Assessing effects from four years of industry-led badger culling in England on the incidence of bovine tuberculosis in cattle, 2013-2017

An extensive re-evaluation of evidence and analyses of the Randomised Badger Culling Trial (RBCT) I: Within proactive culling areas

Here, in the first of two investigations, we evaluate and extend the analyses of the Randomised Badger Culling Trial (RBCT) to estimate the effectiveness of proactive badger culling for reducing incidence of tuberculosis (TB) in cattle within culling areas. Using previously reviewed, publicly available data, alongside frequentist and Bayesian approaches, we re-estimate culling effects for confirmed incidence of herd breakdowns (TB incidents in cattle) within proactive culling areas. We appraise the varying assumptions and statistical structures of individual models to determine model appropriateness. Our re-evaluation of frequentist models provides results consistent with peer-reviewed analyses of RBCT data, due to the consistency of beneficial effects across three analysis periods. Furthermore, well-fitting Bayesian models with weakly informative prior distribution assumptions produce high probabilities (91.2%-99.5%) of beneficial effects of proactive culling on confirmed herd breakdowns within culling areas in the period from the initial culls (between 1998 and 2002) until 2005. Similarly high probabilities of beneficial effects were observed post-trial (from 1 year after last culls until March 2013). Thus, irrespective of statistical approach or study period, we estimate substantial beneficial effects of proactive culling within culling areas, consistent with separate, existing, peer-reviewed analyses of the RBCT data.

Absence of effects of widespread badger culling on tuberculosis in cattle

Government policy in England aims for the elimination of bovine tuberculosis (bTB). This policy includes culling of European badger (Meles meles) to reduce cattle TB incidence. The rationale is based on a field trial, the Randomised Badger Culling Trial (RBCT) 1998-2005, which reported a substantial decrease in bTB herd incidence where badger culling had been implemented, in comparison to untreated control areas. The RBCT was undertaken because previous studies of reductions in badgers by culling, reported a possible association between bTB in badger and cattle, but none could directly show causation. The effect of intensive widespread (proactive) culling in the RBCT was reported in 2006 in the journal Nature. Analysis of an extensive badger removal programme in England since 2013 has raised concerns that culling has not reduced bTB herd incidence. The present study re-examined RBCT data using a range of statistical models. Most analytical options showed no evidence to support an effect of badger culling on bTB herd incidence 'confirmed' by visible lesions and/or bacterial culture post mortem following a comparative intradermal skin test (SICCT). However, the statistical model chosen by the RBCT study was one of the few models that showed an effect. Various criteria suggest that this was not an optimal model, compared to other analytical options available. The most likely explanation is that the RBCT proactive cull analysis over-fitted the data with a non-standard method to control for exposure giving it a poor predictive value. Fresh appraisal shows that there was insufficient evidence to conclude RBCT proactive badger culling affected bTB breakdown incidence. The RBCT found no evidence of an effect of culling on 'total' herd incidence rates. Total herd incidences include those confirmed as bTB at necropsy and those herds where there was at least one animal animal positive to the comparative intradermal skin test, the standard diagnostic test used for routine surveillance, but not confirmed at necropsy. This was also the case using the more suitable statistical models. Use only of 'confirmed' herd incidence data, together with a more recent (2013) published perception that RBCT data presented 'a strong evidence base….with appropriate detailed statistical or other quantitative analysis' should be reconsidered. The results of the present report are consistent with other analyses that were unable to detect any disease control benefits from badger culling in England (2013-2019). This study demonstrates one form of potential driver to the reproducibility crisis, in this case with disease control management in an increasingly intensified livestock industry.

Is badger culling associated with risk compensation behaviour among cattle farmers?

BACKGROUND

Risk compensation theory suggests that behaviours are modified in response to interventions that remove risks by substituting them with other risky behaviours to maintain a 'risk equilibrium'. Alternatively, risk reduction interventions may result in spill-over behaviours that seek to minimise risks further. This paper assessed evidence for these behavioural risk responses among farmers in response to badger culling that seeks to remove the risk of bovine tuberculosis in cattle.

METHODS

Data from the UK's randomised badger culling trial were re-analysed, comparing farmers' cattle movement practices in proactive and reactive culling areas and control areas. Analysis compared cattle movements during and after the trial using zero-inflated negative binomial regression.

