Research and analysis

Cumbria (Low Risk Area) year end report 2023

Published 19 September 2024

Applies to England

Introduction

The Low Risk Area (LRA) was established in 2013, along with the Edge and High Risk Areas of England. In 2014 the 3 bovine tuberculosis (TB) risk areas were incorporated into the UK government’s strategy to achieve Officially TB Free (OTF) status for England by 2038. A key action was to recognise the different levels of TB in different parts of the country and to adjust the approaches to TB surveillance and control in each risk area accordingly. Overall, the LRA has a very low and stable incidence of TB infected herds. The current strategy for the LRA seeks to mitigate the risk of TB incursions via cattle movements and rapidly contain and eradicate any foci of infection through:

• mandatory pre- and post- movement testing of cattle entering the LRA from higher risk areas of the UK
• more sensitive testing of infected herds
• temporarily enhanced TB surveillance (radial and hotspot testing) in the vicinity of herds experiencing lesion and/or PCR (Polymerase Chain Reaction) test (or culture) positive incidents of TB

The aim of this combined approach is to preserve the favourable disease status of this area so that its counties can be declared OTF as soon as possible.

This report describes the frequency and geographical distribution of TB in 2023 in cattle herds in Cumbria, which is part of the LRA. In 2023, 13% of all new TB incidents in the LRA were detected in Cumbria.

TB in cattle and other mammals is primarily caused by infection with the bacterium Mycobacterium bovis (M. bovis) and the disease is subsequently referred to as ‘TB’ in this report. Although other sources may refer to TB ‘breakdowns’, this report will use the term ‘incidents’ throughout.

This report is intended for those involved in the control of TB, both locally and nationally. This includes, but is not limited to:

• cattle farmers
• government and private veterinarians
• policy makers
• the scientific community

Details of the data handling methodology used in this report, a glossary of terms, and the TB control measures adopted in the LRA, can be found in the explanatory supplement for the annual reports 2023.

Types of TB incident

Unless otherwise specified, this report includes all new TB incidents detected during the reporting period, 1 January to 31 December 2023. This includes both ‘Officially Tuberculosis-Free Status Withdrawn’ (OTF-W) and ‘Officially Tuberculosis-Free Status Suspended’ (OTF-S) incidents.

OTF-W incidents are those involving at least one skin test reactor (an animal positive to the Single Intradermal Comparative Cervical Tuberculin [SICCT] test) with either:

• typical lesions of TB identified at post-mortem (PM) meat inspection
• and at least one animal with M. bovis-positive PCR test or bacteriological culture results in tissue samples collected from carcasses during the PM inspection

OTF-S incidents are triggered by reactors to the skin test, but without subsequent detection of TB lesions or positive PCR test (or culture) results in any of those animals.

Cattle industry

Cumbria has approximately 433,500 cattle in 2,748 herds, equally distributed between beef and dairy farms. Cattle herd sizes vary across the region, as shown in Appendix 1.

There are 10 livestock markets in Cumbria, 7 of which are approved by APHA to hold slaughter gatherings of cattle from OTF herds that are eligible for, but have not been subjected to, pre-movement TB testing (known as ‘TB pre-movement testing-exempt’ markets). The county has one Licensed Finishing Unit (LFU).

The number of cattle markets in operation in 2023 is captured and maintained centrally by the APHA TB Customer Service Centre. Where possible, this data is then subject to further validation by APHA veterinarians subject to their best knowledge of the local area. Some small discrepancies may therefore exist where changes to markets were not captured in time for this report.

There is frequent movement of cattle from Cumbria into Scotland, as well as a significant number of cattle entering the county from Northern Ireland and the Republic of Ireland. These cattle are generally destined for beef finishing or fattening units. Pedigree breeding bulls from Northern Ireland also move onto Cumbrian farms.

New TB incidents

In 2023, the total number of new TB incidents decreased by 5 compared to 2022 (from 22 to 17), as shown in Figure 1. The number of total incidents in this county has been on a decreasing trajectory since 2017, when there were 33 incidents. In 2023, the number of OTF-S incidents decreased from 15 to 9, whilst OTF-W incidents increased from 7 to 8.

At the time of writing this report, the county has 3 active TB hotspot areas, Confirmed Hotspot 21 (HS21) in East Cumbria, Confirmed Hotspot 29 (HS29) also in East Cumbria (adjoins HS21 to the north-west) and Potential Hotspot 26 (HS26) in the south of the county. M. bovis infected wildlife (badgers) have been detected in the first 2 of those hotspot areas. HS29 was formally established early in 2023. HS21 and HS26 had been in place since 2016 and 2019 respectively. The areas covered by all these hotspots are shown in Figure 3 and are described in more detail later in this report.

