Experimental exposure of cattle to a precise aerosolised challenge of Mycobacterium bovis: a novel model to study bovine tuberculosis.

Non-aerosol models of bovine tuberculosis are limited in reproducibility and relevance to natural cases seen in farmed animals. Therefore, there is a need for aerosol models of infection in cattle that can reproduce bovine tuberculosis as seen in natural cases of the disease. This manuscript describes a cattle tuberculosis model based on the inhalation of a precisely defined dose of Mycobacterium bovis in aerosol form, and defines those sites of M. bovis deposition following aerosol inhalation. The dissemination of bacilli and the resultant pathological change following infection is also described. Cattle aged 4-5 months, were infected with approximately 10(4) colony forming units (CFU), using a Madison chamber that had been modified to deliver aerosols to calves. In Experiment 1, calves were examined for gross pathology at post mortem (PM) examination at 93 and 132 days post-infection (PI), respectively. In Experiment 2, pairs of calves were examined for gross pathology at PM examination at 1 day PI and 7 days PI, respectively. At PM examination, samples were taken for bacteriology. Retrospective counts showed that the calves inhaled between 3 x 10(4) and 8 x 10(4)CFU of M. bovis. In Experiment 1, pathology indicative of tuberculosis and detection of M. bovis by qualitative bacteriology was found throughout the lower respiratory tract (LRT). In Experiment 2, pathology was only observed in a single site of one calf at day 7 PI. Samples positive for M. bovis by bacteriology were predominantly in the LRT. The numbers of M. bovis CFU recovered and the distributions of positive sites were greater at day 7 PI than day 1 PI. This study describes an aerosol exposure method that can deliver a defined dose of M. bovis almost exclusively to the LRT. The distribution of M. bovis and lesions indicative of tuberculosis suggests this aerosol method replicates the primary mode of tuberculosis transmission in cattle.

Shedding of Mycobacterium bovis in the nasal mucus of cattle infected experimentally with tuberculosis by the intranasal and intratracheal routes.

Four groups of six calves were infected experimentally with either a low dose of approximately 10(4) colony-forming units (cfu) or a high dose of approximately 10(6) cfu of Mycobacterium bovis. Each dose was delivered by the intranasal and intratracheal routes. More severe disease was observed in the groups inoculated with the high dose. Visible lesions were identified in 21 of the 24 animals, all of which also gave positive skin tests and interferon-gamma (IFN-gamma) responses. Nasal shedding was detected in 15 of the 24 animals and the frequency of shedding was influenced by both the route and the dose of infection; no shedding was observed in the group infected intratracheally with the low dose. Two of the 15 confirmed shedders had no visible lesions at postmortem examination; both of these calves gave IFN-gamma responses but only one was skin test positive.

The role of WC1(+) gamma delta T-cells in the delayed-type hypersensitivity (DTH) skin-test reaction of Mycobacterium bovis-infected cattle.

Delayed-type hypersensitivity (DTH) skin-testing with mycobacterial antigens is often used as a means of identifying Mycobacterium bovis-infected cattle. Better understanding of the cellular basis underlying the DTH reaction is required if diagnostic methods are to be improved upon. Previous studies have shown that gamma delta T-cells, particularly those bearing the WC1 molecule, are present at an early stage of developing DTH responses and that such cells may modulate the developing immune response immediately following M. bovis-infection. However, their role, if any, in the DTH response remains unclear. In the present study we have used an in vivo model to deplete WC1(+) gamma delta T-cells, from cattle with established M. bovis-infection, prior to skin-testing. Results indicate that, although WC1(+) gamma delta T-cells do infiltrate the skin-test site in normal calves, they do not appear to be essential for the development of DTH skin swelling, as indicated by effective development of skin responses in calves depleted of circulating WC1(+) gamma delta T-cells.

Pathogenesis of tuberculosis in cattle.

