Infected Badgers Research Articles

Evaluation of a method to detect Mycobacterium bovis in air samples from infected Eurasian badgers (Meles meles ) and their setts

Environmental air sampling was evaluated as a method to detect the presence of M.bovis in the vicinity of infected badgers and their setts. Airborne particles were collected on gelatine filters using a commercially available air sampling instrument and tested for the presence of M.bovis using bacteriological culture and real-time PCR. The sensitivity of bacteriological culture was broadly similar to that of real-time PCR when testing samples artificially spiked with M.bovis. Sampling was undertaken from directly under the muzzles of badgers which had been experimentally infected with M.bovis (37 samples), within enclosures housing the experimentally infected animals (50 samples), and in the vicinity of setts with resident infected wild badgers (52 samples). The methods employed did not detect M.bovis from either infected badgers or artificial or natural setts known to contain infected animals. However, samples taken at four of the six natural setts were positive for Mycobacterium gordonae.

Direction of Association between Bite Wounds and Mycobacterium bovis Infection in Badgers: Implications for Transmission

BackgroundBadgers are involved in the transmission to cattle of bovine tuberculosis (TB), a serious problem for the UK farming industry. Cross-sectional studies have shown an association between bite wounds and TB infection in badgers which may have implications for M. bovis transmission and control, although the sequence of these two events is unclear. Transmission during aggressive encounters could potentially reduce the effectiveness of policies which increase the average range of a badger and thus its opportunities for interaction with other social groups.MethodsData were obtained on badgers captured during a long term study at Woodchester Park, UK (1998–2006). Many badgers had multiple observations. At each observation, the badger was assigned a “state” depending on presence of bite wounds and/or TB infection. Hence each badger had a “transition” from the previous state to the current state. We calculated the numbers of each type of transition and the time spent in each state. Transition rates were calculated for each transition category, dividing the number of such transitions by the total time at risk. We compared the rate of bite wound acquisition in infected badgers with that for uninfected badgers and the rate of positive M.bovis test results in bitten badgers with that in unbitten badgers.ResultsThe rate of bite wound acquisition in infected badgers (0.291 per year) was 2.09 (95% CI: 1.41, 3.08) times that in uninfected badgers (0.139 per year). The rate of positive M.bovis test results in bitten badgers (0.097 per year) was 2.45 (95% CI: 1.29, 4.65) times that in unbitten badgers (0.040 per year).ConclusionsWe found strong evidence of both potential sequences of events consistent with transmission via bite wounds and distinctive behaviour in infected badgers. The complex relationship between behaviour and infection must be considered when planning TB control strategies.

A forensic investigation of Mycobacterium bovis infection in badgers

A forensic investigation of Mycobacterium bovis infection in badgers

The distribution of Mycobacterium bovis infection in naturally infected badgers

Populations of Eurasian badgers (Meles meles) with tuberculosis (Mycobacterium bovis infection) are a significant reservoir of infection for cattle in Ireland and the United Kingdom. In this study the distribution of infection, histological lesions and gross lesions was determined in a sample of 132 culled badgers from naturally-infected wild populations. Badgers were culled when an epidemiological investigation following a tuberculosis breakdown in a cattle herd implicated badgers as the probable source of infection. The definition of tuberculosis infection was based on the isolation of M. bovis from tissues or clinical samples. An accurate diagnosis of infection was achieved by culturing a wide range of lymph nodes (LN) and organ tissues (mean 32.1) and clinical samples (faeces and urine) from each badger. Infection was detected in 57/132 badgers (43.2%). Histological lesions consistent with tuberculosis were seen in 39/57 (68.4%) culture-positive and 7/75 (9.3%) culture-negative animals. Gross lesions were seen in only 30/57 (52.6%) infected badgers, leaving a high proportion (47.4%) of infected animals with latent infection (no grossly visible lesions). The most frequently infected tissues were the lungs and axillary LN, followed by the deep cervical LN, parotid LN and tracheobronchial LN. The data support the hypotheses that in badgers there are only two significant routes of infection, namely, the lower respiratory tract and bite wounds, and that badgers are very susceptible to infection but resistant to the development and progression of the disease. At all levels of disease severity, infection was found in widely dispersed anatomical locations suggesting that there is early dissemination of infection in the period preceding the development of active immunity.

