Mycobacterium bovis in the anterior respiratory tracts in the heads of tuberculin-reacting cattle

Morphology of Naturally-Occurring Tuberculosis in Cattle Caused by Mycobacterium caprae

This study describes the pathomorphological alterations of bovine tuberculosis through gross and histopathological examinations, assessment of the distribution of lesions and the demonstration of mycobacteria. Samples from lungs, liver, small intestine, their regional lymph nodes and retropharyngeal lymph nodes were collected from 84 cattle with tuberculosis from the Allgäu, Germany. Organs were evaluated grossly, histopathologically and by transmission electron microscopy. Mycobacteria and mycobacterial antigens were demonstrated using acid-fast staining and immunohistochemistry (IHC). Bacteriological tests revealed Mycobacterium caprae in all animals. Gross alterations were classified into five patterns (I to V) with an additional pattern of acute exudative pulmonary inflammation (pattern VI). Histological lesions were classified into four types (1-4) with additional lesions occurring in lungs only. Acid-fast staining revealed a low number of bacteria in all tissues, while IHC showed comparatively more mycobacterial antigens within the lesions and also at their periphery. The alimentary tract (68%) was the main portal of entry followed by an aerosol infection (19%). It was assumed that the observed lesions reflect a continuous primary period of infection; there were no lesions typical of a secondary (post-primary) period, as reported in man and also described in the older literature on bovine tuberculosis. The broad spectrum of changes described formerly was not observed in the present cases and the route of infection and nature of acid fast staining showed differences when compared with previous studies of naturally-occurring bovine tuberculosis.

[Interlaboratory test: Isolation of Mycobacterium bovis from granulomatous lesions in bovine]

Mycobacterium bovis is the causative agent of bovine tuberculosis. The diagnostic laboratory confirmation is made through bacterial isolation. The aim of interlaboratory tests is to assess the performance of each participant in comparison with other of similar capacities. The test objective was to determine the efficiency of isolation of M. bovis. Four laboratories were part of the test and processed 25 blind tissue samples from granulomatous lesions and with previous M. bovis isolation. The laboratory that had the highest proportion of isolates was A (68%), followed by C (60%) and then B and D (both with 52%). The greatest concordance was observed between B-D and B-C laboratories (68%). The differences could be due to specific factors in each laboratory procedures. This type of interlaboratory tests highlights errors in the bacteriology and identifies critical points in the process to detect M. bovis accurately.

Comparison of immune peripheral blood cells in tuberculin reactor cattle that are seropositive or seronegative for Mycobacterium bovis antigens

Bovine tuberculosis (bTB) is a major economic problem in animal husbandry and is a public health risk in nonindustrialized countries. It is generally accepted that protection against TB is generated through cell-mediated immunity. Previous investigations have shown that WC1(+) γδ, CD4(+) and CD8(+) T-cell subpopulations are important in the immune response to bTB. It is known that changes in the immune balance from a dominant T helper 1 (Th1)-type response toward a more prominent Th2 response may be observed during disease progression. In this study, we aimed to investigate immune peripheral blood cells in tuberculin reactor cattle that are seropositive or seronegative for Mycobacterium bovis antigens, using flow cytometry and hematological analysis. The evaluation of the T cell subpopulations revealed a decrease in CD8(+) T cells of the seropositive and seronegative animals compared with the control animals (p=0.0001). Moreover, the seropositive group exhibited a lower percentage of CD8(+) T cells than the seronegative group. The percentage of B cells was significantly increased in the seropositive group compared with the seronegative group and the control group (p=0.0009). No difference was observed in the percentage of WC1(+) γδ and CD4(+) T cells among the groups. Furthermore, following 24h of peripheral blood culture with bovine purified protein derivative (PPD), both apparently infected groups showed an increase in the levels of cellular activation compared with the control group (p<0.0001). The seropositive group displayed a higher level of cellular activation than the seronegative group. In both apparently infected groups, the hematological analysis showed an increase in total leukocyte (p=0.0012), lymphocyte (p=0.0057), monocyte (p=0.0010) and neutrophil (p=0.0320) counts in comparison with the healthy animals. Our results demonstrated differences in immune peripheral blood cells of tuberculin reactor cattle that are seropositive or seronegative for M. bovis antigens, probably due to different stages of bTB among the groups. The percentages of CD8(+) T cells, B cells and the T cell activation levels may represent biomarkers for the progression of the disease. However, general characteristics shared by both apparently infected groups as lymphocytosis and monocytosis may also be indicative of the disease. Further experiments are required to understand the variations between cellular and humoral immunities throughout the course of bTB infection. A detailed knowledge of the peripheral blood cells involved in all stages of the bTB immune response of naturally infected cattle is essential for the optimal exploitation of diagnosis and vaccination models.

