showing signs of arthritis and mastitis, respectively. M. bovirhinis, M. alkalescens, M. dispar, M. arginini and Ureaplasma diversum, were also common. Mixed species, principally M. bovis with M. alkalescens, M. arginini or M. bovirhinis were also prevalent, particularly from respiratory samples. The non-cultivable blood-borne haemoplasmas Candidatus ‘Mycoplasma haemobos’ and Mycoplasma wenyonii were identified from cattle, with the latter species most often associated with milk-drop. M. ovipneumoniae was the predominant species identified from sheep and goats experiencing respiratory disease, while M. conjunctivae preponderated in ocular samples. The UK remains free of the ruminant mycoplasmas listed by OIE.

Conclusions

The continued high prevalence of M. bovis identifications confirms its ongoing dominance and importance as a significant pathogen of cattle in England and Wales, particularly in association with respiratory disease. M. ovipneumoniae has seen a general increase in prevalence in recent years, notably in coughing lambs and should therefore be considered as a primary differential diagnosis of respiratory disease in small ruminants.

Fatal Calf Pneumonia Outbreaks in Italian Dairy Herds Involving Mycoplasma bovis and Other Agents of BRD Complex

Mycoplasma bovis is increasingly recognized worldwide as an important cause of disease with major welfare and production impairments on cattle rearing. Although it was detected in veal calves and beef cattle, little is known on the infection impact and on its temporal morbidity pattern in Italian dairy herds. Thus, this study aimed to investigate the involvement of M. bovis on fatal calf pneumonia outbreaks that occurred during 2009–2019 in 64 Italian dairy farms. Furthermore, a deeper diagnostic workup of concurrent infection with other viral and bacterial respiratory pathogens was assessed. Out of the investigated fatal pneumonia cases, M. bovis was frequently detected (animal prevalence, 16.16%; 95%CI, 11.82–21.33; herd prevalence, 26.56; 95%CI, 16.29–39.08) either as the single agent of the disease in more than half of the positive samples (20/37) or in concurrent infections with Histophilus somni (9/37, 24.3%), Mannheimia haemolytica (6/37, 16.621%), Trueperella pyogenes (1/37, 2.70%), Pasteurella multocida (1/37, 2.70%), bovine respiratory syncytial virus (5/37, 13.51%), and bovine viral diarrhea virus (2/37, 5.55%). Based on time-series analysis, M. bovis was recorded in the area since 2009 with outbreaks displaying a clear morbidity seasonal pattern with peaks in April (43.21%) and in September (13.51%). This might be due to the stressing conditions during spring and late summer periods. Results of this study highlight that M. bovis infection warrants consideration, and control measures are needed given its involvement in lethal pneumonia outbreaks in dairy herds from an extended area.

Evaluation of inter-rater agreement of the clinical signs used to diagnose bovine respiratory disease in individually housed veal calves

In dairy calves raised for veal, typical clinical signs of bovine respiratory disease (BRD) are ocular discharge, nasal discharge, ear droop or head tilt, abnormal respiration, cough, and increased rectal temperature. Despite the existence of several clinical scoring systems, there are few studies on the variability of human recognition of individual BRD clinical signs. The objective of this study was therefore to assess the inter-rater agreement of BRD clinical signs in veal calves. We hypothesized that BRD clinical signs were not detected equally between veterinarians, technicians, and producers of the veal industry and that some clinical signs have higher inter-rater agreement than others. During 2017-2018, we prospectively recorded 524 videos of physical examinations of random veal calves from 48 different batches in Québec, Canada. A researcher, not involved in the inter-rater assessment, classified each video as presence/absence of each BRD clinical sign except rectal temperature. For each of the 5 clinical signs, 15 videos with and 15 videos without the clinical signs were randomly selected to avoid kappa paradoxes. Those 30 videos were then presented in a random order to experienced raters of BRD in veal calves: 6 veterinarians, 6 technicians, and 6 producers. The raters assessed the clinical signs using scores based on the Wisconsin and California scoring system with modifications (0 = absent, 1 = mild, 2 = moderate, 3 = severe for nasal discharge, ocular discharge, and ear droop or head tilt; and 0 = absent, 1 = moderate, 2 = severe for abnormal respiration and induced cough). We used median percentage agreement (Pa), median Cohen's kappa (κ), and Gwet's agreement coefficient 1 (AC1) to assess inter-rater agreement. The effect of scale combination was also tested to determine the optimal combination (4-scale 0/1/2/3 vs. 3-scale 0/1/2 vs. 2-scale 0/1,2,3; 0,1/2,3; or 0/1,2). The differences of inter-rater agreement between veterinarians, technicians, and producers were estimated by a Wilcoxon rank-sum test. The 2-scale combination (0,1/2,3 or 0/1,2) had the highest inter-rater agreement for all clinical signs. With this combination, induced cough was the clinical sign with the highest inter-rater agreement (Pa = 0.93; κ = 0.79; AC1 = 0.87) and abnormal respiration was the sign with the lowest inter-rater agreement (Pa = 0.77; κ = 0.20; AC1 = 0.74). According to Pa and AC1 values, the 2-scale inter-rater agreement of the 5 clinical signs was good (value > 0.6). According to κ, only ear droop or head tilt and induced cough had a substantial 2-scale inter-rater agreement (κ > 0.6). In general, the 2-scale inter-rater agreement was better among veterinarians than among technicians and producers, except for the ear droop/head tilt, where agreement was better among producers. We concluded that with severity scores assessed on a scale of 2 (0,1/2,3 or 0/1,2), the inter-rater agreement of BRD clinical signs was variable according to the sign in veal calves. BRD clinical signs were not detected equally between veterinarians, technicians, and producers of the veal industry. Future research could determine if this discrepancy could be improved by standardization training.