Geographical association between the genotype of bovine tuberculosis in found dead badgers and in cattle herds

In a survey, 457 badgers that had been found dead in Wales were postmortem-examined, and samples were examined by histology and by extended culture (for up to 12 weeks). Mycobacterium...

Evaluating selective culling with vaccination to control wildlife disease: badgers and bovine tuberculosis (bTB)

Emerging infectious diseases often originate in wildlife, but the complex dynamics of wild animal populations mean that disease control is a major scientific and policy challenge. Culling and vaccination can be effective but the ecological characteristics of wild animals may confound the outcomes of simple management programs. In Britain, badgers Meles meles are a recognized reservoir of Mycobacterium bovis, the causative agent of bovine tuberculosis (bTB), and are involved in its transmission to cattle. Experiments have shown that culling badgers can increase bTB incidence in badgers and cattle, by perturbing the social structure of badger populations, and increasing contact rates. Selectively removal of infected badgers and vaccination of the remainder has recently been advocated as a potential solution. Simulation modelling suggests that this intuitively appealing policy could at best deliver only a minor advantage over thoroughly applying either vaccination or culling, but carries a risk of making the disease problem much worse. We suggest this counterintuitive outcome arises because: 1, not all animals can be caught and tested 2, some genuinely infected animals will be test negative 3, selective culling leaves a larger population of susceptible hosts than non-selective culling 4, some susceptible hosts will not respond to vaccination and 5, perturbation increases contact and transmission rates among a relatively high density population of infectious and susceptible animals.

Protection of Eurasian badgers ( Meles meles) from tuberculosis after intra-muscular vaccination with different doses of BCG

Mycobacterium bovis infection is widespread in Eurasian badger ( Meles meles) populations in Great Britain and the Republic of Ireland where they act as a wildlife reservoir of infection for cattle. Removal of infected badgers can significantly reduce the incidence of bovine tuberculosis (TB) in local cattle herds. However, control measures based on culling of native wildlife are contentious and may even be detrimental to disease control. Vaccinating badgers with bacillus Calmette-Guerin (BCG) has been shown to be efficacious against experimentally induced TB of badgers when administered subcutaneously and orally. Vaccination may be an alternative or complementary strategy to other disease control measures. As the subcutaneous route is impractical for vaccinating wild badgers and an oral vaccine bait formulation is currently unavailable, we evaluated the intramuscular (IM) route of BCG administration. It has been demonstrated that the IM route is safe in badgers. IM administration has the practical advantage of being relatively easy to perform on trapped wild badgers without recourse to chemical immobilisation. We report the evaluation of the efficacy of IM administration of BCG Danish strain 1331 at two different doses: the dose prescribed for adult humans (2–8 × 10 5 colony forming units) and a 10-fold higher dose. Vaccination generated a dose-dependent cell-mediated immune response characterised by the production of interferon-γ (IFNγ) and protection against endobronchial challenge with virulent M. bovis. Protection, expressed in terms of a significant reduction in the severity of disease, the number of tissues containing acid-fast bacilli, and reduced bacterial excretion was statistically significant with the higher dose only.