Differential responses of macrophages from bovines naturally resistant or susceptible to Mycobacterium bovis after classical and alternative activation

It is known that macrophages from naturally resistant animals possess a strong immune response against bovine tuberculosis to control mycobacterial infections. In the present study, the macrophage phagocytic activity, intracellular bacterial survival, and cytokine gene expression induced by classical and alternative activators against Mycobacterium bovis in naturally resistant or susceptible bovines, were evaluated. Animals were classified as naturally resistant or susceptible based on the capacity of their macrophages to allow M. bovis (BCG) growth. Peripheral blood macrophages from naturally resistant and susceptible animals were activated by classical and alternative stimuli and challenged with either non-pathogenic M. bovis BCG strain or pathogenic 9926 strain. Naturally resistant animals showed the highest phagocytosis index and microbial control after classical and alternative stimuli, being this response higher against the strain 9926 than the non-virulent strain. In addition, the response of macrophages activated by the classical pathway was higher than that under the alternative activation against both types of strains. Furthermore, classical pathway-activated macrophages derived from naturally resistant animals expressed higher levels of the pro-inflammatory markers iNOS, IL-1β, TNF-α, MIP-1 and MIP-3, and the anti-inflammatory markers ARGII and TGF-b, particularly to BCG. The results of this study showed that macrophages from naturally resistant animals produced stronger pro-inflammatory responses than those from susceptible ones to signals provided by classical pathway activators. Its role in innate immunity against M. bovis is yet to be determined.

Bovine tuberculosis in African buffaloes: observations regarding Mycobacterium bovis shedding into water and exposure to environmental mycobacteria

BACKGROUND

African buffaloes are the maintenance host for Mycobacterium bovis in the endemically infected Kruger National Park (KNP). The infection is primarily spread between buffaloes via the respiratory route, but it is not known whether shedding of M. bovis in nasal and oral excretions may lead to contamination of ground and surface water and facilitate the transmission to other animal species. A study to investigate the possibility of water contamination with M. bovis was conducted in association with a BCG vaccination trial in African buffalo. Groups of vaccinated and nonvaccinated buffaloes were kept together with known infected in-contact buffalo cows to allow natural M. bovis transmission under semi-free ranging conditions. In the absence of horizontal transmission vaccinated and control buffaloes were experimentally challenged with M. bovis. Hence, all study buffaloes in the vaccination trial could be considered potential shedders and provided a suitable setting for investigating questions relating to the tenacity of M. bovis shed in water.

RESULTS

Serial water samples were collected from the drinking troughs of the buffaloes once per season over an eleven-month period and cultured for presence of mycobacteria. All water samples were found to be negative for M. bovis, but 16 non-tuberculous Mycobacterium spp. isolates were cultured. The non-tuberculous Mycobacterium species were further characterised using 5'-16S rDNA PCR-sequencing, resulting in the identification of M. terrae, M. vaccae (or vanbaalenii), M. engbaekii, M. thermoresistibile as well as at least two species which have not yet been classified.

CONCLUSION

The absence of detectable levels of Mycobacterium bovis in the trough water suggests that diseased buffalo do not commonly shed the organism in high quantities in nasal and oral discharges. Surface water may therefore not be likely to play an important role in the transmission of bovine tuberculosis from buffalo living in free-ranging ecosystems. The study buffalo were, however, frequently exposed to different species of non-tuberculous, environmental mycobacteria, with an unknown effect on the buffaloes' immune response to mycobacteria.

