Recurrent bovine tuberculosis in New Zealand cattle and deer herds, 2006–2010

Once bitten twice shy: Risk factors associated with bovine tuberculosis recurrence in Castilla y Leon, Spain

Persistence of bovine tuberculosis (bTB) in cattle herd remains a major challenge in disease elimination due to the ineffectual removal of all infected animals in a bTB breakdown. Characterization of herds with a higher probability of experiencing further bTB breakdowns can help to implement specific risk-based policies for disease control and eradication. Here, our aim was to identify herd- and breakdown-level risk factors in bTB infected herds in Castilla y Leon, Spain, associated with a decreased time to recurrence and an increased risk of recurrence using a mixed effects Cox proportional hazards model and a multivariable logistic regression model, respectively. Results revealed that location (province), herd size and number of incoming animals/contacts were good predictors of a decreased time to bTB recurrence and an increased risk of becoming a recurrent herd. Additionally, the duration of the previous outbreak and the number of IFN-γ herd-tests applied in it were associated with increased odds of (an early) recurrence. Risk factors identified here can be used for early identification of herds in which bTB eradication may be more challenging and that should thus be subjected to increased control efforts. The characterization of high-risk herds may help to minimize the risk of reinfection and emphasize early detection and removal of bTB positive animals in the herd.

Future Risk of Bovine Tuberculosis (Mycobacterium bovis) Breakdown in Cattle Herds 2013-2018: A Dominance Analysis Approach

Bovine tuberculosis (bTB) remains a significant endemic pathogen of cattle herds, despite multi-decadal control programmes being in place in several countries. Understanding the risks of future bTB breakdown (BD) and the associated characteristics of herds and index breakdowns could help inform risk categorisation. Such risk categories could then contribute to tailored management and policies. Here, we estimated the future risk of herd BD for the cohort of herds that were derestricted during 2013 in Ireland using multivariable logit regression models, with a dominance analysis approach. One third of herds that were derestricted in 2013 experienced a breakdown during the follow-up five year period (1469/4459; 33%). BD length was a significant predictor of future risk, primarily driven by long BDs > 230 days relative to short BDs < 130 days (OR 95%CI: 1.157–1.851), as was having had a previous BD (OR 95%CI: 1.012–1.366). Herd-size was the dominant predictor of future risk (accounted for 46% of predicted variance), suggesting significant increase in risk of future breakdown with increasing (log) herd-size (OR 95%CI: 1.378–1.609). There was significant spatial variation in future risk across counties, and it was the second most dominant predictor of future risk (25% of predicted variance). The size of index breakdowns was not a strong predictor of future risk over a 5-year period. These findings can inform a risk-based policy development.

Can bovine TB be eradicated from the Republic of Ireland? Could this be achieved by 2030?

Background

There has been an ongoing decline in bovine tuberculosis (TB) in the Republic of Ireland, however, TB has yet to be eradicated. Further to a recent commitment by the Irish government to eradicate TB by 2030, this paper considers two questions, ‘Can bovine TB be eradicated from the Republic of Ireland?’ and ‘Could this be achieved by 2030?’, given current knowledge from research.

Main body of the abstract

Until very recently, Ireland has lacked key tools required for eradication. This gap has substantially been filled with the national roll-out of badger vaccination. Nonetheless, there is robust evidence, drawn from general national research, international experiences, and results of a recent modelling study, to suggest that all current strategies plus badger vaccination will not be sufficient to successfully eradicate TB from Ireland by 2030. We face a critical decision point in the programme, specifically the scope and intensity of control measures from this point forward. Adequate information is available, both from research and international experience, to indicate that these additional measures should broadly focus on adequately addressing TB risks from wildlife, implementing additional risk-based cattle controls, and enhancing industry engagement. These three areas are considered in some detail.

Conclusion

Based on current knowledge, it will not be possible to eradicate TB by 2030 with current control strategies plus national badger vaccination. Additional measures will be needed if Ireland is to eradicate TB within a reasonable time frame. Decisions made now will have long-term implications both in terms of time-to-eradication and cumulative programme costs.

Spatiotemporal analysis of prolonged and recurrent bovine tuberculosis breakdowns in Northern Irish cattle herds reveals a new infection hotspot

Despite a state-led eradication programme, bovine tuberculosis (bTB) remains endemic in Northern Ireland (NI). Of particular concern are "chronic" prolonged and recurrent bTB breakdowns, which represent significant financial and administrative burdens. However, little is known regarding the spatiotemporal distribution of chronic breakdowns in NI. We therefore analysed both the spatial and spatiotemporal distributions of chronic bTB breakdowns between 2004 and 2014. Significantly positive values for Moran's Index of spatial autocorrelation were found, and Local Moran's I clustering was employed to assess for spatial associations in the number and prevalence of chronic bTB breakdowns across NI. Additional spatio-temporal analysis using SaTScan showed that the burden of chronic bTB infection tends to be found where bTB levels are already high. However, a novel hotspot was revealed wherein the prevalence of chronic breakdowns was higher than expected; this should be the subject of follow-up surveillance.