Tuberculosis in cattle herds are sentinels for Mycobacterium bovis infection in European badgers ( Meles meles): The Irish Greenfield Study

In Ireland badgers are removed in response to tuberculosis (TB) breakdowns in cattle herds (focal culling). Prevalence studies, conducted using a detailed post mortem and bacteriological examination, showed that 36–50% of badgers were infected with Mycobacterium bovis. Focal culling forms part of the medium term national strategy for the control of bovine TB in cattle and is based on the premise that badgers in areas with herd breakdowns have a higher prevalence of infection than the badger population at large. However, the hypothesis that cattle can be used as sentinels for infection in the badger population has never been formally tested. In this study we tested the hypothesis by determining the infection prevalence in badgers in areas where there had been historically, a consistently low prevalence of infection in cattle. Low cattle TB prevalence areas were defined as those herds with ≤2 standard reactors in the annual round of skin testing over the preceding 5 years (Greenfield sites). Using GIS, and adjusting for variation in land use, previous culling and cattle density, 198 Greenfield sites were identified and surveyed, and 138 areas with badger setts or signs of badger activity were identified. A single badger was removed from 87 sites and all were examined using detailed post mortem and bacteriological procedures. A prevalence of M. bovis infection of 14.9% was found in the Greenfield site badgers. This prevalence was significantly lower ( P < 0.001) than in badgers removed during focal culling (36.6%). The results validate the use of cattle as sentinels for TB in badgers and support the medium term national strategy for the control of bovine TB. The geographic variation in M. bovis infection prevalence in the Irish badger populations will be used when devising strategies for the incorporation of badger vaccination into the long term bovine TB control programme.

Infection of Eurasian badgers (Meles meles) with Mycobacterium avium complex (MAC) bacteria

There are few reports of infection with Mycobacterium avium complex (MAC) bacteria in badgers. In this study archive data relating to the isolation of MAC organisms from badgers in the UK is presented, and information derived from recent cases of such infection in Spain is used to illustrate the associated pathology and to characterise strain types. Tissue samples were cultured for mycobacteria and, in the case of Spanish badgers, were examined both histopathologically and using immunohistochemistry, and DNA typing of M. avium isolates was also carried out. A total of 5 (7.35%) and 281 (0.51%) isolates of M. avium spp. were recovered from badgers from the studies in Spain and the UK, respectively. DNA typing of the isolates from Spain identified the sub-species M. avium hominissuis and M. avium avium. These findings provide new information on the prevalence of MAC organisms in badgers in the UK and Spain. The extent to which infected badgers may be involved in the epidemiology of M. avium in other wild or domestic hosts remains unknown.

Estimating the extent of spatial association ofMycobacterium bovisinfection in badgers in Ireland

Mycobacterium bovis infects the wildlife species badgers Meles meles who are linked with the spread of the associated disease tuberculosis (TB) in cattle. Control of livestock infections depends in part on the spatial and social structure of the wildlife host. Here we describe spatial association of M. bovis infection in a badger population using data from the first year of the Four Area Project in Ireland. Using second-order intensity functions, we show there is strong evidence of clustering of TB cases in each the four areas, i.e. a global tendency for infected cases to occur near other infected cases. Using estimated intensity functions, we identify locations where particular strains of TB cluster. Generalized linear geostatistical models are used to assess the practical range at which spatial correlation occurs and is found to exceed 6 in all areas. The study is of relevance concerning the scale of localized badger culling in the control of the disease in cattle.

The prevalence and distribution of Mycobacterium bovis infection in European badgers ( Meles meles) as determined by enhanced post mortem examination and bacteriological culture

The accurate diagnosis of Mycobacterium bovis infection in badgers is key to understanding the epidemiology of tuberculosis in this species and has significant implications for devising strategies to limit spread of the disease. In this study, badgers ( n = 215) in the Republic of Ireland were examined at post mortem and tissues were collected from a range of anatomical locations and pooled into groups for bacterial culture of M. bovis. By assessing confirmed gross visible lesions (VL) alone, infection was detected in 12.1% of badgers. However, by including the results of all culture positive pooled samples, the overall infection prevalence increased significantly to 36.3%. Two-thirds (66.7%) of infected animals had no visible lesions (NVL). While the thoracic cavity (lungs and pulmonary lymph nodes) was found to be the most common site of infection, in a proportion of animals infection was absent from the lungs and draining lymph nodes and was confined to the lymph nodes of the carcase or the head. This may indicate an early extrapulmonary dissemination of infection or alternatively, in the case of the head lymph nodes, a secondary pathogenic pathway involving the lymphoid tissues of the upper respiratory tract (URT).