A case study of bovine tuberculosis in an area of County Donegal, Ireland

A descriptive analysis, to investigate the potential risk factors that might have contributed to the increased incidence of bovine tuberculosis (BTB) herd-breakdowns in the reference area of Co. Donegal during the fifth year of the four-area project (FAP), was performed. Seventy two different herds were restricted for BTB during the FAP; 10 of these herds were restricted twice, resulting in a total of 82 BTB breakdowns. During the first four years of the FAP, the number of BTB herd breakdowns in the area varied from a lowest of nine to a maximum of 18 per year, and were geographically dispersed. In the fifth year of the study a considerable increase in the number of BTB breakdowns (n = 32) was observed, and there was a spatial 'cluster' of infected herds in the eastern part of the study area. The increased number of BTB breakdowns during the fifth year most likely occurred because of the recrudescence of infection, herd-to-herd transmission and, to a lesser extent, purchase of infected cattle. Infected badgers remain as a possible but less likely source of infection, especially as an explanation for the cluster of infected herds. The analysis supports the hypothesis that BTB in herds is a problem that cannot be addressed successfully by dedicating our efforts to the elimination of single risk factors. Neither is it a problem that needs to be investigated only at the herd level, but rather at the area level, including groups of contiguous herds.

Advances in bovine tuberculosis diagnosis and pathogenesis: What policy makers need to know

The mainstay of tuberculosis diagnosis in cattle and deer has been the tuberculin skin test. Recent advances have allowed the incorporation of blood based assays to the diagnostic arsenal for both cattle and deer. Use of defined and specific antigens has allowed for improved specificity of cell mediated assays in both cattle and deer and advances in antibody tests for tuberculosis have potential for use in free-ranging and captive cervid populations. Combined use of blood-based assays with skin testing will require further understanding of the effect of skin testing on the accuracy of blood based assays. Models of experimental infection of cattle have allowed for increased understanding of natural disease pathogenesis. Differences likely exist; however, between cattle and deer in both disease distribution and primary route of inoculation in naturally infected animals.

Pathogenesis of bovine tuberculosis: the role of experimental models of infection

In many countries, test-and-slaughter policies based on tuberculin skin testing have made a significant impact on the control of bovine tuberculosis (caused by infection with Mycobacterium bovis). However, in some countries these policies have not proved as effective and improved disease control strategies are required (including improved diagnostic tests and development of vaccines). The host pathogen interactions in bovine tuberculosis are very complex. While studies of the disease in naturally infected field cases of bovine tuberculosis have provided valuable information, detailed knowledge can also be gained through studies of disease models. A number of studies have developed M. bovis infection models employing a range of routes and challenge doses. An early objective was assessment of vaccine efficiency, and models of infection remain central to current work in this area. Development of the intra-nasal and intra-tracheal models have also advanced our understanding of the kinetics of the immune response. In many of these studies, understanding of pathogenesis has been improved by definition of the cells that respond to infection and those that are instrumental in modulation of host responses. Experimental models of infection have been adapted to study cattle to cattle transmission, modeling one of the fundamental routes of infection. This review provides a historical perspective on the types of experimental models used in over 100 years of research and outlines new opportunities to refine those methods for bovine and human tuberculosis and to contribute to improved diagnostics, advanced understanding of immunology and vaccine design.

Investigation of the transmission of Mycobacterium bovis from deer to cattle through indirect contact

OBJECTIVE

To investigate the infection of calves with Mycobacterium bovis through oral exposure and transmission of M. bovis from experimentally infected white-tailed deer to uninfected cattle through indirect contact.

ANIMALS

24 11-month-old, white-tailed deer and 28 6-month-old, crossbred calves.

PROCEDURE

In the oral exposure experiment, doses of 4.3 x 10(6) CFUs (high dose) or 5 x 10(3) CFUs (low dose) of M. bovis were each administered orally to 4 calves; as positive controls, 2 calves received M. bovis (1.7 x 10(5) CFUs) via tonsillar instillation. Calves were euthanatized and examined 133 days after exposure. Deer-to-cattle transmission was assessed in 2 phases (involving 9 uninfected calves and 12 deer each); deer were inoculated with 4 x 10(5) CFUs (phase I) or 7 x 10(5) CFUs (phase II) of M. Bovis. Calves and deer exchanged pens (phase I; 90 days' duration) or calves received uneaten feed from deer pens (phase II; 140 days' duration) daily. At completion, animals were euthanatized and tissues were collected for bacteriologic culture and histologic examination.