Application of Four Genotyping Methods to Mycoplasma bovis Isolates Derived from Western Canadian Feedlot Cattle

Mycoplasma bovis is a significant pathogen of feedlot cattle, responsible for chronic pneumonia and polyarthritis syndrome (CPPS). M. bovis isolates (n = 129) were used to compare four methods of phylogenetic analysis and to determine if the isolates' genotypes were associated with phenotypes. Metadata included the health status of the animal from which an isolate was derived (healthy, diseased, or dead), anatomical location (nasopharynx, lung, or joint), feedlot, and production year (2006 to 2018). Four in silico phylogenetic typing methods were used: multilocus sequence typing (MLST), core genome MLST (cgMLST), core genome single nucleotide variant (cgSNV) analysis, and whole-genome SNV (wgSNV) analysis. Using Simpson's diversity index (D) as a proxy for resolution, MLST had the lowest resolution (D = 0.932); cgSNV (D = 0.984) and cgMLST (D = 0.987) generated comparable results; and wgSNV (D = 1.000) provided the highest resolution. Visual inspection of the minimum spanning trees found that the memberships of the clonal complexes and clades had similar structural appearances. Although MLST had the lowest resolution, this methodology was intuitive and easy to apply, and the PubMLST database facilitates the comparison of sequence types across studies. The cg methods had higher resolution than MLST, and the graphical interface software was user-friendly for nonbioinformaticians, but the proprietary software is relatively expensive. The wgSNV approach was the most robust for processing poor-quality sequence data while offering the highest resolution; however, application of its software requires specialized training. None of the four methods could associate genotypes with phenotypes.

Importance and Antimicrobial Resistance of Mycoplasma bovis in Clinical Respiratory Disease in Feedlot Calves

Simple Summary

Bovine respiratory disease is a common health and economic problem that mainly affects calves raised in feedlots. Several viruses and bacteria may be involved, but Mycoplasma bovis can cause disease chronification and poor response to antimicrobial treatment. This study investigated the role of Mycoplasma bovis in cases of clinical respiratory disease unresponsive to treatment that affected feedlot calves in southeast Spain, and tested the in vitro susceptibility of a selection of isolates to the specific set of antimicrobials used for therapy in vivo. Mycoplasma bovis was found in 86.9% (20/23) of the calves, predominantly in the lungs (78.26%; 18/23) where it was involved in pulmonary lesions. Furthermore, the selected isolates were found to be resistant in vitro to most of the antimicrobials specifically used for treating the animals in vivo. These results highlight the implication of Mycoplasma bovis in the bovine respiratory disease affecting feedlot calves in Spain.

Abstract

Bovine respiratory disease (BRD) is an important viral and/or bacterial disease that mainly affects feedlot calves. The involvement of Mycoplasma bovis in BRD can lead to chronic pneumonia poorly responsive to antimicrobial treatment. Caseonecrotic bronchopneumonia is a pulmonary lesion typically associated with M. bovis. In Spain, M. bovis is widely distributed in the feedlots and circulating isolates are resistant to most antimicrobials in vitro. However, the role of this species in clinical respiratory disease of feedlot calves remains unknown. Furthermore, available data are relative to a fixed panel of antimicrobials commonly used to treat BRD, but not to the specific set of antimicrobials that have been used for treating each animal. This study examined 23 feedlot calves raised in southeast Spain (2016–2019) with clinical signs of respiratory disease unresponsive to treatment. The presence of M. bovis was investigated through bacteriology (culture and subsequent PCR), histopathology and immunohistochemistry. The pathogen was found in 86.9% (20/23) of the calves, mainly in the lungs (78.26%; 18/23). Immunohistochemistry revealed M. bovis antigens in 73.9% (17/23) of the calves in which caseonecrotic bronchopneumonia was the most frequent lesion (16/17). Minimum inhibitory concentration assays confirmed the resistance of a selection of 12 isolates to most of the antimicrobials specifically used for treating the animals in vivo. These results stress the importance of M. bovis in the BRD affecting feedlot calves in Spain.

