Research and analysis

Background information: badger control areas monitoring data up to 2022

Published 7 September 2023

Purpose of the monitoring data

APHA is commissioned by Defra to monitor the incidence of bovine tuberculosis (TB) in cattle in geographic areas where badger control has been undertaken under specific licence for culling. To address this requirement APHA publishes monitoring data showing the incidence and prevalence of TB in cattle herds in badger control areas that have been exposed to at least one period of culling and for which there is at least one year of follow-up since culling began.

The data are provided in OpenDocument Spreadsheets (ODS). This report provides background information and methodological details to accompany these data.

The monitoring data are derived from TB tests conducted during routine surveillance and control of TB in cattle. The data do not demonstrate whether the badger control policy has reduced bovine TB in cattle. Evaluation of the effect of the badger control policy requires consideration of other factors that could affect cattle TB incidence in addition to culling. This has been subject to separate independently reviewed and published analytical studies (Brunton et al., 2017; Downs et al., 2019).

Background to the badger control policy

Bovine tuberculosis (TB) is an infectious, zoonotic (can infect humans) bacterial disease of cattle and other mammals (About bovine TB), with a significant wildlife reservoir (that is, badgers) present in large areas of England. The badger control policy encompassing badger culling was implemented in England to reduce the population of badgers where TB is endemic. The aim of the policy is to reduce the potential for transmission of Mycobacterium bovis, the bacterium that causes TB, between badgers and cattle, and hence reduce the incidence of TB in cattle.

The policy is based upon evidence generated by the Randomised Badger Culling Trial (RBCT) conducted in England between 1998 and 2005. The incidence of confirmed cattle herd TB incidents was around 29% (95% confidence interval 21 to 36%) lower in areas where proactive culling was conducted, relative to non-intervention areas (Donnelly et al., 2007; Jenkins et al., 2010). Increased risks of TB were observed in cattle herds on land adjoining land where culling was conducted although the increased risk did not persist once culling had stopped.

Further information on the badger control policy and how badger culling helps deliver the aim of Officially TB Free (OTF) status for England can be found in the following publications: The Government’s policy on Bovine TB and badger control in England and The Strategy for achieving Officially Bovine Tuberculosis Free status for England.

Current badger control policy

The current badger control policy includes licensing of industry-led badger culling (Defra, 2021) since 2013 and provision of biosecurity advice to farmers in licensed areas since 2014.

There are currently three types of badger culling licence in use in England (Badger culling - Bovine TB):

1. Badger Disease Control licence (applicable to the High Risk Area (HRA) and Edge Area of England, and has a duration of four years)
2. Supplementary Badger Disease Control licence (applicable to areas that have completed at least four years of culling under a Badger Disease Control licence, and to date has a duration of up to five years)
3. Low Risk Area Badger Disease Control licence (applicable to the Low Risk Area (LRA) of England)

Badger culling licences are issued under the Protection of Badgers Act 1992. Between 2013 and 2022, licences were issued by Natural England (NE). Licences apply to pre-defined badger control areas, the boundaries of which are defined by NE. Under all licences, culling is initiated in the autumn and continues for a period of around 6 weeks until badger removal targets are met.

Since 2020, APHA has also deployed badger vaccination in parts of some badger control areas, for example, in Area 32-Cumbria, which has been granted a Low Risk Area Badger Disease Control licence (Summary of badger vaccination in 2020). Badger vaccination requires a separate licence under the Protection of Badgers Act 1992, which are also issued by Defra and NE (Licences to cage-trap and mark badgers for bovine TB vaccination). The occurrence of badger vaccination within the boundaries of a badger control area may result in a reduction of accessible land available for badger culling. Information relating to operations in badger control areas up to the end of 2022 can be found at the following pages: Summary of 2022 badger control operations, Summary of 2022 supplementary badger control operations and Bovine TB: hotspots in the Low Risk Area of England. The number of badgers vaccinated per county across England in 2022 can be found via the following link Summary of badger vaccination in 2022.

The main changes to TB surveillance and control policies over time affecting cattle in badger control areas are listed below.

Changes to TB testing frequency that can affect TB incidence and prevalence

Reported incidence and prevalence of TB reflects the background force of infection but also surveillance and control policies, which, themselves, affect the detection of disease. Surveillance and control policies, including the frequency of routine testing for TB in cattle and the types of tests applied, can differ across the TB risk areas and therefore can differ between badger control areas. The main changes to TB surveillance and control policies up to the end of 2022 affecting cattle in badger control areas are listed below. Further information about TB tests and surveillance and control policies can be found on the TBhub (Bovine TB Testing in Cattle, Cows).