RESULTS

In the low- and high-dose groups, 3 of 4 calves and 1 of 4 calves developed tuberculosis, respectively. In phases I and II, 9 of 9 calves and 4 of 9 calves developed tuberculosis, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that experimentally infected deer can transmit M. bovis to cattle through sharing of feed. In areas where tuberculosis is endemic in free-ranging white-tailed deer, management practices to prevent access of wildlife to feed intended for livestock should be implemented.

Mycobacterium bovis infection, United Kingdom

We describe the first documented spillover of bovine tuberculosis from animals into the human population of the United Kingdom since the resurgence of the disease in cattle in the country. This finding suggests that there may be a small risk for transmission to humans, making continued vigilance particularly necessary.

The transmission of Mycobacterium bovis infection to cattle

The prevalence of Mycobacterium bovis infection in cattle is increasing rapidly in some countries, including the UK and Ireland. The organism infects a wide range of mammalian hosts, and eradication of the disease is difficult if there is an extensive reservoir in the wildlife population. Existing evidence suggests that wildlife vectors include the European badger in the UK and Ireland, the brush-tailed possum and ferret in New Zealand and ungulates in some other countries. Cattle grazing field boundaries or short swards are at particularly high risk, since the chance of contact with the intermediate host or their excreta is increased. There is evidence that the transmission of the disease between cattle following movement accounts for 10-15% of outbreaks in the British Isles and that transmission can occur across farm boundaries. The prevalence the prevalence of single reactors in herds suggested that within-herd transmission was not common. In herds with infected cattle, spreading slurry is a risk factor, which can be minimised by prolonged storage of the slurry, by spreading it on fields not used for grazing or by soil injection. M. bovis also survives in water and may enter the respiratory tract during drinking. It is concluded that M. bovis infection in cattle can be transmitted by a number of routes, some of which can be controlled by appropriate husbandry, but that circumstantial evidence suggests that the existence of a widespread intermediate host is the greatest contributor to infection in cattle.

Mycobacterium bovis infection and tuberculosis in cattle

This review considers the possible events that can occur when cattle are exposed to Mycobacterium bovis and, where appropriate, draws on principles accepted for tuberculosis infection in humans and laboratory animal models. Consideration is given to the many complex factors which influence the outcome of challenge with tubercle bacilli. These include features inherent to the mycobacterium, the host and the environment. It is apparent that clinical disease probably occurs only in a relatively small, but undetermined, proportion of cattle that are exposed to Al. bovis. The majority of animals may clear infection or control the bacilli, possibly in a condition of latency. It is concluded that a better understanding of the dynamics of the events following M. bovis exposure and subsequent infection in cattle would be of significant benefit in developing new tools appropriate for disease control and to designing optimal approaches for their application.

Cattle-to-cattle transmission of Mycobacterium bovis

This review, illustrated with data on the characteristics of herds infected with Mycobacterium bovis (TB) in Great Britain (GB), attempts to identify the role of cattle-to-cattle transmission (CCT) of TB. CCT plays a part in the entry of infection into herds, through purchased infected animals or contiguous spread, although CCT can have a relatively small role in comparison with an established wildlife source. Experimental studies have shown that it is possible for CCT to occur within herds. In 1999, more than one reactor was found in over two-thirds of confirmed TB incidents in Great Britain. The details of transmission from an infectious animal to a susceptible animal are described: proximate, which depends on factors such as closeness of contact and ventilation, or indirect, which also depends on survival outside the host. Herd size is a risk factor for the incidence of TB, both in herds and in individual cattle. Control of TB is considered in relation to the skin test: failure of the test to remove all infected animals from incidents is possible, but probably of less significance than failure to prevent reinfection from sources external to the herd. It is concluded that CCT may have significance in determining the total number of reactors. Safeguarding herds from other sources of TB is likely to reduce CCT as a side effect.

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.

Experimental deer-to-deer transmission of Mycobacterium bovis

OBJECTIVE

To determine whether Mycobacterium bovis can be transmitted from experimentally infected deer to uninfected in-contact deer.