Production Significance of Bovine Respiratory Disease Lesions in Slaughtered Beef Cattle

Bovine respiratory disease (BRD) is still a serious concern in feedlots, where it exerts a negative effect on farm productivity. There is a shortage of studies focused on the evaluation of BRD-associated lesions at the slaughterhouse in clinically healthy animals. The objective of this work was to investigate the prevalence and type of subclinical pneumonic lesions in slaughtered beef cattle, according to the age range and management system, and its impact on carcass weight. A total of 1101 beef cattle intended for human consumption were examined at slaughter. Information on age, sex, management system and carcass weight was recorded. The presence and type of pneumonia were evaluated according to gross and microscopic findings and etiological agents by PCR. Lung pneumonic lesions appeared in 17.9% of animals and were predominant among veal calves. According to the type, chronic catarrhal pneumonia prevailed in the majority of animals, and mixed and extensively reared cattle were more likely to suffer acute fibrinous pneumonia. The presence of pneumonic lesions was associated with a significant decrease in carcass weight that had more of an impact in veal male calves coming from intensive systems. Bacterial infections were the predominant infectious agent and the only cause of acute fibrinous pneumonia, while viruses were infrequent and only found in lesions with chronic catarrhal pneumonia. This study shows the importance of BRD in beef feedlots upon production values and points out the feasibility of slaughterhouse assessment of pneumonia as a method for the evaluation of BRD significance.

Expression profiling of microRNAs in the Mycoplasma bovis infected mammary gland tissue in Holstein Friesian cattle

The immune response associated with mastitis caused by Mycoplasma bovis is a very complicated biological process in several type of cells, including immune cells, mammary epithelial cells, and endothelial cells. Thus, revealing of the microRNAs in the Mycoplasma bovis infected mammary gland tissues is particularly important for the immune response mechanism to Mycoplasma bovis. Firstly, 20 mammary gland tissue samples were collected from Holstein Friesian cattle that was located in Erzurum province at 2018 and screened for Mycoplasma bovis. Then, total RNA was isolated from Mycoplasma bovis infected tissues and high-throughput sequencing was performed. After bioinformatics analysis, GO and KEGG analysis of target genes of identified microRNAs were conducted. In this study, a total of 616 microRNAs were found. Our results revealed that 24 of the known microRNAs were expressed differently and 13 of the novel microRNAs were expressed differently in Mycoplasma bovis positive tissues. The target genes of these microRNAs were found to be associated with especially inflammation pathways, including B cell and T cell receptor signaling, Fc gamma R-mediated, phagocytosis/chemokine signaling, and MAPK signaling. In conclusion, this study demonstrated that identified miRNAs may be involved in the signaling pathways during mastitis caused by Mycoplasma bovis.

Mycoplasma bovis in Spanish Cattle Herds: Two Groups of Multiresistant Isolates Predominate, with One Remaining Susceptible to Fluoroquinolones

Mycoplasma bovis is an important bovine pathogen causing pneumonia, mastitis, and arthritis and is responsible for major economic losses worldwide. In the absence of an efficient vaccine, control of M. bovis infections mainly relies on antimicrobial treatments, but resistance is reported in an increasing number of countries. To address the situation in Spain, M. bovis was searched in 436 samples collected from beef and dairy cattle (2016–2019) and 28% were positive. Single-locus typing using polC sequences further revealed that two subtypes ST2 and ST3, circulate in Spain both in beef and dairy cattle, regardless of the regions or the clinical signs. Monitoring of ST2 and ST3 isolates minimum inhibitory concentration (MIC) to a panel of antimicrobials revealed one major difference when using fluoroquinolones (FQL): ST2 is more susceptible than ST3. Accordingly, whole-genome sequencing (WGS) further identified mutations in the gyrA and parC regions, encoding quinolone resistance-determining regions (QRDR) only in ST3 isolates. This situation shows the capacity of ST3 to accumulate mutations in QRDR and might reflect the selective pressure imposed by the extensive use of these antimicrobials. MIC values and detection of mutations by WGS also showed that most Spanish isolates are resistant to macrolides, lincosamides, and tetracyclines. Valnemulin was the only one effective, at least in vitro, against both STs.

Infection Dynamics of Mycoplasma bovis and Other Respiratory Mycoplasmas in Newly Imported Bulls on Italian Fattening Farms

Italian beef production is mainly based on a feedlot system where calves are housed with mixed aged cattle often in conditions favourable to bovine respiratory disease (BRD). In Veneto, an indoor system is also used for imported bulls around 300–350 kg. Mycoplasmas, in particular Mycoplasma bovis and Mycoplasma dispar, contribute to BRD in young calves, but their role in the disease in older cattle has not been investigated. In this study, ten heads of cattle were selected from each of the 24 groups kept in 13 different farms. Bulls were sampled by nasal swabbing at 0, 15, and 60 days after arrival for Mycoplasma isolation. Identification was carried out by 16S-rDNA PCR followed by denaturing gradient gel electrophoresis. M. bovis, M. dispar, and M. bovirhinis were identified, and prevalence was analysed by mixed-effects logistic regression models. This showed that most bulls arrived free of M. bovis, but within two weeks, approximately 40% became infected, decreasing to 13% by the last sampling. In contrast, the prevalence of M. dispar was not dependent on time or seasonality, while M. bovirhinis only showed a seasonality-dependent trend. The Italian fattening system creates an ideal environment for infection with M. bovis, probably originating from previously stabled animals.