RESULTS

The analysis found no strong evidence of risk compensation behaviours among farmers who experienced proactive culling. However, strong evidence for a reduction in cattle movements in reactive culling areas was found. The results indicate high levels of inertia within farming systems in relation to cattle purchasing.

LIMITATIONS

Data do not account for the risk of cattle purchases and reflect previous policy regimens. Evidence from recent badger culling interventions should be analysed.

CONCLUSION

Proactive badger culling was not associated with risk compensation behaviours, while reactive badger culling was associated with decreased risk taking among farmers.

Use of an expert elicitation methodology to compare welfare impacts of two approaches for blood sampling European badgers (Meles meles) in the field

In the UK and Republic of Ireland, the European badger (Meles meles) is considered the most significant wildlife reservoir of the bacterium Mycobacterium bovis, the cause of bovine tuberculosis (bTB). To expand options for bTB surveillance and disease control, the Animal and Plant Health Agency developed a bespoke physical restraint cage to facilitate collection of a small blood sample from a restrained, conscious badger in the field. A key step, prior to pursuing operational deployment of the novel restraint cage, was an assessment of the relative welfare impacts of the approach. We used an established welfare assessment model to elicit expert opinion during two workshops to compare the impacts of the restraint cage approach with the only current alternative for obtaining blood samples from badgers in the field, which involves administration of a general anaesthetic. Eleven panellists participated in the workshops, comprising experts in the fields of wildlife biology, animal welfare science, badger capture and sampling, and veterinary science. Both approaches were assessed to have negative welfare impacts, although in neither case were overall welfare scores higher than intermediate, never exceeding 5-6 out of a possible 8. Based on our assessments, the restraint cage approach is no worse for welfare compared to using general anaesthesia and possibly has a lower overall negative impact on badger welfare. Our results can be used to integrate consideration of badger welfare alongside other factors, including financial cost and efficiency, when selecting a field method for blood sampling free-living badgers.

Difference in differences analysis evaluates the effects of the badger control policy on bovine tuberculosis in England

Persistent tuberculosis (TB) in cattle populations in England has been associated with an exchange of infection with badgers (Meles meles). A badger control policy (BCP) commenced in 2013. Its aim was to decrease TB incidence in cattle by reducing the badger population available to provide a wildlife reservoir for bovine TB. Monitoring data from 52 BCP intervention areas 200-1600 km2 in size, starting over several years, were used to estimate the change in TB incidence rate in cattle herds, which was associated with time since the start of the BCP in each area. A difference in differences analysis addressed the non-random selection and starting sequence of the areas. The herd incidence rate of TB reduced by 56% (95% Confidence Interval 41-69%) up to the fourth year of BCP interventions, with the largest drops in the second and third years. There was insufficient evidence to judge whether the incidence rate reduced further beyond 4 years. These estimates are the most precise for the timing of declines in cattle TB associated with interventions primarily targeting badgers. They are within the range of previous estimates from England and Ireland. This analysis indicates the importance of reducing transmission from badgers to reduce the incidence of TB in cattle, noting that vaccination of badgers, fertility control and on farm biosecurity may also achieve this effect.

Spatial association of Mycobacterium bovis infection in cattle and badgers at the pasture interface in an endemic area in France

Despite control and surveillance programmes, Mycobacterium bovis, the main aetiologic agent of bovine tuberculosis (bTB), is still detected on cattle farms and in wildlife populations in France, especially in badgers in the French Côte-d'Or département. The aim of our study was to find out if infected badgers were trapped significantly closer to pastures of infected farms than non-infected badgers and, if so, to determine the most efficient distance around those pastures for badger trapping, particularly for surveillance purposes. We studied two subareas (southern and northern), chosen based on natural barriers to badger movements and according to the presence of pastures belonging to infected farms (POIFs) and infected or non-infected badgers. In each subarea, we computed the shortest distances D0 and D between badgers trapped a given year n between 2015 and 2019 (n = 59 infected and n = 1535 non-infected badgers for D0; n = 53 infected and n = 1476 non-infected badgers for D) and POIFs designated as infected between the year n - 4 and n + 1 (respectively n = 373 and n = 388 POIFs). D0 was calculated without considering spoligotypes, while D was calculated considering the possible epidemiological link between infected badgers and POIFs by using bTB spoligotype information. Then, we computed the observed mean and median of the D0 and D distances and used a bootstrap analysis to test if infected badgers were found significantly closer to POIFs than non-infected badgers. We observed that infection of badgers was not independent of distance from POIF in both subareas but distances (D0 or D) were different between the northern and southern subarea. In the northern subarea, which displays a mosaic landscape (mean and median D distances were respectively 612 m and 303 m for infected badgers), infected badgers indeed were trapped closer to POIFs, considering D0 and D. In the southern subarea, predominantly forested, infected badgers were significantly closer to POIFs than non-infected badgers when considering D0 but not for D (mean and median D distances were respectively 7148 m and 4831 m for infected badgers). These results will help to determine the most efficient distance from POIFs to trap badgers to determine their infection status in countryside landscapes. They also highlight the need to better understand the epidemiological systems at play in more forested landscapes where badgers may behave differently or other susceptible sympatric wild species might play a more important role in the circulation of M. bovis, both phenomena contributing to badger infection at greater distances from POIFs.