ANIMALS

Twenty-three 6-month-old white-tailed deer.

PROCEDURE

On day 0, M bovis (2 X 10(8) colony-forming units) was administered by intratonsillar instillation to 8 deer; 3 control deer received saline (0.9% NaCl) solution. Eight in-contact deer were comingled with inoculated deer from day 21. On day 120, inoculated deer were euthanatized and necropsied. On day 180, 4 in-contact deer were euthanatized, and 4 new in-contact deer were introduced. On day 360, all in-contact deer were euthanatized. Rectal, oral, and nasal swab specimens and samples of hay, pelleted feed, water, and feces were collected for bacteriologic culture. Tissue specimens were also collected at necropsy for bacteriologic culture and histologic analysis.

RESULTS

On day 90, inoculated and in-contact deer developed delayed-type hypersensitivity (DTH) reactions to purified protein derivative of M bovis. Similarly, new in-contact deer developed DTH reactions by 100 days of contact with original in-contact deer. Tuberculous lesions in in-contact deer were most commonly detected in lungs and tracheobronchial and medial retropharyngeal lymph nodes. Mycobacterium bovis was isolated from nasal secretions and saliva from inoculated and in-contact deer, urine and feces from in-contact deer, and hay and pelleted feed.

CONCLUSIONS AND CLINICAL RELEVANCE

Mycobacterium bovis is efficiently transmitted from experimentally infected deer to uninfected in-contact deer through nasal secretions, saliva, or contaminated feed. Wildlife management practices that result in unnatural gatherings of deer may enhance both direct and indirect transmission of M bovis.

Cattle-to-cattle transmission of bovine tuberculosis

In developed countries, Mycobacterium bovis infection in cattle is now mostly confined to the respiratory system, which reflects transmission and establishment of infection mainly by this route. A single bacillus transported within a droplet nucleus is probably sufficient to establish infection within the bovine lung. Infected cattle should always be considered as potential sources of infection, since studies have demonstrated that a significant proportion of tuberculous cattle excrete M. bovis. In general, the dynamics of M. bovis transmission are poorly understood and the conditions under which a tuberculous animal becomes an effective disseminator of infection are currently not defined although environmental contamination appears to be a less effective method of disease transmission. Field studies indicate a wide spectrum of transmission rates but generally the spread of M. bovis infection is still considered to be a relatively slow process. Slaughter of diseased cattle detected by tuberculin testing and at meat plant inspection has been shown to be an effective policy for tuberculosis eradication, provided there are no other reservoirs of infection and all involved in the cattle industry are committed to a policy of eradication. Epidemiological approaches, particularly case-control studies, seem to provide the best method for quantifying the relative importance of the various sources of M. bovis transmission to cattle and modelling techniques can be used to assist in the design of cost-effective control measures that may lead to tuberculosis eradication.

IgG isotype antibody responses to epitopes of the Mycobacterium bovis protein MPB70 in immunised and in tuberculin skin test-reactor cattle

Serological assays may have merit in identifying animals in advanced stages of bovine tuberculosis, but most tests have had sub-optimal sensitivities and specificities. The Mycobacterium bovis protein MPB70 has been identified as a B-cell target with diagnostic potential in measurement of pre- and post-skin-test antibody responses. One observation, which has potential practical application, has been that skin testing with tuberculin boosts IgG(1) anti-MPB70 antibody responses in cattle with tuberculous lesions. However, serological cross-reactivities with bacteria, such as Nocardia asteroides, have been described for this protein. With the aim of identifying candidate reagents for improved diagnostic tests, this study investigated IgG isotype antibody responses to MPB70 at the epitope level and, because of the previous findings, focused on IgG(1) responses following skin testing. Screening of a panel of overlapping synthetic peptides using sera from cattle immunised with MPB70 and cattle infected with M. bovis showed that two regions of the protein (residues 21-70 and 101-120) contain dominant B-cell epitopes. No individual epitope appeared to be selectively recognised by one isotype of IgG antibody. Investigation of IgG(1) responses showed that recognition of the epitope within residues 51-70 was boosted strongly by tuberculin injections in skin-test positive cattle and that this memory response was generally a feature of cattle which were found to have macroscopic, tuberculous lesions.