Intracellular Localization of Mycoplasma bovis in the Bronchiolar Epithelium of Experimentally Infected Calves

Lung tissues from calves infected experimentally with Mycoplasma bovis were examined by immunohistochemistry and electron microscopy. All inoculated calves had dark red areas of consolidation affecting both left and right lungs, which were characterized microscopically by subacute purulent bronchiolitis with hyperplasia of the surrounding lymphoid tissue. Immunohistochemically, M. bovis antigen was detected on the surface and inside the cytoplasm of bronchiolar epithelial cells in the pneumonic foci. The antigen was also found in the cytoplasm of phagocytes at the margin of bronchiolar exudates. Electron microscopically, numerous organisms were demonstrated in the immunohistochemically-positive sites. These findings suggest that M. bovis organisms adhere to the bronchiolar epithelium and at least some of them invade the epithelium.

Pathology and immunohistochemical evaluation of lungs of cattle slaughtered at metropolitan abattoirs in Nigeria and Ghana

There was a dearth of information on pathology and causal agents of bovine pneumonia in West Africa. This cross-sectional study conducted at four major metropolitan abattoirs in Nigeria and Ghana was to evaluate the pathology and to immunohistochemically demonstrates viral and bacterial pathogens of bovine pneumonia in West Africa. Out of the 20,605 cattle lungs examined at post-mortem using standard inspection procedures, 136 samples grossly showed pneumonic lesions and 99 randomly selected lung samples were fixed in 10% neutral buffered formalin for histopathological and immunohistochemical examination. The overall prevalence of pneumonia was 0.66%, with 0.72% prevalence in Ibadan, Nigeria and 9.68% prevalence in Ghana. Age and breed were observed to be among the predisposing factors to pneumonia in cattle. Histologically, bronchopneumonia (0.65%), broncho-interstitial pneumonia (0.13%), and interstitial pneumonia (0.08%) were the prominent type of pneumonias observed. Immunohistochemically, 0.8% was positive for bovine PI-3, 0.9% for bovine RSV, 1.0% for Mannheimia haemolytica (MH), and 0.6% for Pasteurella multocida (PM). There were a few interactions of pathogens: PI3 and MH (0.01%), RSV and MH (0.01%), PM and MH (0.02%). This was the first study that immunohistochemically demonstrated bacterial and viral antigens in naturally occurring pneumonia in cattle in Nigeria and Ghana.

Antimicrobial Sensitivity Testing of Mycoplasma bovis Isolates Derived from Western Canadian Feedlot Cattle

Mycoplasma bovis is particularly adept at evading the immune system, resulting in chronic infections of the lungs and joints of feedlot cattle. The chronicity of the lesions results in prolonged antimicrobial therapy, possibly exacerbating antimicrobial resistance. This cross-sectional study generated in vitro antimicrobial susceptibility testing (AST) data on 211 M. bovis isolates recovered from 159 healthy, diseased, and dead cattle, spanning the period of 2006-2018. Nine antimicrobials commonly administered to western Canadian feedlot cattle were assessed. The data were analyzed with non-parametric statistical tests with a level of significance of p < 0.05 (two-tailed). Minimum inhibitory concentration (MIC) values tended to increase between the isolates from healthy versus dead cattle and over time (2006-2018). Isolates from dead versus healthy cattle were more likely to be resistant to tulathromycin, gamithromycin, tylosin and enrofloxacin. There was no difference in the distributions of the MICs generated from the isolates recovered from the lungs and joints (p ≥ 0.124) and the lungs and deep nasal passages (p ≥ 0.157) of the same animals.

Biosecurity practices in Belgian veal calf farming: Level of implementation, attitudes, strengths, weaknesses and constraints

The shift from cure toward prevention in veterinary medicine involves the implementation of biosecurity. In cattle farming, the application of biosecurity measures has been described to a limited degree, yet no data on biosecurity on veal farms is available. A high degree of commingling of veal calves from multiple farms causes frequent disease outbreaks, and thereby high antimicrobial usage and increased risk of antimicrobial resistance. Therefore, this study aimed to describe the current implementation of biosecurity on veal farms in Belgium. To this extent, a list of the most important calf diseases (n = 34) was created, and risk factors and related biosecurity measures for these diseases were determined and included in a questionnaire. Herd visits and face-to-face interviews were conducted on 20 randomly selected veal farms, comprising 8.3% of the target population. A categorical principal component and clustering analysis were performed to determine the influence of the veal companies on the farms' biosecurity level. Awareness of biosecurity was very low among the farmers. All farms used an "all-in, all-out" production system with calves originating from multiple farms without quarantine. On average, farms were filled in 11.4 days (range 2-52). The degree of commingling for these farms was 1.24, meaning that, on average, 124 calves originated from 100 farms. Veterinarians wore farm-specific boots on eight farms (40%) and farm-specific clothes on six farms (30%), while technical advisors wore farm-specific boots on six farms (30%) and farm-specific clothes on four farms (20%). Disinfection footbaths were only used in five farms (25%) despite being present in all farms in the sample. Concerning internal biosecurity, none of the farmers isolated sick animals; only one farmer (5%) had a physically separated hospital pen, and only 11 farmers (55%) both cleaned and disinfected the stables after each production cycle. In most farms, animals were of comparable age. Healthy calves generally remained in the same compartment during the entire production cycle, limiting the risks associated with the movement of animals. No influence of the integrations on the biosecurity level could be determined. It can be concluded that a few biosecurity measures, such as "'all-in, all-out" and compartmentation, are implemented relatively well, while other measures, such as good cleaning and disinfection and proper entrance measures for visitors and personnel can easily be improved. The improvement of measures regarding the introduction of animals of different origins will require more fundamental changes in the veal industry.