1. Prior to 2013, when the badger control policy started, most cattle herds in counties now in the HRA were subject to routine annual field surveillance for TB using the tuberculin skin test. Most counties in the Edge Area, as it is now known, were subject to field surveillance every two years, although there was some variation in this.
2. In 2013 all herds in the Edge Area became subject to routine annual surveillance.
3. In 2015 part of the county of Cheshire in the Edge Area became subject to routine 6-monthly testing because the area was recognised as having a particularly high risk of infection.
4. In 2018 routine 6-monthly testing was applied to all of Cheshire, Oxfordshire and Warwickshire and parts of Berkshire, Hampshire and Derbyshire in the Edge Area (Expansion of the Edge Area and cattle testing arrangements).
5. In September 2020 routine 6-monthly testing was applied to the HRA counties of Staffordshire and Shropshire.
6. In July 2021 routine 6-monthly testing was applied to the remainder of the HRA (Animal and Plant Health Agency, 2021a; Six-monthly surveillance testing of cattle herds in the HRA). Herds in counties subject to 6-monthly testing can revert to annual testing upon meeting criteria which demonstrates a lower risk of infection (Earned Recognition).
7. From 2017 to 2021, mandatory IFN gamma testing to detect and remove infection was applied to herds with a confirmed TB incident, a chronic/persistent breakdown, and within the HRA in areas that had been subject to two or more years of culling.
8. Since July 2021, the gamma testing policy has changed in the HRA and six-monthly testing Edge Area, where confirmed TB incident herds are tested if they are within 18 months of the herd regaining OTF status (Refinements to the IFN gamma testing policy in the HRA and Edge Area). The policy remains the same for the annual testing Edge Area and the LRA.
9. From 23 March 2020, skin testing for select purposes was not mandatory for cattle under 180 days old due to the COVID-19 outbreak (Advice for OVs on a temporary amendment to testing bovine animals under 180 days old in Officially TB-Free herds in England and Wales during the COVID-19 outbreak). Short interval tests, which are required to restore a herd’s OTF status, were not originally included in this derogation. However, herds were considered on a case-by-case basis with extensions granted to time windows to perform short interval tests (Advice for OVs undertaking TB testing during the COVID-19 outbreak in England). These temporary amendments to TB skin testing due to COVID-19 were discontinued in July and August 2021 (Discontinuing Covid-19 temporary amendments to TB skin testing in GB).

Badger control areas included in the latest monitoring data

Badger culling licences were issued to groups of farmers and landowners in England across a total of 61 badger control areas between 2013 and 2021. This included two licences issued in 2013, one licence in 2015, seven licences in 2016, and 11 licences in each of 2017, 2018, 2019 and 2020. A further seven licences were issued in 2021. The majority of areas are located in the HRA, but 12 straddle the HRA and Edge Area and four are located entirely in the Edge Area. Two are located entirely in the LRA for TB in England (linked to TB Hotspots) with licences issued for Low Risk Area Badger Disease Control purposes. As of the end of 2022, badger culling operations remained active in 58 of the badger control areas covered in this report (Summary of 2022 badger control operations, Summary of 2022 supplementary badger control operations). Licensed badger culling operations concluded in Areas 1, 2 and 32 at the start of 2022.

Each badger control area has a unique identifier, which relates to when the area was licensed for badger culling and the county in which it is located. The boundaries of these areas are defined and provided by NE to APHA each year. They have remained broadly stable over time, with small revisions to some boundaries by NE from time to time. The percentage change to badger control areas due to boundary revisions over time since the first year of badger culling in each badger control area up to the end of 2021 is shown in Table 1.

Table 1 Percentage change to badger control areas due to boundary revisions up to the end of 2021, and the dates any changes were implemented.

Badger control area	Percentage area changes
Area 08 - Dorset	+ 3.2% in April 2017
Area 13 - Devon	+ 9.4% in May 2018
Area 15 - Devon	+ 0.6% in May 2018
Area 19 - Wiltshire	+ 3.5% in May 2018 (1)
Area 20 - Wiltshire	+ 1.3% in May 2018
Area 24 - Devon	+ 6.1% in February 2019
Area 32 - Cumbria	+ 12.7% in January 2019 (2),(3)
Area 34 - Cheshire	+ 19.8% in August 2020
Area 35 - Cornwall	+ 0.3% in August 2021
Area 37 - Devon	+ 0.3% in August 2020
Area 40 - Herefordshire	+ 0.3% in August 2020
Area 44 – Avon	+ 24.2% in August 2021
Area 47 – Herefordshire	+ 11.5% in August 2021
Area 50 – Shropshire	+ 1.1% in August 2021
Area 51 – Somerset	+ 3.0% in August 2021
Area 52 – Warwickshire	+ 11.8% in August 2021
Area 53 – Wiltshire	+ 4.6% in August 2021
Area 54 – Lincolnshire	+ 19.1% in August 2021

(1) The boundary of Area 19 has remained unchanged since 2018. However, in 2021 there was a small change to the proportion of the area subject to culling due to the presence of badger vaccination.