There has been a renewed interest in the pathogenesis of bovine tuberculosis in many countries, in an attempt to understand better its transmission, to improve diagnosis and assess the potential of vaccination. This paper, which overviews current knowledge of aspects of the pathogenesis of bovine tuberculosis, draws from studies of field cases and experimental infections and highlights deficiencies in current understanding. The pathogenesis of bovine tuberculosis has not received the same level of attention as with human tuberculosis, and in many instances, the processes involved in bovine tuberculosis have been drawn from studies of human tuberculosis or from small animal models of infection. This paper however, considers the successful emulation of naturally acquired tuberculosis using experimental cattle models and identifies the complex and integrated nature of microbiological, immunological and pathological events involved. Current understanding of the initiation of infection, immune responses, and subsequent pathology, which can vary significantly in individual animals are discussed. Whilst there are aspects of M. bovis that still remain elusive to scientific investigation, further studies on the pathogenesis of bovine tuberculosis are advocated as necessary to provide a better scientific basis on which to review control and eradication strategies, which are currently less than effective in many regions.

Lymphocyte subtypes in experimentally induced early-stage bovine tuberculous lesions.

The identity of the lymphocyte subtypes constituting the lymphocytic mantle within developing early-stage lesions of bovine tuberculosis was investigated immunohistochemically in calves inoculated intranasally with 2 x 10(7) colony-forming units of a field isolate of Mycobacterium bovis. Pulmonary lesions were examined 7, 14, 21, 28 and 42 days after inoculation, and bronchial lymph node lesions at 35 days. The immunolabelling results reported were obtained with monoclonal antibodies against two T-cell epitopes (WC1+ gamma delta and CD2+) and against B-cell epitopes. Large numbers of CD2+ T-lymphocytes were observed around developing areas of necrosis throughout the study; WC1+ gamma delta cells, however, were more numerous at these sites up to and including day 21. On the other hand, aggregates of B lymphocytes did not become prominent in areas adjacent to lesions until day 42. The results suggest that these lymphocyte phenotypes play a role in the pathogenesis of early-stage lesions.

Isolation and characterisation of rhabdovirus from wild common bream Abramis brama, roach Rutilus rutilus, farmed brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss in Northern Ireland.

Rhabdovirus was isolated from wild common bream Abramis brama during a disease outbreak with high mortality in Northern Ireland during May 1998. Rhabdovirus was also isolated at the same time from healthy farmed rainbow Oncorhynchus mykiss and brown trout Salmo trutta on the same stretch of river and 11 mo later from healthy wild bream and roach Rutilus rutilus in the same river system. Experimental intra-peritoneal infection of bream and mirror carp Cyprinus carpio var specularis with 2 of these isolates produced low mortality rates of < or = 12%. Serological testing of these isolates by virus neutralisation indicated that they were antigenically closely related to pike fry rhabdovirus (PFRV) but not to spring viraemia of carp virus (SVCV), while testing by enzyme-linked immunosorbent assay indicated them to be antigenically different from both. Comparison of nucleotide sequence data of a 550 base pair segment of the viral glycoprotein generated by reverse transcription-polymerase chain reaction indicated a high (> or = 96.6%) degree of similarity between these isolates and a previous Northern Ireland isolate made in 1984, a 1997 isolate from bream in the Republic of Ireland and an earlier Dutch isolate from roach. In contrast, similarity between these isolates and PFRV was < 82.4%, indicating that these viruses belong to 2 distinct genogroups, while similarity to SVCV was even lower (< 67.4%).

Effect of parainfluenza-3 virus challenge on cell-mediated immune function in parainfluenza-3 vaccinated and non-vaccinated calves.

A group of four conventional, colostrum-fed calves was vaccinated with live parainfluenza type 3 (PI-3) virus vaccine at 1 and 5 weeks of age. A group of four control calves was treated with cell culture medium at the same time. Two weeks after the second vaccination, both groups of calves were challenged with PI-3 virus by a combined respiratory route. Blood and nasal mucus samples were collected at intervals, and alveolar macrophages were recovered before and after challenge by bronchoalveolar lavage. The results demonstrated that clearance of virus, as indicated by presence of virus antigen was more rapid in previously vaccinated calves. Several alveolar macrophage functions were markedly reduced in all calves 5 to 7 days following virus challenge, although microbicidal activity was unaffected, compared to the controls. The production of neutrophil chemotactic factors by alveolar macrophages occurred more rapidly after virus challenge in the previously vaccinated calves and this correlated with a more rapid neutrophil influx into the lungs in these animals.