Relationship between bronchoalveolar lavage fluid and plasma endotoxin activity in calves with bronchopneumonia

The aim of this study was to investigate the relationship between the endotoxin activity in plasma and that in bronchoalveolar lavage fluid (BALF) in bronchopneumonia. Thirty-three calves were included in this study (17 healthy calves and 16 calves with respiratory disease). In the calves with bronchopneumonia, the median endotoxin activity in plasma (0.437 EU/ml, P<0.001) and BALF (29.45 EU/ml, P<0.001) was significantly higher than in the control calves. Plasma endotoxin activity was significantly and positively correlated with that in BALF (r²=0.900, P<0.001). Based on the receiver operating characteristics curves, we propose a diagnostic cutoff point for plasma endotoxin activity (0.104 EU/ml, AUC=0.914, P<0.001, Se 81.3% and Sp 82.4%) for identification of bronchopneumonia in calves which could die within a week.

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.

Evaluating Potential Biomarkers of Health and Performance in Veal Calves

Veal calves undergo many challenges in the early stages of their life. Such challenges, including mixing procedures and transportation of calves to the veal farm, may have a negative influence on growth rate, feed intake, metabolism, immunity and disease susceptibility of calves. As a consequence, many hematological, physiological, metabolic and immunological parameters of stressed calves might be altered on arrival at the veal farm. Some of these response variables might be useful as biomarkers of performance of calves at the veal farm as they might provide information about an ongoing disease process, or may predict future diseases. Biomarkers might be helpful to group and manage calves in different risk categories after arrival. By adopting treatment decisions and protocols on a risk-group or individual basis, it would be possible to improve animal health and reduce both disease incidence and antibiotic use. Moreover, the use of biomarkers might be an economically feasible approach as some of them do not need invasive techniques and others can be measured in blood already taken during routine checks. Previous literature mainly assessed the physiological responses of calves to transportation. However, information on the link between on-farm arrival data and future health and performance of veal calves is limited. This review, therefore, examined a wide range of papers and aimed to identify potential biomarkers of future health and performance.

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.

DNA microarray assay and real-time PCR as useful tools for studying the respiratory tract Mycoplasma populations in young dairy calves

PURPOSE

With more than 120 species, the genus Mycoplasma is one of the largest taxa in the class Mollicutes, a group of micro-organisms that are characterized by apparent simplicity and to which important animal pathogens belong. Mycoplasmabovis is the most frequently identified pathogenic Mycoplasma in cattle; however, the prevalence of other Mycoplasma species living in calves' airways is poorly understood. The aim of this work was to characterize the respiratory tract mycoplasma populations in calves on one of the largest dairy farms in Italy using a real-time PCR assay and a DNA microarray assay.

METHODOLOGY

A total of 49 nasal swabs and 49 trans-tracheal aspirations from non-vaccinated veal calves were analysed. Genomic DNA was extracted from the samples and then tested using a real-time PCR targeting the oppD gene of M. bovis and a DNA microarray that was able to identify more than 70 Mycoplasma species.

RESULTS

Forty-two out of 49 calves tested positive for Mycoplasma spp. (85.7 %). None of the samples tested positive for M. bovis. A majority (73.5 %) of the 98 samples tested positive for M. dispar, while 8 samples tested positive for M. bovirhinis (8.2 %).

CONCLUSION

Our results expand our knowledge regarding the diversity of Mycoplasma populations in the respiratory airways of very young veal calves and add data regarding M. bovis prevalence in the Italian cattle population. However, the importance of these species in the respiratory diseases of calves still remains to be determined.

A register-based study of the antimicrobial usage in Danish veal calves and young bulls

High antimicrobial usage and multidrug resistance have been reported in veal calves in Europe. This may be attributed to a high risk of disease as veal calves are often purchased from numerous dairy herds, exposed to stress related to the transport and commingling of new animals, and fed a new ration. In this study, we used national register data to characterize the use of antimicrobials registered for large Danish veal calf and young bull producing herds in 2014.

A total of 325 herds with veal calf and potentially young bull production were identified from the Danish Cattle database. According to the national Danish database on drugs for veterinary use (VetStat), a total of 537,399 Animal Daily Doses (ADD₂₀₀) were registered for these 325 herds during 2014. The amount of antimicrobials registered in 2014 varied throughout the year, with the highest amounts registered in autumn and winter. Antimicrobials were registered for respiratory disorders (79%), joints/limbs/CNS disorders (17%), gastrointestinal disorders (3.7%) and other disorders (0.3%). Of the registered antimicrobials, 15% were for oral and 85% for parenteral administration. Long-acting formulations with a therapeutic effect of more than 48 h covered 58% of the drugs for parenteral use. Standardized at the herd-level, as ADD₂₀₀/100 calves/day, antimicrobial use distributed as median [CI_95%] for starter herds (n = 22): 2.14 [0.19;7.58], finisher herds (n = 24): 0.48 [0.00;1.48], full-line herds (n = 183): 0.78 [0.05;2.20] and herds with an inconsistent pattern of movements (n = 96): 0.62 [0.00;2.24]. Full-line herds are herds, which purchase calves directly from a dairy herd and raise them to slaughter.