(2) The boundary of Area 32 has remained unchanged since 2019. However, since 2020 there have been annual changes to the proportion of the area subject to culling due to a gradual switch to badger vaccination. Further information on the vaccination occurring within Area 32 can be found on Bovine TB: hotspots in the Low Risk Area of England.

(3) The 2021 monitoring report incorrectly stated that Area 32 reduced in size in 2020. The data published in the ODS accompanying the 2021 report is unaffected by this error.

Monitoring methods

Data source and quality

TB data are extracted from Sam, the APHA database, which records the results from TB tests conducted in cattle herds throughout Great Britain. Data were downloaded on 12-April-2023.

These data are compiled over time as a result of TB surveillance activities and control policies and historical data may be updated or corrected in light of new information. Corrections may include removal of a herd that has become inactive, inclusion of a herd that has become active, and revisions to the geographical location of the herd. Herd TB incident designation may also change from unconfirmed infection (Officially Tuberculosis Free- Suspended, OTF-S) to confirmed infection (Officially Tuberculosis Free- Withdrawn, OTF-W) due to confirmatory information about the presence of M. bovis infection becoming available since the previous report was published. Data corrections and routine validation can affect the counts of incidents and the calculated time at risk. The corrections in the past have generated minor differences in statistics between annual reports, particularly in relation to the year prior to the most recent year in the report. The most recently published monitoring data contain the most accurate current and historical data known to the project team.

Time period

Monitoring data are provided for calendar years and intervention years. Each badger control area has its own associated baseline date, which is the start date of the first cull in that area. An intervention year is the period of 12 months starting from the same day and month of the baseline date for each year in the reporting period and is defined separately for each area.

The starting year reported, and the number of follow-on years is dependent on when the start date of the first cull in that area took place. Data four years prior to the baseline date for each badger control area is also included.

Monitoring herd groups

Cohort

Cohort herds are herds recorded as active in badger control areas on the baseline date for that area. We can therefore assume them to be exposed to badger control operations for the full follow-up period whilst they remain active. Only changes in activity of the herd e.g., loss of herds from farms that are no longer operating, will affect the cohort. This means that the number of herds in the cohort can decrease but not increase between years following the first year of culling in that badger control area. The cohort population is not affected by changes to cull area boundaries.

Herds in existence (HIE)

HIE provides an annual snapshot of active herds that are located within badger control areas at the time data are compiled for the annual monitoring report. The APHA reports levels of TB for the population of HIE based on the most up-to-date boundary information provided by NE. The herd count for HIE includes new herds that come into existence before and after the baseline date. Inclusion of the HIE population should help account for any bias due to the natural loss of herds from the cohort due to changes in business activity. However, it is important to note that herds included in this group were not all active on the baseline date for the area, and therefore may not have been exposed to badger control operations for the entire follow-up period.

Whilst the list of herds in the cohort remains unchanged, the HIE data are redefined for each reporting year for each area due to boundary area changes or changes in herd activity status. The data are reported for the maximum area known to have ever been culled under licence at the time the monitoring data were compiled.

Individual area monitoring data

The monitoring data include the number of all TB incidents, OTF-W incidents, number of herds, herd years at risk, OTF-W incidence and prevalence and numbers of reactors by intervention year and calendar year for both cohort herds and Herds in Existence (HIE) within each badger control area.

Values in cells representing data for areas with fewer than 10 herds in total (incorrectly reported as ’10 or fewer herds’ in the previous report) have been omitted to ensure the confidentiality of individual herd owners. This cut-off value is used by the Office for National Statistics (ONS) (Office for National Statistics, n.d.; Welpton, 2019).

Glossary of definitions

Baseline date

The baseline date is the start date of the cull in each area.