In HS21 there were 4 new OTF-S TB incidents in 2023. In HS29, there were 6 new TB incidents (one OTF-S and 5 OTF-W). This is one less incident than in the same area in 2022, however only 3 of these were OTF-W. Together, HS21 and HS29 accounted for 59% of the new incidents in Cumbria in 2023. There were no new TB incidents in HS26 in 2023.

Year	OTF-W	OTF-S	Total
2014	5	15	20
2015	11	20	31
2016	16	16	32
2017	12	21	33
2018	9	18	27
2019	5	24	29
2020	4	19	23
2021	7	11	18
2022	7	15	22
2023	8	9	17

Figure 1: Annual number of new TB incidents in Cumbria, from 2014 to 2023.

Figure 1 description: Stacked bar chart showing the number of new OTF-W and OTF-S incidents detected in Cumbria between 2014 and 2023. OTF-W incidents are shown in blue and OTF-S incidents are shown in green. There were 8 new OTF-W incidents and 9 new OTF-S incidents in 2023, as described in the main body of text.

The headline cattle TB statistics for each county are summarised in Appendix 2.

Disclosing test type

Most new TB incidents were identified through risk-based enhanced surveillance testing, including 6 by radial testing (RAD) and 5 by specific hotspot testing (HS). These 2 test types were also responsible for disclosing the greatest proportion of incidents in 2022 (7 by radial testing and 5 by hotspot testing).

One incident was disclosed by a tracing test due to its links to another OTF-W incident in the same area of Cumbria, as displayed in Figure 2. Two incidents were detected using routine (4-yearly) herd testing (RHT), which was an increase from one incident in 2022. Slaughterhouse surveillance identified one new TB incident in 2023, decreasing from 2 in 2022.

Disclosing test type	Number of new TB incidents
Other	1
Hotspot test	5
Post-movement test	1
Radial test	6
Routine herd test	2
Slaughterhouse	1
Tracing test	1

Figure 2: Number of new TB incidents (OTF-W and OTF-S) in Cumbria, in 2023 according to the surveillance method that detected them.

Figure 2 description: Bar chart showing which tests detected the new TB incidents in Cumbria in 2023. Most new incidents were detected by radial testing (6), followed by hotspot testing (5) and routine herd testing (2).

Duration of TB incidents

A total of 22 TB incidents were resolved during 2023. Of these, 11 were new TB incidents that started in 2023 and 11 started in 2022.

Of the 22 TB incidents that closed in 2023, none were persistent (under movement restrictions for more than 550 days). Nine of those 22 were OTF-W incidents. Seven of these were resolved within 240 days, and the other 2 were resolved between 241 and 550 days (within 266 and 276 days). In 2022 there was only one OTF-W incident resolved between 241 and 550 days. Most OTF-S incidents (8 out of 13) were resolved within 150 days. The other 5 were resolved between 241 and 550 days. There were no resolved OTF-S incidents which had been open for more than 550 days, whereas in 2022, there were 2 which had been under restriction for 544 and 558 days).

Six TB incidents were ongoing at the end of 2023 in Cumbria.

Unusual TB incidents

An explosive OTF-W incident disclosed in a large dairy and beef herd in north-west Cumbria, significantly contributed to this marked increase in the number of animals removed for TB control reasons in 2023. In total, 121 reactors were identified and removed: 76 skin reactors and 45 interferon gamma reactors.

Clade B6-51 was isolated from this incident. This clade is relatively novel in Great Britain (England, Scotland and Wales (GB)), and the isolate was at least 66 Single Nucleotide Polymorphisms (SNPs) apart from any other isolate in the GB database. There is a distant branch of the same clade, which is associated with imported cattle from Northern Ireland, however there were no imported cattle in the affected herd. The origin of the incident remains obscure, but one possible risk pathway could involve contact with contiguous imported cattle.

There was subsequently another OTF-W incident in Cumbria in 2024 that yielded a B6-51 isolate, which was one SNP distance apart from the 2023 isolates from the TB incident described above. However, this incident was clearly due to a traced animal that came from the explosive OTF-W incident in Cumbria.