Social group size affects Mycobacterium bovis infection in European badgers (Meles meles)

1. In most social animals, the prevalence of directly transmitted pathogens increases in larger groups and at higher population densities. Such patterns are predicted by models of Mycobacterium bovis infection in European badgers (Meles meles). 2. We investigated the relationship between badger abundance and M. bovis prevalence, using data on 2696 adult badgers in 10 populations sampled at the start of the Randomized Badger Culling Trial. 3. M. bovis prevalence was consistently higher at low badger densities and in small social groups. M. bovis prevalence was also higher among badgers whose genetic profiles suggested that they had immigrated into their assigned social groups. 4. The association between high M. bovis prevalence and small badger group size appeared not to have been caused by previous small-scale culling in study areas, which had been suspended, on average, 5 years before the start of the current study. 5. The observed pattern of prevalence might occur through badgers in smaller groups interacting more frequently with members of neighbouring groups; detailed behavioural data are needed to test this hypothesis. Likewise, longitudinal data are needed to determine whether the size of infected groups might be suppressed by disease-related mortality. 6. Although M. bovis prevalence was lower at high population densities, the absolute number of infected badgers was higher. However, this does not necessarily mean that the risk of M. bovis transmission to cattle is highest at high badger densities, since transmission risk depends on badger behaviour as well as on badger density.

BOVINE TUBERCULOSIS IN CATTLE AND BADGERS IN LOCALIZED CULLING AREAS

Bovine tuberculosis (TB) is a zoonotic disease that can have serious consequences for cattle farming and, potentially, for public health. In Britain, failure to control bovine TB has been linked to persistent infection of European badger (Meles meles) populations. However, culling of badgers in the vicinity of recent TB outbreaks in cattle has failed to reduce the overall incidence of cattle TB. Using data from a large-scale study conducted in 1998-2005, we show that badgers collected on such localized culls had elevated prevalence of Mycobacterium bovis, the causative agent of bovine TB, suggesting that infections in cattle and badgers were indeed associated. Moreover, there was a high degree of similarity in the M. bovis strain types isolated from cattle and associated badgers. This similarity between strain types appeared to be unaffected by time lags between the detection of infection in cattle and culling of badgers, or by the presence of purchased cattle that might have acquired infection elsewhere. However, localized culling appeared to prompt an increase in the prevalence of M. bovis infection in badgers, probably by disrupting ranging and territorial behavior and hence increasing intraspecific transmission rates. This elevated prevalence among badgers could offset the benefits, for cattle, of reduced badger densities and may help to explain the failure of localized culling to reduce cattle TB incidence.

Vaccination of European badgers ( Meles meles) with BCG by the subcutaneous and mucosal routes induces protective immunity against endobronchial challenge with Mycobacterium bovis

Mycobacterium bovis is endemic in badger (Meles meles) populations of Ireland and the United Kingdom and infected badgers are a potential source of infection for cattle. In domestic livestock tuberculosis causes economic losses from lost production and the costs associated with eradication programmes, and in addition there is a risk of zoonotic infection. Whereas culling is currently used to control tuberculous badger populations in Ireland, vaccination, if it were available, would be preferred. A study was undertaken to examine the protective responses of badgers vaccinated either by the subcutaneous or mucosal (intranasal and conjunctival) routes with bacille Calmette-Guérin (BCG), when challenged with M. bovis by the endobronchial route. Three groups of badgers were used. The first group (n=4) was vaccinated with approximately 5 x 10(5) colony forming units (cfu) of BCG by subcutaneous injection. In the second group (n=5) badgers were vaccinated via the mucosal route by instilling 1.0 x 10(5)cfu into each conjunctival sac and spraying 1.0 x 10(5)cfu into each nostril (final vaccine dose of 4 x 10(5)cfu). The control (n=5) badgers served as a non-vaccinated group. Twelve weeks post-vaccination all badgers in the three groups were challenged with approximately 10(4)cfu of M. bovis by endobronchial inoculation. At 12 weeks post-infection all badgers were examined post-mortem to assess the pathological and bacteriological responses to challenge. Gross and histological lesions of tuberculosis were seen in all challenged badgers and M. bovis was recovered from all challenged badgers. However, across six of the eight parameters used to measure disease severity, the infection in the vaccinated badgers was significantly less severe than in the control group. The BCG vaccine induced a significant protective effect in the badgers and the protective immunity was generated by subcutaneous and mucosal vaccination.