Comparison of different methods for diagnosis of bovine tuberculosis from tuberculin- or interferon-gamma-reacting cattle in Spain

Of 1479 cattle from herds in Northwestern Spain previously diagnosed as tuberculosis (TB) positive, 218 animals which gave a positive tuberculin or interferon-gamma reaction were examined at the slaughterhouse. Medial retropharyngeal and caudal mediastinal lymph nodes, and any tissues containing lesions suspected to be tuberculous, were removed and submitted to the laboratory. Three techniques for diagnosis of TB were used: post mortem examination (PME), smear staining by means of auramine O method (AOM), and culture isolation in Coletsos and Lowenstein-Jensen media followed by confirmation of M. tuberculosis complex organisms using PCR (CIM-PCR). Only 123 (29.9%) of the 412 samples collected showed typical tuberculous lesions. Confirmed M. tuberculosis complex organisms were isolated in 144 cases, 114 of which were from tissues showing lesions (success rate of 92.8%). Smears were found positive in 113 cases, 96 of which came from lesions suspected to be tuberculous (success rate of 78.0%). The sensitivities of CIM-PCR compared with those of PME and AOM were 92.7% and 85.7%, respectively. Statistical analysis revealed that PME and AOM are good indicators of the presence of M. tuberculosis complex organisms in tuberculin- or interferon-gamma reacting cattle.

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.

Epidemiology and pathogenesis ofMycobacferium bowisinfection of red deer (Cervus elaphus) in New Zealand

AIMS

This study was initiated to investigate aspects of the epidemiology, pathogenesis and transmission of tuberculosis in wild red deer, with the aim of determining whether this species may be considered a reservoir host of Mycobacterium bovis in New Zealand.

METHOD

One hundred and six wild red deer (Cervus elaphus) carcasses from the Castlepoint and Hauhungaroa Range areas, which are endemic for bovine tuberculosis, were examined for the presence of M. bovis infection. Samples were also examined from 46 skin test-positive farmed deer killed at two deer slaughter premises. Where possible, a standard set of tissues and excretion site samples was collected for mycobacteriological examination.

RESULTS

Fifty-eight infected deer were identified, and of these 28% showed no gross lesions. The prevalence of tuberculosis confirmed by culture in the wild deer was 32%. Only one of 18 deer younger than 1 year was infected. Mature deer (>2 years) were 12 times more likely to be infected than those under 1 year of age. Infected older deer were less likely to show typical gross lesions than younger animals. Mycobacterium bovis was isolated from the oropharyngeal tonsil of 34 of 56 (61%) of the infected deer, and this was the most commonly infected site. Gross lesions were found in 18 of the 34 infected tonsils and only one of these showed a purulent tonsillitis. Mycobacterium bovis was recovered from four of 53 nasopharyngeal tonsils, four of 53 oropharyngeal swabs, one of 53 tracheal and nasal swabs, and one of 46 faecal samples, but not from any urine specimens.

CONCLUSION

These findings suggest that significant bacillary excretion from infected deer was uncommon, and is more likely to occur in severely affected animals. This study has confirmed the importance of mucosa-associated lymphoid tissues (MALT), particularly the oropharyngeal tonsil, in the pathogenesis of tuberculosis in deer. The findings justify investigation of the hypotheses that the prevalence of tuberculosis in wild deer in New Zealand is high due to transmission of infection from possums, and that in the absence of an infected possum population, the prevalence of tuberculosis in deer is likely to be low, and spatially patchy.

CLINICAL RELEVANCE

The results suggest that about one quarter of infected deer show no detectable gross lesions. This implies that many infected carcasses may enter the food chain unrecognised and that the estimated sensitivity and specificity of diagnostic tests may be erroneous if there is a difference in test performance between those conducted on deer with or without gross lesions. Diagnostic sensitivity following slaughter may be improved by routine culture of oropharyngeal tonsils and careful examination of lungs for adhesions and small subpleural tubercles.