Furthermore, we performed a risk factor analysis on the 183 herds with a full-line production. Here, we investigated, whether the number of suppliers, the number of calves purchased, the frequency of purchase, the average age at introduction, the average time in the herd and vaccination influenced the amount of antimicrobials used in the herds. The final multivariable regression analysis revealed that the number of calves introduced was positively associated with the antimicrobial use in the herd.

Profiles of serum amino acids to screen for catabolic and inflammation status in calves with Mycoplasma bronchopneumonia

The aim of the present study was to investigate the relationships between serum amino acid profiles in normal and calves with Mycoplasma bronchopneumonia. Serum free amino acid concentrations in serum obtained from 34 calves with or without Mycoplasma bronchopneumonia were determined by high-performance liquid chromatography. The calves with Mycoplasma were characterized by significantly lower total amino acid and total essential amino acid concentrations and molar ratios of branched-chain amino acid (BCAA) to aromatic amino acid (BCAA/AAA) and BCAA to tyrosine (BTR), and by a significantly higher molar ratio of serine phosphorylation (SPR). The proposed diagnostic cutoffs for BCAA/AAA, BTR and SPR in serum based on ROC analysis for detection of catabolic states associated with Mycoplasma bronchopneumonia were set at <1.75, <2.86 and >0.85, respectively. Our results suggest that determining the profiles of amino acids, especially BTR and SPR, could provide useful diagnostic information in terms of predicting protein catabolism in Mycoplasma bronchopneumonia.

Overall decrease in the susceptibility of Mycoplasma bovis to antimicrobials over the past 30 years in France

Mycoplasma (M.) bovis is frequently implicated in respiratory diseases of young cattle worldwide. Today, to combat M. bovis in Europe, only antimicrobial therapy is available, but often fails, leading to important economical losses. The antimicrobial susceptibility of M. bovis is not covered by antimicrobial resistance surveillance networks. The objectives of this study were to identify resistances that were acquired over the last 30 years in France and to determine their prevalence within contemporary strains. The minimum inhibition concentration (MIC) values of 12 antimicrobials, considered active on M. bovis, were compared, using an agar dilution method, between 27 and 46 M. bovis isolates respectively obtained in 1978-1979 and in 2010-2012 from 73 distinct respiratory disease outbreaks in young cattle all over France. For eight antimicrobials, resistances were proven to be acquired over the period and expressed by all contemporary strains. The increase of the MIC value that inhibited 50% of the isolates (MIC50) was: i) substantial for tylosin, tilmicosin, tulathromycin and spectinomycin, from 2 to >64, 2 to >128, 16 to 128 and 4 to >64 µg/mL, respectively, ii) moderate for enrofloxacin, danofloxacin, marbofloxacin and oxytetracycline, from 0.25 to 0.5, 0.25 to 0.5, 0.5 to 1, 32 to >32 µg/mL, respectively. No differences were observed for gamithromycin, tildipirosin, florfenicol and valnemulin with MIC50 of 128, 128, 8, <0.03 µg/mL, respectively. If referring to breakpoint MIC values published for respiratory bovine pathogens, all contemporary isolates would be intermediate in vivo for fluoroquinolones and resistant to macrolides, oxytetracycline, spectinomycin and florfenicol.

Mycoplasma bovis infection in respiratory disease of dairy calves less than one month old

Mycoplasma bovis is an important cause of bovine respiratory disease, especially in young calves where it can also cause arthritis, tenosynovitis and otitis. During 2009 and 2010 a survey was carried out on carcasses of calves less than one month old sent to the Diagnostic Laboratory of the Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna in Brescia, regardless of the presence of lung lesions, to detect this pathogen. PCR tests for Mycoplasma spp. and M. bovis were applied. 83 out of 224 (37%) lung tissue samples examined were positive at PCR test for Mycoplasma spp.; in 64 cases of these we observed typical respiratory lesions (P<0.001). M. bovis was identified in 26 out of 83 (31%) lung tissue samples positive at PCR test for Mycoplasma spp.; in 24 cases of these we observed typical respiratory lesions (P=0.039). Our data demonstrate that presence of Mycoplasma spp. and M. bovis positively correlates with pneumonic lung lesions in young dairy calves.