Assessing the potential impact of applying a higher sensitivity test to selected cattle populations for the control of bovine tuberculosis in England

Bovine tuberculosis (bTB) continues to be the costliest, most complex animal health problem in England. The effectiveness of the test-and-slaughter policy is hampered by the imperfect sensitivity of the surveillance tests. Up to half of recurrent incidents within 24 months of a previous one could have been due to undetected infected cattle not being removed. Improving diagnostic testing with more sensitive tests, like the interferon (IFN)-gamma test, is one of the government's top priorities. However, blanket deployment of such tests could result in more false positive results (due to imperfect specificity), together with logistical and cost-efficiency challenges. A targeted application of such tests in higher prevalence scenarios, such as a subpopulation of high-risk herds, could mitigate against these challenges. We developed classification machine learning algorithms (using 80% of 2012-2019 bTB surveillance data as the training set) to evaluate the deployment of IFN-gamma testing in high-risk herds (i.e. those at risk of an incident in England) in two testing data sets: i) the remaining 20% of 2012-19 data, and ii) 2020 bTB surveillance data. The resulting model, classification tree analysis, with an area under a receiver operating characteristic (ROC) curve (AUC) > 95, showed a 73% sensitivity and a 97% specificity in the 2012-2019 test dataset. Used on 2020 data, it predicted eight percent (3 510 of 41 493) of eligible active herds as at-risk of a bTB incident, the majority of them (66% or 2 328 herds) experiencing at least one. Whilst all predicted at-risk herds could have preventive measures applied, the additional application of IFN-gamma test in parallel interpretation to the statutory skin test, if the risk materialises, would have resulted in 8 585 additional IFN-gamma reactors detected (a 217% increase over the 2 710 IFN-gamma reactors already detected by tests carried out). Only 18% (330 of 1 819) of incidents in predicted high-risk herds had the IFN-gamma test applied in 2020. We therefore conclude that this methodology provides a better way of directing the application of the IFN-gamma test towards the high-risk subgroup of herds. Classification tree analysis ensured the systematic identification of high-risk herds to consistently apply additional measures in a targeted way. This could increase the detection of infected cattle more efficiently, preventing recurrence and accelerating efforts to achieve eradication by 2038. This methodology has wider application, like targeting improved biosecurity measures in avian influenza at-risk farms to limit damage to the industry in future outbreaks.

Analysis of a multi-type resurgence of Mycobacterium bovis in cattle and badgers in Southwest France, 2007-2019

Although control measures to tackle bovine tuberculosis (bTB) in cattle have been successful in many parts of Europe, this disease has not been eradicated in areas where Mycobacterium bovis circulates in multi-host systems. Here we analyzed the resurgence of 11 M. bovis genotypes (defined based on spoligotyping and MIRU-VNTR) detected in 141 farms between 2007 and 2019, in an area of Southwestern France where wildlife infection was also detected from 2012 in 65 badgers. We used a spatially-explicit model to reconstruct the simultaneous diffusion of the 11 genotypes in cattle farms and badger populations. Effective reproduction number R was estimated to be 1.34 in 2007-2011 indicating a self-sustained M. bovis transmission by a maintenance community although within-species Rs were both < 1, indicating that neither cattle nor badger populations acted as separate reservoir hosts. From 2012, control measures were implemented, and we observed a decrease of R below 1. Spatial contrasts of the basic reproduction ratio suggested that local field conditions may favor (or penalize) local spread of bTB upon introduction into a new farm. Calculation of generation time distributions showed that the spread of M. bovis has been more rapid from cattle farms (0.5-0.7 year) than from badger groups (1.3-2.4 years). Although eradication of bTB appears possible in the study area (since R < 1), the model suggests it is a long-term prospect, because of the prolonged persistence of infection in badger groups (2.9-5.7 years). Supplementary tools and efforts to better control bTB infection in badgers (including vaccination for instance) appear necessary.