Mycobacterial antigen-specific antibody responses in bovine tuberculosis: an ELISA with potential to confirm disease status

Serological assays may help to identify animals in advanced stages of bovine tuberculosis, but most of the tests available have suboptimal sensitivities and specificities. This study was designed to determine whether the antibody responses to defined antigens (rMPB70, rMPB64 and rMPB59) of Mycobacterium bovis at the immunoglobulin subclass level could be used to develop improved serological tests. In experimentally infected cattle it was found that the predominant serum antibody response was to rMPB70, and that an IgG1 response to this antigen was boosted strongly by skin testing. Studies in naturally infected cattle suggested that this memory IgG1 anti-rMPB70 response may be able to differentiate between skin test-reactor animals with and without lesions by comparing the ratio of the antibody response before and after skin testing. The study has provided a clearer understanding of the kinetics of antibody responses to defined mycobacterial antigens at the subclass level in bovine tuberculosis and has made it possible to develop a novel ELISA system which may be useful in disease diagnosis.

Performance of the single intradermal comparative tuberculin test in identifying cattle with tuberculous lesions in Irish herds

The sensitivity of the single intradermal comparative tuberculin test, as applied in the Republic of Ireland, was estimated in 353 cattle with tuberculous lesions. These cattle had been removed from 47 herds which were depopulated owing to chronic or extensive infection with Mycobacterium bovis. The test had a sensitivity of 90.9 per cent, because 321 (90.9 per cent) of the 353 cattle with tuberculous lesions gave a positive or inconclusive result, and 32 gave a negative result. These 32 negative cattle came from 17 (36 per cent) of the 47 depopulated herds.

A study of the environmental survival ofMycobacterium bovison a farm in New Zealand

Mycobacterium bovis organisms absorbed on cotton ribbons were placed in different natural habitats on a farm in New Zealand. Mycobacterium bovis was not re-isolated from ribbons placed on pasture after 4 days. Survival on ribbons was longest in brushtail possum dens, where the maximum period of survival in dens was less than 7 days in summer and greater than 14 days but less than 28 days in winter and spring. The maximum period of survival on a forest floor was intermediate between pasture and dens less than 4 days in summer and greater than 14 days but less than 28 days in winter. The overall probability of survival was influenced by season and was shortest in summer and longest in spring and winter. Survival time increased as minimum daily temperatures decreased. These studies showed there was a relatively short period of survival of M. bovis outside hosts and support a conclusion that environmental contamination of pasture, particularly in summer months, may be relatively unimportant in the epidemiology of tuberculosis in cattle, deer and possums.

The epidemiology of Mycobacterium bovis infections in animals and man: a review

Tuberculosis is primarily a respiratory disease and transmission of infection within and between species is mainly by the airborne route. Mycobacterium bovis, the cause of bovine-type tuberculosis, has an exceptionally wide host range. Susceptible species include cattle, humans, non-human primates, goats, cats dogs, pigs, buffalo, badgers, possums, deer and bison. Many susceptible species, including man, are spillover hosts in which infection is not self-maintaining. In countries where there is transmission of infection from endemically infected wildlife populations to cattle or other farmed animals, eradication is not feasible and control measures must be applied indefinitely. Possible methods of limiting spread of infection from wildlife to cattle including the use of vaccines are outlined. The usefulness of DNA fingerprinting of M. bovis strains as an epidemiological tool and of BCG vaccination of humans and cattle as a control measure are reviewed. The factors determining susceptibility to infection and clinical disease, and the infectiousness of infected hosts and transmission of infection, are detailed. Reports of the epidemiology of M. bovis infections in man and a variety of animal species are reviewed. M. bovis infection was recognised as a major public health problem when this organism was transmitted to man via milk from infected cows. The introduction of pasteurization helped eliminate this problem. Those occupational groups working with M. bovis infected cattle or deer, on the farm or in the slaughter house, are more likely to develop pulmonary disease than alimentary disease. In recent years, tuberculosis in farmed cervidae has become a disease of economic as well as public health importance in several countries. Nowadays, the human immunodeficiency virus (HIV) is associated with a greatly increased risk of overt disease in humans infected with Myobacterium tuberculosis. It is believed this increased risk also occurs in the case of M. bovis infections in humans.