Experimental tuberculosis in the European badger ( Meles meles) after endobronchial inoculation with Mycobacterium bovis: II. Progression of infection

The aim of the study was to describe, over a period of 24 weeks, the pathological and bacteriological changes in badgers experimentally infected with Mycobacterium bovis. The badgers were infected by endobronchial instillation of 2.5 × 10 4 colony forming units (cfu) M. bovis. After infection, the badgers were examined at 3 weekly intervals when blood and tracheal aspirates were collected. At 6, 12, 18 and 24 weeks post-infection (pi) three animals were euthanized and a detailed pathological and bacteriological examination was performed to assess the nature of the experimental disease. During the course of the study only one badger developed clinical signs of disease: a subcutaneous swelling on its head, first observed at 18 weeks pi. At post-mortem examination gross and histological lesions of tuberculosis were observed and M. bovis was recovered from all, except one badger. In the majority of badgers the endobronchial route of inoculation resulted in the establishment of infection that over 24 weeks was non-progressive with limited dissemination of infection from the thoracic cavity, mainly to the hepatic and mesenteric lymph nodes. However, in one of the badgers examined at 18 weeks pi and one at 24 weeks pi, infection was widely disseminated. The disease induced by the endobronchial inoculation displayed the characteristics of disease observed in naturally infected badgers.

The effect of varying levels of population control on the prevalence of tuberculosis in badgers in Ireland

We examined the effect of varying levels of badger population control on the prevalence of Mycobacterium bovis infection in badgers in four counties of Ireland. In the ‘Removal’ and ‘Buffer’ areas, proactive culling was conducted to substantially reduce and subsequently maintain badger populations at a low level for five years. In the ‘Reference’ areas, localised reactive culling was conducted in association with herd breakdowns. The infection status of badgers was determined using bacteriology. A total of 2696 badgers were recruited into the study, and 19.0% were found to be infected with M. bovis. The two population control strategies had differing effects on the subsequent prevalence of tuberculosis in badger populations. Proactive culling led to a long term decrease in the prevalence of tuberculosis in the re-emergent populations. Although there was an overall decline in the disease prevalence, no consistent trend in disease prevalence as a result of reactive culling was observed.

Antigen specific immunological responses of badgers ( Meles meles) experimentally infected with Mycobacterium bovis

European badgers ( Meles meles) are considered to be an important reservoir of infection for Mycobacterium bovis and are implicated in the transmission of tuberculosis to cattle in Ireland and Great Britain. Accurate tests are required for tuberculosis surveillance in badger populations and to provide a basis for the development of strategies, including vaccination, to reduce the incidence of the infection. In this study, we have developed an endobronchial M. bovis infection model in badgers in which we measured cell-mediated immune and serological responses for up to 24 weeks post-infection. Groups of badgers were subjected to necropsy at 6-week intervals and the gross lesion severity status compared with immune responses measured in blood samples taken throughout the course of the study. The panel of antigens included bovine and avian tuberculins (PPD) as well as single antigens, ESAT-6, CFP-10, MPB70, Rv3019c, Rv3873, Rv3878 and Rv3879, all known to be recognised by the immune system in other animal models of tuberculosis infection. Our results demonstrated that M. bovis infected badgers responded to specific antigens as early as 6 weeks post-infection, consistent with the presence of visible lesions. The data also revealed unique patterns of antigen recognition with high levels of PBMC proliferation in the presence of CFP-10 but low proliferation levels with ESAT-6. Using a multi-antigen print immunoassay (MAPIA), we were able to confirm that MPB83 is the dominant antigen recognised by serum antibodies in infected badgers.