The potential risk of international spread of Mycobacterium bovis associated with movement of alpacas

Introduction

The study highlights the transboundary nature of tuberculosis (TB) in alpacas and the failure of current ante-mortem testing protocols (the tuberculin skin and Enferplex Camelid TB tests) to identify TB-free alpaca herds and individuals for export. Our research and the available literature indicate that the alpaca (Vicugna pacos) is extremely susceptible to Mycobacterium bovis infection, and that testing periodicity fails to take into account that animals do not manifest disease symptoms for a long time. The skin test failed to identify Mycobacterium bovis infection in two alpacas prior to their movement from the UK to Poland. The animals were purchased by a breeding centre in Poland, and were then shown at an international animal exhibition. The last owner of the alpacas before their deaths from TB bought the infected animals unwittingly in order to run rehabilitation activities with disabled children on his farm.

Material and Methods

Thoracic lymph node, lung and liver tissue samples obtained at necropsy were examined histopathologically after Ziehl–Neelsen staining. Tissue samples were homogenised and mycobacteria present there were cultured on Stonebrink’s medium during a 6-week incubation. A commercial test using polymorphism of the chromosomal direct repeat region provided species identification and additional identification was by spacer oligonucleotide typing and mycobacteria interspersed repetitive unit–variable number tandem repeat analysis with a gel electrophoresis protocol.

Results

The microbiological examination confirmed multiorgan TB caused by the SB0666 spoligotype of Mycobacterium bovis.

Conclusion

Due to the suboptimal performance of current diagnostic tests for TB in alpacas, there is a risk that infected animals may be moved unwittingly. A risk of TB spread associated with the international movement of alpacas is implied by this study.

Analysis of the impact of badger culling on bovine tuberculosis in cattle in the high-risk area of England, 2009-2020

BACKGROUND

Since 2013, badger culling has been part of the UK Government's strategy for controlling bovine tuberculosis (bTB) within a high-risk area (HRA) in England. Government surveillance data now enables an examination of bTB herd incidence and prevalence, its headline indicators, within and outside cull areas over the period 2009-2020.

METHODS

Analysis compared herd incidence and prevalence data from within and outside badger culling areas. A range of models (GLMs, GLMMs, GAMs and GAMMs) were used to analyse incidence and prevalence in culled and unculled areas using frequentist and Bayesian approaches. Change in incidence across ten county areas within the HRA for the period 2010-2020 was also compared.

RESULTS

Analyses based on Defra published data using a variety of statistical methodologies did not suggest that badger culling affected herd bTB incidence or prevalence over the study period. In 9 of 10 counties, bTB incidence peaked and began to fall before badger culling commenced.

LIMITATIONS

There are limitations around the data available on culling location, temporal information and other confounding factors. As such, further analysis of any future datasets that may be released on bTB levels in areas where badger culling has been implemented is warranted.

CONCLUSION

This examination of government data obtained over a wide area and a long time period failed to identify a meaningful effect of badger culling on bTB in English cattle herds. These findings may have implications for the use of badger culling in current and future bTB control policy.

Development and evaluation of a multi-antigen serological assay for the intra-vitam diagnosis of Tuberculosis caused by Mycobacterium bovis in pigs

Bovine Tuberculosis (bTB) is a chronic disease caused by Mycobacterium bovis, affecting cattle and other mammalian species, such as pigs. In the present work, we developed a novel multi-antigen assay (The TB-Luminex multiplex test) to diagnose bTB in pig sera. Moreover, we investigated the seroreactivity to the different antigens employed (MPB83, MPB70, CFP10 and ESAT6) and the possible correlation with bTB lesions distribution in the positive pigs. The serum samples were collected from 59 bTB positive pigs and 186 pigs reared in an officially Tuberculosis free area. Sera were processed according to an optimized protocol for the detection of antibodies by a multiantigen assay using Luminex technology. The positive group showed visible lesions with localized (54.2%) or generalized (45.8%) distribution. Culture confirmed the infection in 62.7% of the cases, and histopathology and intra-vitam assays were used as additional confirmatory tests. Within the set of antigens tested, the immunodominant was MPB83 (positive in 94.9% of the affected pigs), followed by CFP10, MPB70 and ESAT6 (positivity shown in 81.3%, 67.8% and 25.4% of the positive pigs tested, respectively). The best antigens combination was MPB83/CFP10, with a 96.6% sensitivity and 96.8% specificity. Overall, the test showed high sensitivity (98.3% and 86.4%) and specificity (96.2% and 97.8%), if sera were considered positive according to the positivity to a single antigen or at least two antigens, respectively. The TB-Luminex multiplex test results did not give significantly different outcomes according to lesions distribution. Given the present study results, the TB-Luminex multiplex test is a reliable test capable of detecting bTB in most infected pigs with good Se and Sp, regardless of the stage of the disease. In conclusion, multi-antigen tests can be used as individual tests and screening tools for domestic and wild suids within bTB eradication programs.