The epidemiology of Mycobacterium bovis infections

Mycobacterium bovis has an exceptionally wide host range, but until recent years there was little concern about infection in species other than cattle and man. Diversification of farming enterprises has led to cognizance of the need for control in other domestic animals, notably deer. There has also been recognition that self-maintaining infection is present in wildlife hosts in some countries--notably the European badger in the United Kingdom and Ireland, the Australian brush-tailed possum in New Zealand, and various species of ungulates in limited areas of a number of countries. Although transmission of M. bovis can occur by a number of different routes, control measures imposed on cattle and to a lesser extent on other species have reduced a number of the routes to insignificance. Hence the vast preponderance of transmission within host species is now by the airborne route, and predominantly between species as well. Transmission of infection from badgers to cattle may be an exception, with evidence remaining equivocal about the relative importance of pasture contamination by excretion in badger urine and airborne transmission. In general, contamination of feed and pasture appears to be unimportant in transmission of the disease, because survival times of infective doses of organisms on fomites are relatively short under realistic conditions and because animals are not commonly exposed to a dose high enough to be infective by the alimentary route. Infection through the oro-pharyngeal mucous membrane may be significant, although the infective dose for this route is not known. While many species of animals can become infected with M. bovis, only a few act as maintenance hosts and the rest are spillover hosts in which infection is not self-maintaining. With the exception of cattle and deer, other species have become maintenance hosts only within part of their ecological range. For both badgers and possums, maintenance of infection within a local population is due to pseudo-vertical transmission from mother to young, and horizontal transmission linked to breeding activity. Transmission from possums to domestic animals appears to occur mainly during atypical behavioural interactions between the species, and this may well be important for badgers as well. Difficulties in controlling the disease adequately in domestic animals generally result from administrative problems since the necessary technical procedures are available and have been shown to be effective. Where there is interplay between infection in wildlife and domestic animals, eradication of the disease becomes impractical.(ABSTRACT TRUNCATED AT 400 WORDS)

Pathogenesis of Mycobacterium bovis infection in cattle

This paper reviews the pathogenesis of Mycobacterium bovis infection in cattle, focusing on aspects relating to the host rather than the organism. A broad concept of pathogenesis has been considered and information is presented on sources and routes of infection, as well as the immune responses and pathology. In addition, data is presented on the excretion of M. bovis from tuberculous cattle.

Responses of dairy cows to badger urine and faeces on pasture with reference to bovine tuberculosis transmission

Grazing cattle were observed when they encountered badger urine or faeces which, in all but the first study, came only from badgers which were not infected with bovine tuberculosis. The faeces were very strongly avoided and there was generally a strong avoidance of ingestion of badger urine. There was no evidence that cattle were attracted to badger latrines in an area where some infected badgers were present and cows actively avoided faeces up to 28 days old which was placed on grass turves or on pasture. 99.3% of cows took no bites from small grass plots contaminated with faeces and 88.7% of cows took no bites from urine-treated plots. There was generally avoidance of pasture treated with badger urine up to 14 days old. However, two cows out of 240 were willing to graze close to faeces and seven out of 240 were willing to graze near urine. Contaminated herbage was eaten most when attractive herbage became scarce. Wet weather did not reduce the strength of avoidance of urine. Some cows responded to badger urine, and to a lesser extent to faeces, by more sniffing, particularly when herbage was scarce. The odour of faeces, and sometimes that of urine, often resulted in the ejection of mouth contents. As a consequence of their avoidance of badger faeces and urine, the vast majority of cows are unlikely to contract tuberculosis from infected badgers by ingestion. Most cows totally avoid badger products so they are unlikely to be infected via inhalation. However, the small minority of unselective cows must be more at risk and this finding warrants further investigation.

A mathematical model for Mycobacterium bovis excretion from tuberculous cattle

An analysis was carried out of available information from a series of experiments on the excretion of M. bovis from infected cattle. The analysis indicated that an inverse exponential relationship exists between 'dose' of organisms given and the delay before excretion commences. This relationship was represented mathematically. Available field data supported the relationship and indicated that in natural bovine tuberculosis excretion of M. bovis begins around 87 days after infection occurs. It is also suggested that the data supports the concept of single nuclei infections in cattle.