Genetic evidence that culling increases badger movement: implications for the spread of bovine tuberculosis

The Eurasian badger (Meles meles) has been implicated in the transmission of bovine tuberculosis (TB, caused by Mycobacterium bovis) to cattle. However, evidence suggests that attempts to reduce the spread of TB among cattle in Britain by culling badgers have mixed effects. A large-scale field experiment (the randomized badger culling trial, RBCT) showed that widespread proactive badger culling reduced the incidence of TB in cattle within culled areas but that TB incidence increased in adjoining areas. Additionally, localized reactive badger culling increased the incidence of TB in cattle. It has been suggested that culling-induced perturbation of badger social structure may increase individual movements and elevate the risk of disease transmission between badgers and cattle. Field studies support this hypothesis, by demonstrating increases in badger group ranges and the prevalence of TB infection in badgers following culling. However, more evidence on the effect of culling on badger movements is needed in order to predict the epidemiological consequences of this control strategy. Here, analysis of the genetic signatures of badger populations in the RBCT revealed increased dispersal following culling. While standard tests provided evidence for greater dispersal after culling, a novel method indicated that this was due to medium- and long-distance dispersal, in addition to previously reported increases in home-range size. Our results also indicated that, on average, badgers infected with M. bovis moved significantly farther than did uninfected badgers. A disease control strategy that included culling would need to take account of the potentially negative epidemiological consequences of increased badger dispersal.

Environmental monitoring of Mycobacterium bovis in badger feces and badger sett soil by real-time PCR, as confirmed by immunofluorescence, immunocapture, and cultivation.

Real-time PCR was used to detect and quantify Mycobacterium bovis cells in naturally infected soil and badger feces. Immunomagnetic capture, immunofluorescence, and selective culture confirmed species identification and cell viability. These techniques will prove useful for monitoring M. bovis in the environment and for elucidating transmission routes between wildlife and cattle.

Experimental tuberculosis in the European badger ( Meles meles) after endobronchial inoculation of Mycobacterium bovis: I. Pathology and bacteriology

The aim was to develop an endobronchial infection procedure for the study of Mycobacterium bovis infection in badgers. The badgers were anaesthetised and a cannula was passed per os to the tracheal bifurcation. When in place 1 ml of M. bovis suspension was inoculated. Three concentrations of M. bovis suspension were used; <10 colony forming units (cfu), ∼10 2 cfu and ∼3 × 10 3 cfu. The badgers were examined at three weekly intervals for clinical signs of disease and a tracheal aspirate was collected at each examination. The badgers were euthanased 17 weeks post infection (pi) and at the post mortem examination a wide range of tissues were examined for gross and histopathological lesions of tuberculosis and cultured for M. bovis. A sample of bronchial alveolar lavage (BAL) fluid was collected at post mortem for culture. At post mortem examination 17 weeks after infection, gross and histopathological lesions of tuberculosis were observed in all badgers inoculated with the high and medium dose and 1/3 inoculated with the low dose. M. bovis was recovered from all inoculated badgers. Infection in the high dose group was more widely disseminated than in the other groups. The number of sites with gross and histopathological lesions increased with increasing dose of M. bovis. All tracheal aspirates were negative on culture and only one BAL, collected from a badger of the high dose group, was positive on culture. No clinical signs due to the experimental infection were observed. The endobronchial route of inoculation is an effective route for establishing experimental infection, and could be used for studies of tuberculosis pathogenesis, immunology of M. bovis infection in badgers and for challenging badgers in vaccine protection studies. Badgers appeared to be very susceptible to infection by this procedure even with a dose of <10 cfu but appear to control and limit the resulting infection.