TB in other species

There is no statutory routine TB surveillance of non-bovine species, apart from post-mortem examination (PME) of animals slaughtered for human consumption, or carcasses submitted to veterinary laboratories for diagnostic investigations. Targeted TB testing takes place in non-bovine herds under TB movement restrictions due to laboratory-confirmed incidents of M. bovis infection, and in specific herds of camelids, goats and captive deer at an elevated risk of infection. There were no reports of TB in other farmed or captive non-bovine species in Cumbria during 2023.

Recurring TB incidents

Three-year recurrence

In Cumbria, one of the 9 (11%) herds with a new OTF-S TB incident in 2023, and one of the 8 (13%) with an OTF-W incident, had experienced another TB incident in the previous 3 years), as shown in Figure 3. The 2023 total recurrence rate for Cumbria in the last 3 years was 12%. This is the lowest total recurrence compared to neighbouring LRA counties (North East (33%), North West (29%), Yorkshire and Humberside (17%) and the second lowest recurrence rate of all LRA counties, in the same time period, although it should be remembered that this reflects the generally low number of incidents.

TB incident	No history of TB in the last 3 years	History of TB in the last 3 years
OTFS	8	1
OTFW	7	1

Figure 3: Number of herds with a TB incident (by OTF-W and OTF-S) in Cumbria in 2023, with and without a history of any TB incident in the previous 3 years.

Figure 3 description: Bar chart showing the number of herds with a TB incident, by OTF-W and OTF-S, in 2023 with and without a history of TB in the last 3 years. Herds with no history in the last 3 years are shown in blue, and those with a history of TB in the last 3 years are shown in green. Eight herds with OTF-S incidents had no history, and one herd with an OTF-S incident had history of TB in the last 3 years. Seven herds with OTF-W incidents had no history, and one herd with an OTF-W incident had history of TB in the last 3 years.

Overall recurrence

In 2023, 41% of incidents detected across the region were in herds with a history of TB at any point in the herd’s lifetime, including more than 3 years previously (3 out of 9 OTF-S and 4 out of 8 OTF-W), as shown in Figure 4.

Overall recurrence of TB was unchanged compared to 2022 (41%, 7 out of 15 OTF-S and 2 out of 7 OTF-W).

TB Incident	No history of TB within the herd lifetime	History of TB within the herd lifetime
OTF-S	6	3
OTF-W	4	4

Figure 4: Number of herds with a TB incident (by OTF-W and OTF-S) in Cumbria in 2023, with and without a history of any TB incident in the herd’s lifetime.

Figure 4 description: Bar chart showing the number of herds with a TB incident, by OTF-W and OTF-S, in 2023 with and without a history of TB in ever. Herds with no history of TB are shown in blue, and those with a history of TB at any point in time are shown in green. Six herds with OTF-S incidents had no history, and 3 herds with an OTF-S incident had history of TB at any point in time. Four herds with OTF-W incidents had no history, and 4 herds with an OTF-W incident had history of TB at any point in time.

Geographical distribution of TB incidents

All but 5 of the 17 new TB incidents detected in Cumbria during 2023 were in the eastern half of the county. Of these, the OTF-W incidents occurred along the Eden Valley to the north-east of Penrith, within HS29. Most of the OTF-S incidents were found to the south and east of Penrith, in and around HS21. One OTF-S incident was found to the south of the Lake District National Park. The remaining 5 incidents were distributed across the north-west of the county. This is shown in Figure 5.

Whole Genome Sequencing (WGS) replaced genotyping at APHA in 2021. There were 5 new OTF-W incidents associated with clade B3-11 of M. bovis, which has a homerange across much of the North Midlands, extending up into Greater Manchester. All 5 of those B3-11 incidents were in the Eden Valley area where HS29 has been established (Figure 5). One OTF-S incident was also detected in this area.

An OTF-W incident with clade B6-62 was detected to the West of Carlisle. B6-62 is predominantly found in the southern Edge Area from Warwickshire down to Wiltshire and north-west Hampshire.

One OTF-W incident was caused by infection with clade B6-51 of M. bovis, to the west of Wigton. As described above, this is a relatively novel clade in GB. In this same area, 2 OTF-S incidents were reported, increasing the overall numbers for that area to higher than previous years. The area is being kept under review. To the south of Cockermouth (West Cumbria), one OTF-W incident, which subsequently yielded a negative culture was recorded in 2023.