Prevalence of respiratory disorders in veal calves and potential risk factors

The study aimed to assess the in vivo and postmortem prevalence of respiratory disorders in veal calves and investigate risk factors associated with them. A cross-sectional study was carried out in 174 farms in the 3 major veal meat-producing countries in Europe (50 in France, 100 in the Netherlands, and 24 in Italy). Trained veterinarians visually evaluated individual calves of 1 batch per farm at 3 and 13 wk after arrival and at 2 wk before slaughter to assess the prevalence of hampered respiration, nasal discharge, and coughing. A random sample of lungs belonging to calves of the same batch was monitored at the slaughterhouse for mild to moderate or severe signs of pneumonia, and presence of pleuritis. Data regarding veal calf housing, feeding, and management and specific characteristics of the batch were collected through an interview with the stockperson, and the potential of these as respiratory disease risk factors was assessed. Regardless of the stage of fattening, the prevalence of in vivo signs of respiratory disorders in calves was always <7%. This low prevalence was likely the outcome of the general implementation by veal producers of standardized practices such as prophylaxis, all-in/all-out, and individual daily checks of the calves, which are recognized tools for effective disease prevention and management. However, at postmortem inspection, 13.9% and 7.7% of lungs showed mild to moderate and severe signs of pneumonia, respectively, and 21.4% of the inspected lungs had pleuritis. Thus, even mild clinical signs of respiratory disorder in calves at specific time points during the fattening period may be associated with high prevalence of lungs with lesions at slaughter. Alternatively, clinical symptoms recorded during routine visual inspections of veal calves on-farm may be poor predictors of the true prevalence of respiratory disease in calves. Among all potential risk factors considered, those concerning the characteristics of the batch were predominant but factors related to housing, management and feeding equipment were also relevant. Different risk factors were involved at different stages of the fattening period. Therefore, to overcome respiratory disorders in veal calves, different solutions may apply to different stages of the fattening period.

Coronavirus infection in intensively managed cattle with respiratory disease

Background

A detailed laboratory investigation identified bovine coronavirus (BCoV) as the aetiological agent in an outbreak of respiratory disease at a semi‐intensive beef cattle feedlot in south‐east Australia. The outbreak caused 30% morbidity in the resident population and also affected two cohorts of cattle that were newly introduced to the property.

Methods

At slaughter, pulmonary consolidation and inflammatory lesions in the trachea were identified in 15 of 49 animals. Pasteurella multocida or Histophilus somni was cultured from 3 of 7 animals with lesions. Histopathological examination revealed multifocal non‐suppurative bronchointerstitial pneumonia with formation of epithelial syncytial cells, sometimes associated with suppurative bronchopneumonia.

Results

BCoV was detected in nasal swabs and pulmonary lesions using real‐time reverse transcriptase–polymerase chain reaction (qRT‐PCR) assay and virus isolation. There was serological evidence of previous exposure to bovine viral diarrhoea virus, bovine respiratory syncytial virus and bovine parainfluenza virus type 3, but not to bovine herpesvirus type 1. None of these viral pathogens or Mycoplasma bovis was identified by qRT‐PCR.

Conclusion

This is believed to be the first report of BCoV in association with bovine respiratory disease complex in Australia.

α-Enolase, an adhesion-related factor of Mycoplasma bovis

Mycoplasma bovis is the causative agent of Mycoplasma bovis-associated disease (MbAD). Although the mechanisms underlying M. bovis adherence to host cells is not clear, recent studies have shown that the cell surface protein α-enolase facilitates bacterial invasion and dissemination in the infected host. In this study, we cloned, expressed and purified recombinant M. bovis α-enolase and induced polyclonal anti-α-enolase antibodies in rabbits. M. bovis α-enolase was detected in the cytoplasmic and membrane protein fractions by these antibodies. Triple immunofluorescence labeling combined with confocal laser scanning microscopy (CLSM) revealed that the plasminogen (Plg) enhanced the adherence of M. bovis to embryonic bovine lung (EBL) cells; the values obtained for adherence and inhibition are consistent with this finding. Interestingly, we found that trace amounts of trypsin acted as a more effective enhancer of cell adherence than Plg. Hence, our data indicate that surface-associated M. bovis α-enolase is an adhesion-related factor of M. bovis that contributes to adherence by binding Plg.

Histochemical and morphometric characterization of broncho-pneumonia in calves caused by infection with Mycoplasma bovis

The aim of this study was to identify morphometric histological features of pneumonia caused by Mycoplasma bovis in calves. Eight three-month-old calves were infected with M. bovis and samples of their lung tissue, three weeks after exposure, compared to samples from four uninfected calves. In the uninfected animals the goblet cells were clustered in the crypt area of the epithelial folds, while in the infected calves they had migrated towards the tips of the folds and were distributed evenly throughout the folds. In infected lung tissue there was goblet cell hyperplasia and metaplasia in the bronchioles and an increased epithelial height. Goblet cell mucin in uninfected calves was acidic, but in infected calves most goblet cells contained neutral mucins. These morphometric and histochemical bronco-epithelial changes may be able to be used as markers of the severity of bovine respiratory mycoplasmosis.

Chronic pneumonia in calves after experimental infection with Mycoplasma bovis strain 1067: characterization of lung pathology, persistence of variable surface protein antigens and local immune response

Background

Mycoplasma bovis is associated with pneumonia in calves characterized by the development of chronic caseonecrotic lesions with the agent persisting within the lesion. The purposes of this study were to characterize the morphology of lung lesions, examine the presence of M. bovis variable surface protein (Vsp) antigens and study the local immune responses in calves after infection with M. bovis strain 1067.