Explanation and Elaboration Document for the STROBE-Vet Statement: Strengthening the Reporting of Observational Studies in Epidemiology-Veterinary Extension

The STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement was first published in 2007 and again in 2014. The purpose of the original STROBE was to provide guidance for authors, reviewers, and editors to improve the comprehensiveness of reporting; however, STROBE has a unique focus on observational studies. Although much of the guidance provided by the original STROBE document is directly applicable, it was deemed useful to map those statements to veterinary concepts, provide veterinary examples, and highlight unique aspects of reporting in veterinary observational studies. Here, we present the examples and explanations for the checklist items included in the STROBE-Vet statement. Thus, this is a companion document to the STROBE-Vet statement methods and process document (JVIM_14575 "Methods and Processes of Developing the Strengthening the Reporting of Observational Studies in Epidemiology-Veterinary (STROBE-Vet) Statement" undergoing proofing), which describes the checklist and how it was developed.

A review of risk factors for bovine tuberculosis infection in cattle in the UK and Ireland

Bovine tuberculosis (bTB) is an important disease of cattle caused by infection withMycobacterium bovis, a pathogen that may be extremely difficult to eradicate in the presence of a true wildlife reservoir. Our objective was to identify and review relevant literature and provide a succinct summary of current knowledge of risk factors for transmission of infection of cattle. Search strings were developed to identify publications from electronic databases to February 2015. Abstracts of 4255 papers identified were reviewed by three reviewers to determine whether the entire article was likely to contain relevant information. Risk factors could be broadly grouped as follows: animal (including nutrition and genetics), herd (including bTB and testing history), environment, wildlife and social factors. Many risk factors are inter-related and study designs often do not enable differentiation between cause and consequence of infection. Despite differences in study design and location, some risk factors are consistently identified, e.g. herd size, bTB history, presence of infected wildlife, whereas the evidence for others is less consistent and coherent, e.g. nutrition, local cattle movements. We have identified knowledge gaps where further research may result in an improved understanding of bTB transmission dynamics. The application of targeted, multifactorial disease control regimens that address a range of risk factors simultaneously is likely to be a key to effective, evidence-informed control strategies.

The effectiveness of parallel gamma-interferon testing in New Zealand's bovine tuberculosis eradication programme

In bovine tuberculosis (bTB) eradication programmes, especially where prevalence is low, sensitivity of testing in infected herds must be maximised to reduce the possibility of recrudescence of prior infection and the risk to other herds via animal movement. The gamma-interferon (γ-IFN) assay applied in parallel with intradermal tuberculin testing has been shown to increase test sensitivity. The aim of this work was to substantiate this effect in the field. A retrospective observational study was conducted on 239 New Zealand cattle breeding and dairy herds with bTB infection between 1 July 2011 and 1 September 2015 to evaluate the outcomes of new policy introduced in 2011. The investigation defined the number and proportion of reactors (animals testing positive and slaughtered) found with lesions of bTB in intradermal caudal fold testing (CFT) and parallel γ-IFN testing, at the breakdown test or first whole herd test after breakdown, WHT(1), and at the final or projected final whole herd test, WHT(F). Parallel γ-IFN testing was used in 26.8% of the 239 herds at WHT(1), and 430 animals in 49 herds were deemed reactors. One hundred and sixty (37.2%) of these reactors from 32 herds were found to have bTB lesions, despite having been negative to caudal fold testing. These 160 infected animals accounted for 29.6% of all infection found at WHT(1). At WHT(F), parallel γ-IFN testing was conducted on 93 herds and detected a total of 122 reactors in 49 herds, in addition to those found by CFT. Twenty-one of these reactors, from 13 herds, had bTB lesions at slaughter, accounting for 67.7% of all reactors found with bTB at WHT(F). Eleven of these 13 herds would have had their movement restrictions revoked based on a negative herd CFT alone, and could potentially have caused outward transmission of bTB to other herds, as well as experiencing recrudescent breakdowns. We conclude that γ-IFN testing in infected herds, in parallel with intradermal tuberculin testing, is a valuable tool in a bTB eradication programme, as it enables higher test sensitivity at both herd and animal level. The use of the γ-IFN test over a risk cohort early in a breakdown assists in removal of early infection and some cases of anergy to intradermal tuberculin testing. Parallel γ-IFN with compulsory slaughter of reactors should be considered in breeding and dairy herds in conjunction with tuberculin testing before movement control is revoked, and will assist in achieving TB freedom on a herd level and nationally.