All incidents and OTF-W incidents

All incidents refer to the total number of TB incidents (newly detected infection) in a herd during the reporting period e.g. intervention year or calendar year. It is the sum of Officially Tuberculosis Free-Withdrawn (OTF-W) and Officially Tuberculosis Free-Suspended (OTF-S) incidents detected. Both OTF-W and OTF-S are incidents of TB in a herd that have been disclosed through TB surveillance. However, in OTF-W incidents, M. bovis infection has been confirmed through post-mortem tests in at least one animal from the herd. For incidence data, OTF-W incidents refers to the number of OTF-W incidents detected throughout the reporting period. For prevalence data, the OTF-W incidents refers to the number of OTF-W incidents on the last day of the reporting period (intervention year or calendar year).

Number of herds

The number of herds refers to the number of active herds in a badger control area for each group (cohort or HIE) at either the start (for incidence) or end (for prevalence) of each reporting period, for example, intervention or calendar year.

Time at risk (TAR)

The TAR is the total period of time the herds in a badger control area were considered at risk of TB infection (Defra, 2015; Downs et al., 2013). Herds are considered to be at risk of infection when they are not under trading restrictions because of TB infection (i.e., an incident) in the herd. The TAR is reported in years and is calculated from day one of the reporting period to the final day of the reporting period.

OTF-W incidence rate

The OTF-W incidence rate is the rate of occurrence of OTF-W incidents over the reporting period. The rate is calculated as the number of OTF-W incidents, divided by the TAR and is reported as incidents per 100 herd years at risk (Defra, 2015; Downs et al., 2013). OTF-W incidence is used as the primary outcome for monitoring rather than total TB incidence (which includes OTF-W and OTF-S incidents) because stronger associations have been shown between OTF-W incidence and culling (Donnelly et al., 2007, Downs et al 2019).

OTF-W prevalence

The OTF-W prevalence is a point prevalence measurement indicating the proportion of herds under trading restrictions due to an OTF-W incident on the last day of each reporting period. OTF-W prevalence provides an indication of the burden of disease in a badger control area.

Skin test reactors

Skin test reactors are cattle that reacted to the Single Intradermal Comparative Cervical Tuberculin (SICCT) test, which is the primary screening test for TB in cattle in the UK. The yearly count of reactors relates to the date reactors were detected, not necessarily the year the incident started. Therefore, the count can include reactors from incidents which started in previous years.

The data do not include any cattle removed as “Direct Contacts (DC)”. These are non-reactor animals which are slaughtered because they are considered to be at high risk of being infected, normally as a result of contact with infected cattle.

Interferon (IFN) gamma reactors

IFN gamma reactors are cattle that tested positive to the IFN gamma assay, which is a rapid whole blood in-vitro assay to detect immune response to M. bovis infection for the diagnosis of bovine TB.

Antibody test reactors

Antibody test reactors are cattle that tested positive to an antibody detection assay, which detects whether the animal is generating an immune response to a current M. bovis infection.

Reactors to the SICCT test, the IFN gamma assay and the Antibody test are included within the count of skin test reactors but are not included within the count of IFN gamma or Antibody test reactors. Reactors to both the IFN gamma assay and the Antibody test (but not the SICCT test) are included within the count of IFN gamma reactors but are not included within the count of Antibody test reactors. These counts include all reactors detected during a breakdown, including any at a short interval skin test.

Changes to the monitoring report over time

1. Since the 2018 monitoring report, no data from unculled comparison areas are included because of the loss of land (to culling) which might have been used to compare TB incidence rates in cattle to rates in cull areas.
2. Since the 2021 monitoring report, TB and herd data are no longer reported for buffer areas surrounding central badger control areas. This is because over time the proportion of the buffer area remaining around badger control areas has decreased, with substantial deductions in some areas (Animal and Plant Health Agency 2021b, Table 1) due to the licensing of new cull areas. Additionally, remaining buffer is often comprised of small, separated areas of land which contain small numbers of herds. The overall reduction of available buffer land and the division of remaining buffer into small segments diminishes its value in an analysis of effects from culling.
3. Since the 2022 monitoring report, figures will no longer be included to display the monitoring data due to the large number of areas now reported. All data which were displayed in the figures are still available in the OpenDocument Spreadsheets.
4. Since the 2022 monitoring report, 95% confidence intervals will no longer be provided with the monitoring data. This is to allow data users to calculate confidence intervals using their preferred method.

Bibliography

Animal and Plant Health Agency (2021a) Setting routine surveillance TB testing intervals in 2021 (England)

Animal and Plant Health Agency (2021b) Bovine TB: incidence of TB in cattle in licensed badger control areas in 2013 to 2020.

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