Methods

Lung tissue samples from eight calves euthanased three weeks after experimental infection with M. bovis were examined by bacteriology and pathology. Lung lesions were evaluated by immunohistochemical (IHC) staining for wide spectrum cytokeratin and for M. bovis Vsp antigens and pMB67 antigen. IHC identification and quantitative evaluation of CD4⁺ and CD8⁺ T lymphocytes and immunoglobulin (IgG1, IgG2, IgM, IgA)-containing plasma cells was performed. Additionally, expression of major histocompatibility complex class II (MHC class II) was studied by IHC.

Results

Suppurative pneumonic lesions were found in all calves. In two calves with caseonecrotic pneumonia, necrotic foci were surrounded by epithelial cells resembling bronchial or bronchiolar epithelium. In all calves, M. bovis Vsp antigens were constantly present in the cytoplasm of macrophages and were also present extracellularly at the periphery of necrotic foci. There was a considerable increase in numbers of IgG1- and IgG2-positive plasma cells among which IgG1-containing plasma cells clearly predominated. Statistical evaluation of the numbers of CD4⁺ and CD8⁺ T cells, however, did not reveal statistically significant differences between inoculated and control calves. In M. bovis infected calves, hyperplasia of bronchus-associated lymphoid tissue (BALT) was characterized by strong MHC class II expression of lymphoid cells, but only few of the macrophages demarcating the caseonecrotic foci were positive for MHC class II.

Conclusions

The results from this study show that infection of calves with M. bovis results in various lung lesions including caseonecrotic pneumonia originating from bronchioli and bronchi. There is long-term persistence of M. bovis as demonstrated by bacteriology and immunohistochemistry for M. bovis antigens, i.e. Vsp antigens and pMB67. The persistence of the pathogen and its ability to evade the specific immune response may in part result from local downregulation of antigen presenting mechanisms and an ineffective humoral immune response with prevalence of IgG1 antibodies that, compared to IgG2 antibodies, are poor opsonins.

Analysis of trace and major elements in bronchoalveolar lavage fluid of Mycoplasma bronchopneumonia in calves

The aim of this study was to evaluate the reliability and effectiveness of direct determination of trace and major element concentrations in bronchoalveolar lavage fluid samples from Holstein calves with Mycoplasma bronchopneumonia (n = 21) and healthy controls (n = 20). The samples were obtained during bronchoscopy using a standard examination method. A total of 18 elements (aluminum, bromine, calcium, chlorine, chromium, copper, iron, potassium, magnesium, manganese, molybdenum, nickel, phosphorous, sulfur, silicon, strontium, titanium, and zinc) were detected by particle-induced X-ray emission. The average bromine, iron, potassium, magnesium, and phosphorous concentrations were higher in calves with bronchopneumonia than in controls (p < 0.05). They were found to have higher amounts of calcium and zinc, and a higher zinc-copper ratio than that in healthy calves (p < 0.001). Based on the receiver operating characteristics curves, we propose a diagnostic cutoff point for zinc-copper ratio for identification of Mycoplasma pneumonia of 8.676. Our results indicate that assessment of the elemental composition of broncholaveolar lavage fluid is a promising diagnostic tool for Mycoplasma bronchopneumonia.

Bovine mycoplasmosis: silent and deadly

The first international conference on bovine mycoplasmosis, held in Saskatoon, Canada, in 2009, marked an official recognition of the importance of mycoplasmas in bovine respiratory disease, mastitis, arthritis and other disorders. Furthermore, bovine mycoplasmosis has been identified as a major emerging infectious disease by the European Community 7th Framework Programme under the EMIDA ERA-NET, which is funding a three-year study into the development of improved diagnosis and control of bovine mycoplasmosis involving the UK, Germany, Italy and Israel. These developments coincide with the publication of the complete sequence of the Mycoplasma bovis genome, which offers fresh insight into the properties of this tiny wall-less bacterium. With this in mind, it is an appropriate time to review our knowledge of cattle diseases caused by mycoplasmas.

Outbreak of bovine clinical mastitis caused by Mycoplasma bovis in a North Italian herd

This report describes an outbreak of Mycoplasma bovis mastitis affecting 45 cows in a herd of 122 dairy cattle in Northern Italy. Clinically, the outbreak was characterized by agalactia, multiple swollen and painless quarters, high milk somatic cell count and unresponsiveness to conventional antibiotic therapy. M. bovis was isolated from the milk samples of all the 32 affected cows tested and from the mammary tissue of three affected cows that underwent necropsy. No other pathogens were isolated from these samples. Lesions in two of the necropsied cows were characterized by mild chronic suppurative mastitis and galactophoritis. The other necropsied cow showed a chronic necrosuppurative and pyogranulamaous galactophoritis, a condition not previously associated with M. bovis. M. bovis was detected immunohistochemically in the lumen of the affected mammary ducts suggesting that ascending infection via the teat canal was the likely route of transmission. No other intralesional pathogens were demonstrated microscopically.