The detection of CD2+, CD4+, CD8+, and WC1+ T lymphocytes, B cells and macrophages in fixed and paraffin embedded bovine tissue using a range of antigen recovery and signal amplification techniques.

In order to develop procedures to label the main bovine leucocyte populations in paraffin embedded sections, the immunoreactivity of 25 monoclonal antibodies (mAbs) to different leucocyte antigens was assessed with formal dichromate (FD5) and 10% formalin fixation, a battery of antigen retrieval (AR) methods, and the biotin-tyramide amplification system. All the leucocyte populations investigated (CD2+, CD4+, CD8+, WC1+ T lymphocytes, B cells and macrophages) were strongly and specifically detectable under an appropriate combination of mAb, AR method and signal amplification system. CD4 and CD8 required the most stringent conditions and could only be demonstrated in FD5 fixed sections. For detection of CD2, WC1+ T lymphocytes, B cells and macrophages, all the mAbs produced immunoreactivity in FD5 or formalin fixed tissues. The need to check a range of different AR methods is stressed, as the method of choice varied for each individual mAb. The incorporation of the signal amplification system was necessary to observe a strong signal and the complete distribution of CD4, CD8 and B cells. Fixation by FD5 proved to be better than formalin for the preservation of surface antigens but it was inferior for the detection of markers which were found to show cytoplasmic immunoreactivity, such as the macrophage marker MAC387 or the B cell markers BAQ155 or IL-A59.

Lesions in cattle exposed to Mycobacterium bovis-inoculated calves.

Nine calves were housed for periods ranging from 24 to 117 days in close contact with cattle inoculated intranasally with Mycobacterium bovis. These "in-contact" calves were examined immunologically and bacteriologically during the period of exposure, and pathologically and immunocytochemically post mortem. Three became infected by day 14, as indicated by the detection of M. bovis in nasal mucus. In-vitro interferon-gamma production and lymphocyte proliferation were detected after stimulation of peripheral blood with M. bovis antigens in the majority of in-contact animals by day 28; this provided support for the role of immunological mechanisms in pathogenesis. Tuberculous lesions were found in the submandibular and bronchomediastinal lymph nodes and in the lungs of the in-contact calves; in distribution and appearance the lesions resembled those observed in naturally occurring disease. The distribution of M. bovis antigen and the numbers of mycobacteria within pulmonary lesions are reported. 1999 Harcourt Publishers Ltd.

Studies on the efficacy of intranasal vaccination for the prevention of experimentally induced parainfluenza type 3 virus pneumonia in calves.

The efficacy of intranasal vaccination in preventing or limiting disease of the lower respiratory tract induced by parainfluenza 3 (PI3) virus was evaluated under experimental conditions, using a commercially available live vaccine containing a temperature-sensitive strain of PI3 virus. In a preliminary study four colostrum-deprived calves were vaccinated intranasally at one week and again at two months of age, and two similar calves were given an intranasal placebo. After the second vaccination serum antibodies to PI3 virus were detected in all four vaccinated calves, but not in the control animals. Seventeen days after the second vaccination all six calves were challenged with virulent PI3 virus, and they were killed six days later. The clinical scores and the extent of pulmonary consolidation were reduced in the vaccinated animals; PI3 virus was detected in the upper and lower respiratory tract of the control calves but in none of the vaccinated calves. In a larger scale study with 14 colostrum-fed calves, seven were vaccinated at one week and again at five weeks of age, and seven were given an intranasal placebo. Two weeks after the second vaccination all 14 calves were challenged with virulent PI3 virus. The clinical scores and lung consolidation were significantly reduced in the vaccinated calves in comparison with the controls. Six days after infection, 10 of the 14 calves were killed; PI3 virus was detectable in the nasal secretions of all seven control calves but in only one of the vaccinated animals, and PI3 viral antigen was detected in the lungs of the control calves but not in those of the vaccinated animals. One of the vaccinated calves had developed a severe clinical response after the challenge, but it had only minor lung consolidation when killed.

Tonsillar lesions in cattle naturally infected with Mycobacterium bovis.