The challenge of estimating wildlife populations at scale: the case of the European badger (Meles meles) in Ireland

Estimating population size in space and time is essential for applied ecology and wildlife management purposes; however, making accurate and precise estimates at large scales is highly challenging. An example is the European badger (Meles meles), a widespread and abundant mammal in Ireland. Due to their role in the epidemiology of bovine tuberculosis, the species has been culled in agriculturally dominant landscapes with the intention of reducing spillback infection to local cattle populations. Despite several studies using different approaches having estimated badger populations at different time points and scales, there remains considerable uncertainty regarding the current population and its future trajectory. To explore this uncertainty, we use published data and expert opinion to estimate a snapshot of probable badger population size using a Monte Carlo approach, incorporating variation in three key components: social group numbers, group size, and culling efficacy. Using this approach, we estimate what the badger population in Ireland would be with/without culling, assuming a steady-state population at carrying capacity, and discuss the limitations of our current understanding. The mean estimate for the badger population size was 63,188 (5–95th percentile, 48,037–79,315). Population estimates were sensitive to the assumption of mean group size across landscape type. Assuming a cessation of culling (in favour of vaccination, for example) in agricultural areas, the mean estimated population size was 92,096 (5–95th percentile, 67,188–118,881). Despite significant research being conducted on badgers, estimates on population size at a national level in Ireland are only approximate, which is reflected in the large uncertainty in the estimates from this study and inconsistencies between recording of data parameters in previous studies. Focusing on carefully estimating group size, factors impacting its variation, in addition to understanding the dynamics of repopulation post-culling, could be a fruitful component to concentrate on to improve the precision of future estimates.

Mycobacterial Infection of Precision-Cut Lung Slices Reveals Type 1 Interferon Pathway Is Locally Induced by Mycobacterium bovis but Not M. tuberculosis in a Cattle Breed

Tuberculosis exacts a terrible toll on human and animal health. While Mycobacterium tuberculosis (Mtb) is restricted to humans, Mycobacterium bovis (Mb) is present in a large range of mammalian hosts. In cattle, bovine TB (bTB) is a noticeable disease responsible for important economic losses in developed countries and underestimated zoonosis in the developing world. Early interactions that take place between mycobacteria and the lung tissue early after aerosol infection govern the outcome of the disease. In cattle, these early steps remain poorly characterized. The precision-cut lung slice (PCLS) model preserves the structure and cell diversity of the lung. We developed this model in cattle in order to study the early lung response to mycobacterial infection. In situ imaging of PCLS infected with fluorescent Mb revealed bacilli in the alveolar compartment, in adjacent or inside alveolar macrophages, and in close contact with pneumocytes. We analyzed the global transcriptional lung inflammation signature following infection of PCLS with Mb and Mtb in two French beef breeds: Blonde d'Aquitaine and Charolaise. Whereas, lungs from the Blonde d'Aquitaine produced high levels of mediators of neutrophil and monocyte recruitment in response to infection, such signatures were not observed in the Charolaise in our study. In the Blonde d'Aquitaine lung, whereas the inflammatory response was highly induced by two Mb strains, AF2122 isolated from cattle in the UK and Mb3601 circulating in France, the response against two Mtb strains, H37Rv, the reference laboratory strain, and BTB1558, isolated from zebu in Ethiopia, was very low. Strikingly, the type I interferon pathway was only induced by Mb but not Mtb strains, indicating that this pathway may be involved in mycobacterial virulence and host tropism. Hence, the PCLS model in cattle is a valuable tool to deepen our understanding of early interactions between lung host cells and mycobacteria. It revealed striking differences between cattle breeds and mycobacterial strains. This model could help in deciphering biomarkers of resistance vs. susceptibility to bTB in cattle as such information is still critically needed for bovine genetic selection programs and would greatly help the global effort to eradicate bTB.

Effect of selective removal of badgers (Meles meles) on ranging behaviour during a 'Test and Vaccinate or Remove' intervention in Northern Ireland

The role of the Eurasian badger (Meles meles) as a wildlife host has complicated the management of bovine tuberculosis (bTB) in cattle. Badger ranging behaviour has previously been found to be altered by culling of badgers and has been suggested to increase the transmission of bTB either among badgers or between badgers and cattle. In 2014, a five-year bTB intervention research project in a 100 km² area in Northern Ireland was initiated involving selective removal of dual path platform (DPP) VetTB (immunoassay) test positive badgers and vaccination followed by release of DPP test negative badgers (‘Test and Vaccinate or Remove’). Home range sizes, based on position data obtained from global positioning system collared badgers, were compared between the first year of the project, where no DPP test positive badgers were removed, and follow-up years 2–4 when DPP test positive badgers were removed. A total of 105 individual badgers were followed over 21 200 collar tracking nights. Using multivariable analyses, neither annual nor monthly home ranges differed significantly in size between years, suggesting they were not significantly altered by the bTB intervention that was applied in the study area.

Simulating the next steps in badger control for bovine tuberculosis in England

Industry-led culling of badgers has occurred in England to reduce the incidence of bovine tuberculosis in cattle for a number of years. Badger vaccination is also possible, and a move away from culling was "highly desirable" in a recent report to the UK government. Here we used an established simulation model to examine badger control option in a post-cull environment in England. These options included no control, various intermittent culling, badger vaccination and use of a vaccine combined with fertility control. The initial simulated cull led to a dramatic reduction in the number of infected badgers present, which increased slowly if there was no further badger management. All three approaches led to a further reduction in the number of infected badgers, with little to choose between the strategies. We do note that of the management strategies only vaccination on its own leads to a recovery of the badger population, but also an increase in the number of badgers that need to be vaccinated. We conclude that vaccination post-cull, appears to be particularly effective, compared to vaccination when the host population is at carrying capacity.

Harvest strategies for the elimination of low prevalence wildlife diseases

The intensive harvesting of hosts is often the only practicable strategy for controlling emerging wildlife diseases. Several harvesting approaches have been explored theoretically with the objective of lowering transmission rates, decreasing the transmission period or specifically targeting spatial disease clusters or high-risk demographic groups. Here, we present a novel model-based approach to evaluate alternative harvest regimes, in terms of demographic composition and rates, intended to increase the probability to remove all infected individuals in the population during the early phase of an outbreak. We tested the utility of the method for the elimination of chronic wasting disease based on empirical data for reindeer (Rangifer tarandus) in Norway, in populations with (Nordfjella) and without (Hardangervidda) knowledge about exact disease prevalence and population abundance. Low and medium harvest intensities were unsuccessful in eliminating the disease, even at low prevalence. High-intensity harvesting had a high likelihood of eliminating the disease, but probability was strongly influenced by the disease prevalence. We suggest that the uncertainty about disease prevalence can be mitigated by using an adaptive management approach: forecast from models after each harvest season with updated data, derive prevalence estimates and forecast further harvesting. We identified the problems arising from disease surveillance with large fluctuations in harvesting pressure and hence sample sizes. The elimination method may be suitable for pathogens that cause long-lasting infections and with slow epidemic growth, but the method should only be attempted if there is a low risk of reinfection, either by a new disease introduction event (e.g. dispersing hosts) or due to environmental reservoirs. Our simulations highlighted the short time window when such a strategy is likely to be successful before approaching near complete eradication of the population.