The upper respiratory tract surfaces, the palatine and pharyngeal tonsils and associated lymph nodes of 32 tuberculin reactor cattle were examined pathologically and bacteriologically. Tuberculous lesions were observed histologically in the palatine tonsils of five animals and in both the palatine and pharyngeal tonsils of a sixth. Mycobacterium bovis was cultured from the tonsils of four of these animals and from the palatine or pharyngeal tonsils of a further eight cattle in which no lesions were observed. The upper respiratory tract surfaces of 10 animals were M bovis-positive.

Early lesion formation in cattle experimentally infected with Mycobacterium bovis.

Early lesion formation was examined in 13 calves inoculated intranasally with 2 x 10(7) colony-forming units of Mycobacterium bovis and killed either singly or in pairs at intervals of < or = 7 days from post-inoculation day (pid) 3 to pid 42. Immunological examinations were carried out before and after infection, and sequential necropsies were performed. M. bovis was recovered as early as pid 3, from the upper respiratory tract mucosae, retropharyngeal lymph nodes and caudal lung lobe. Gross tuberculous lesions were detected in both the upper respiratory tract mucosae and in the lungs of the calves killed from pid 14 onwards. Lesions were also present in the lymph nodes draining these areas. On histological examination, neutrophils appeared to play a key role in the earliest stages of lesion formation, and lesion mineralization was observed for the first time at pid 35. The contemporaneous development of lesions and cellular immunity, as demonstrated by in-vitro lymphocyte proliferation and interferon-gamma assay responses, provided further evidence of the role of immunopathogenic mechanisms in the development of bovine tuberculosis.

Bovine serum transferrin concentration during acute infection with Haemophilus somnus.

A novel, competitive immunoassay based on time-resolved fluorimetry was developed, and used to measure the serum concentration of bovine transferrin during acute Haemophilus somnus pneumonia. Upper and lower limits of normality were established using serum from healthy cattle (3.72-1.37 mgmL-1). Following experimental infection with Haemophilus somnus, transferrin concentration was depressed in all calves but recovered to pre-infection levels in groups of calves which had either no lesions, or mild lesions at necropsy between 5 and 6 days after infection. In a third group, which developed extensive lesions, the transferrin concentration remained depressed. Transferrin levels remained within the normal range for all calves during the experimental period. Those calves which had low transferrin concentrations pre-infection, developed extensive lung lesions following experimental infection with Haemophilus somnus.

Evaluation of a competitive immunoassay for the detection of bovine haptoglobin.

A competitive immunoassay to quantify the serum concentration of bovine haptoglobin (hp) using time resolved fluorescence was compared with an indirect method of hp assay (haemoglobin binding assay), using sera taken from healthy animals (n = 158), animals experimentally infected with Haemophilus somnus (n = 10) and from sick animals requiring veterinary treatment (n = 440). Upper limits of normality (for normal animals) were tentatively established for the immunoassay (2.1 micrograms ml-1) and for the haemoglobin binding assay (103 micrograms ml-1). The competitive immunoassay detected elevated hp in 62.5 per cent of field sera by comparison with only 19.2 per cent using the conventional haemoglobin binding assay. Serum albumin concentration did not correlate with hp although concentrations of globulins and copper did correlate. However, these parameters (serum globulin and copper) were found to be insensitive markers of inflammatory disease.

Pathological and immunohistochemical studies of natural and experimental Mycoplasma bovis pneumonia in calves.

Lung tissues from calves naturally and experimentally infected with Mycoplasma bovis were subjected to histopathological and immunohistochemical examination. The latter was carried out with a monoclonal antibody raised against M. bovis, and an avidin-biotin-peroxidase complex (ABC) detection substrate system. Pulmonary lesions in naturally infected calves included exudative bronchopneumonia and extensive foci of coagulative necrosis surrounded by inflammatory cells. Experimentally infected lungs showed suppurative bronchiolitis and varying degrees of peribronchiolar mononuclear cell cuffing. M. bovis antigen in field cases was mainly detected at the periphery of the areas of coagulative necrosis, in necrotic exudates, and in close association with infiltrating macrophages and neutrophils. In lung tissue from calves with induced M. bovis pneumonia, antigen was located in epithelial cells, within inflammatory cells in airway lumina, and in alveolar walls. Other microbiological observations suggested that the ability of M. bovis to invade and cause lung parenchymal damage could be influenced by the participation of other pathogens.

Mortality in cattle up to two years old in Northern Ireland during 1992.