A Bayesian analysis of a Test and Vaccinate or Remove study to control bovine tuberculosis in badgers (Meles meles)

A novel five year Test and Vaccinate or Remove (TVR) wildlife research intervention project in badgers (Meles meles) commenced in 2014 in a 100km2 area of Northern Ireland. It aimed to increase the evidence base around badgers and bovine TB and help create well-informed and evidence-based strategies to address the issue of cattle-to-cattle spread and spread between cattle and badgers. It involved real-time trap-side testing of captured badgers and vaccinating those that tested negative for bTB (BadgerBCG-BCG Danish 1331) and removal of those that tested bTB positive using the Dual-Path Platform VetTB test (DPP) for cervids (Chembio Diagnostic Systems, Medford, NY USA). Four diagnostic tests were utilised within the study interferon gamma release assay (IGRA), culture (clinical samples and post mortem), DPP using both whole blood and DPP using serum. BCG Sofia (SL222) was used in the final two years because of supply issues with BadgerBCG. Objectives for this study were to evaluate the performance of the DPP in field conditions and whether any trend was apparent in infection prevalence over the study period. A Bayesian latent class model of diagnostic test evaluation in the absence of a gold standard was applied to the data. Temporal variation in the sensitivity of DPP and interferon gamma release assay (IGRA) due to the impact of control measures was investigated using logistic regression and individual variability was assessed. Bayesian latent class analysis estimated DPP with serum to have a sensitivity of 0.58 (95% CrI: 0.40-0.76) and specificity of 0.97 (95% CrI: 0.95-0.98). The DPP with whole blood showed a higher sensitivity (0.69 (95% CrI: 0.48-0.88)) but similar specificity (0.98 (95% Crl: 0.96-0.99)). The change from BCG Danish to BCG Sofia significantly impacted on DPP serum test characteristics. In addition, there was weak evidence of increasing sensitivity of IGRA over time and differences in DPP test sensitivity between adults and cubs. An exponential decline model was an appropriate representation of the infection prevalence over the 5 years, with a starting prevalence of 14% (95% CrI: 0.10-0.20), and an annual reduction of 39.1% (95% CrI: 26.5-50.9). The resulting estimate of infection prevalence in year 5 of the study was 1.9% (95% CrI: 0.8-3.8). These results provide field evidence of a statistically significant reduction in badger TB prevalence supporting a TVR approach to badger intervention. They give confidence in the reliability and reproducibility in the DPP Whole Blood as a real time trap-side diagnostic test for badgers, and describe the effect of vaccination and reduced infection prevalence on test characteristics.

Mycobacterium microti: Not Just a Coincidental Pathogen for Cats

Public interest in animal tuberculosis is mainly focused on prevention and eradication of bovine tuberculosis in cattle and wildlife. In cattle, immunodiagnostic tests such as the tuberculin skin test or the interferon gamma (IFN-γ) assay have been established and are commercially available. Feline tuberculosis is rather unknown, and the available diagnostic tools are limited. However, infections with Mycobacterium tuberculosis complex members need to be considered an aetiological differential diagnosis in cats with granulomatous lymphadenopathy or skin nodules and, due to the zoonotic potential, a time-efficient and accurate diagnostic approach is required. The present study describes 11 independent cases of Mycobacterium microti infection in domestic cats in Switzerland. For three cases, clinical presentation, diagnostic imaging, bacteriological results, immunodiagnostic testing, and pathological features are reported. An adapted feline IFN-γ release assay was successfully applied in two cases and appears to be a promising tool for the ante mortem diagnosis of tuberculosis in cats. Direct contact with M. microti reservoir hosts was suspected to be the origin of infection in all three cases. However, there was no evidence of M. microti infection in 346 trapped wild mice from a presumptive endemic region. Therefore, the source and modalities of infection in cats in Switzerland remain to be further elucidated.

Temporal and spatial Mycobacterium bovis prevalence patterns as evidenced in the All Wales Badgers Found Dead (AWBFD) survey of infection 2014-2016

In order to better understand the spatial spread of bovine tuberculosis (bTB) in Wales, an All Wales Badgers Found Dead (AWBFD) survey was carried out from 2014-2016. For Wales, as a whole, there was a significant decrease (p < 0.001) in prevalence of bTB in badgers since a similar survey was carried out in 2005-2006, with a drop from 13.3% to 7.3%. The highest prevalence was observed for the High TB Area East (18.6%), which shares its border with England, and differed significantly (p < 0.001) from the High TB Area West (7.4%). The lowest proportion of carcases diagnosed with the disease (0.7%) was in the Low TB Area, followed by the two Intermediate TB Areas of Wales (2.7%). The M. bovis isolates from badgers tended to be similar to the genotypes of cattle in the same area, except in the Low TB Area. The direction of any cross species transmission and the drivers for this cannot be determined from this study. The spatial variations described here support the need for regionally adapted surveillance and control measures for bovine tuberculosis in Wales.