A study of bovine mortality involving a stratified random sample of farms and veterinary practices was carried out in Northern Ireland during 1992. In the farm survey over 3500 deaths were reported from 1069 farms and 237 farms reported no deaths. The estimated total number of deaths of cattle up to two years old was 12,332, a figure which excludes an estimated 7921 stillbirths. The estimated annual mortality rates for six- to 24-month-old cattle, one- to five-month-old calves and neonatal calves were 0.79 per cent, 0.82 per cent and 1.02 per cent respectively. The stillbirth rate was 1.86 per cent. Respiratory syndromes were associated with 37 per cent of the deaths of six- to 24-month-old cattle and gastrointestinal syndromes were associated with 22 per cent; in one- to five-month-old calves these syndromes were associated with 37 and 33 per cent of the deaths, respectively. Stillbirths accounted for 62 per cent of all the deaths of calves under one month old, and the neonatal disease complex accounted for 39 per cent of the deaths of calves which were born alive but died within one month of birth.

A study of mortality among suckler and dairy cows in Northern Ireland in 1992.

As part of an initiative aimed at reducing the number of cattle deaths in Northern Ireland, a survey of bovine mortality on a stratified random sample of farms and veterinary practices was carried out during 1992. In the farm survey, over 3500 deaths were reported from 1069 farms, with a further 237 farms reporting no deaths during the year. The estimated numbers of deaths of suckler cows and dairy cows were 5997 and 4246, respectively, giving an estimated annual mortality rate of 2.36 per cent for suckler cows and 1.55 per cent for dairy cows. One third of the suckler cows and 19 per cent of the dairy cows were found dead with no previous signs of illness. In the cows in which clinical signs were observed and which received veterinary attention, hypomagnesaemia (20.3 per cent) was the main cause of death in suckler cows and coliform mastitis (12.3 per cent) was the single most important cause of death in dairy cows. Conditions associated with calving accounted for approximately 30 per cent of the deaths in both types of cow.

Detection of Mycobacterium bovis infection in skin test-negative cattle with an assay for bovine interferon-gamma.

Mycobacterium bovis was isolated from respiratory secretions and lymph nodes from 15 skin test-negative cattle which exhibited interferon-gamma responses. These field cases, identified by blood testing, constituted a significant proportion of skin test-negative cattle which had been subjected to extensive post mortem examinations. Typical tuberculous lesions were found in seven of them. The consequences of cattle with early tuberculosis infection not being detected by traditional tuberculin testing are considered.

Ultrastructural features of alveolar lesions in induced respiratory syncytial virus pneumonia of calves.

Ultrastructural changes occurred in alveolar epithelium in the acute and repair stages of induced respiratory syncytial virus pneumonia induced in eight calves (calf Nos. 1-7, 3 to 6 days old and calf No. 8, 2 weeks old), using a bovine strain of respiratory syncytial virus. Five of the calves were Friesians, three were Hereford x Friesians, and all were male. Tissues from three mock-infected control calves (two Friesian, one Hereford x Friesian) were also examined. Evidence of respiratory syncytial virus infection was observed in both type I and type II pneumocytes from day 4 to day 8 after infection. Infection of type I pneumocytes frequently resulted in necrosis. The response of type II pneumocytes to respiratory syncytial virus infection varied and included hypertrophy, hyperplasia, and syncytial formation. In some infected type II pneumocytes, there were numerous irregular projections of the cell surface, associated with viral budding. Hypertrophy and hyperplasia of type II pneumocytes, epithelial syncytium formation, and irregular cytoplasmic projections from epithelial cells caused considerable thickening of respiratory membrane and occlusion of alveolar lumina. Neutrophils were frequently observed in close association with virus-infected epithelial cells, but evidence of respiratory syncytial virus infection and replication was not observed in alveolar macrophages or neutrophils. Proliferation of type II pneumocytes appeared to play a major role in maintaining the integrity of the alveolar epithelium during the acute stage of the experimental pneumonia. Increased numbers of type II pneumocytes were present on alveolar walls, particularly from 4 to 8 days after infection, and some alveoli were lined entirely by this cell type. In some areas, however, squamous epithelial cells were also involved in covering exposed alveolar basement membrane.