Figure 5: Location of cattle holdings in Cumbria with new TB incidents (OTF-W and OTF-S) in 2023, and cattle holdings with pre-2023 OTF-W incidents still ongoing at the beginning of 2023, overlaid on a cattle density map. Note that ‘OTF-W Introduced 2023’ refers to OTF-W incidents in which cattle movements were the most likely source of infection.

Figure 5 description: A map of Cumbria showing the cattle density, the geographical location of cattle holdings with new TB incidents (OTF-W and OTF-S) in 2023, and OTF-W incidents pre-2023. Dark blue areas represent higher cattle density and light blue represent lower cattle density. New OTF-W incidents detected in 2023 are shown as triangles and colour-coded based on the WGS clade that was detected in the incident. Pink triangles represent clade B3-11, blue triangles represent clade B6-51, red represents clade B6-84, and white triangles represent incidents where the WGS clade was undetermined. OTF-S incidents in 2023 are shown as circles. OTF-W incidents detected pre-2023 are shown as squares. The geographical location of potential TB hotspots are shown in orange and confirmed hotspots are brown. Most TB incidents in 2023 were located within the north-east of the county and are described in more detail in the main body of text.

As displayed in Figure 6, most OTF-W incidents in Cumbria in 2023 were attributed to exposure to infected wildlife. This was driven by the 5 OTF-W incidents within HS29.

The OTF-W incident west of Carlisle was likely attributed to the introduction of undetected infected cattle. As mentioned above, the source of the explosive OTF-W incident west of Wigton remains obscure, following isolation of the relatively novel clade B6-51 of M. bovis. A possible source of infection was direct or indirect contact with contiguous undisclosed infected imported cattle.

The OTF-W incident near Cockermouth was culture negative and had an obscure origin.

Figure 6: Map of the source of infection pathway recorded with the highest level of certainty, for OTF-W incidents, and the location of OTF-S incidents in Cumbria which started in 2023. Local cattle refer to residual infection and contiguous cattle risk pathways. Purchased refers to cattle movement risk pathways. Wildlife refers to both badger and other wildlife risk pathways.

Figure 6 description: A map of Cumbria showing the geographical location of cattle holdings with new OTF-W incidents in 2023 and the most likely source of infection. OTF-W incidents are shown as circles in different colours which represent the source of infection. Blue represents local cattle, brown represents purchased cattle, and green represents wildlife. New OTF-S incidents in 2023 are shown as triangles. The geographical location of potential TB hotspots are shown in orange and confirmed hotspots are brown. Most OTF-W incidents in 2023 had wildlife as the source of infection pathway with the highest level of certainty, with only one other attributed to purchased infection.

Figure 7 shows the hotspot areas and radial surveillance zones around OTF-W incidents that were active, completed or not instigated in Cumbria during 2023. OTF-W incidents in Cumbria have been more localised to the east of the county in recent years, mainly within HS29 and HS21. Unlike the previous 3 years, there were a number of new OTF-W incidents towards the west of the county. As such, there were 3 new active radial zones in the north-west area of Cumbria, as can be observed in Figure 7.

Figure 7: Hotspot areas and radial surveillance zones around OTF-W incidents that were active, completed or not instigated in Cumbria during 2023, by year of initiation.

Figure 7 description: A map of Cumbria showing the geographical location of hotspots and radial surveillance zones around OTF-W incidents in 2023. The radial zones are shown as circles. Active radial zones are shown as solid line circles, completed radial zones are shown as dotted line circles, and radial zones that were not instigated are shown as orange triangles. The colour of the circles represents the year in which the radial zone was instigated: 2023 is green, 2022 is blue, 2021 is pink and 2014 to 2020 is orange. The geographical location of potential TB hotspots are shown in orange and confirmed hotspots are brown. In 2023, there were 3 new active radial zones, located in the north-west area of Cumbria.

TB hotspots

There are 3 hotspots within Cumbria, 2 with M. bovis infection isolated from wildlife. APHA is continuing to test ‘found-dead’ badgers and deer carcasses reported through the Defra Rural Service Helpline (03000 200 301).

The total number of incidents reported in the TB hotspots in this report does not include negative slaughterhouse cases.

Hotspot 21

Confirmed Hotspot HS21 was established in 2016 following detection of a cluster of cattle incidents which had yielded B6-23 (17:z) isolates. Infection in local wildlife was identified in the spring of 2017 after the same clade was isolated from 3 ‘found-dead’ badger carcasses as part of wildlife surveillance carried out in hotspots.

There were 4 new OTF-S incidents but no new OTF-W incidents in HS21 in 2023 (Figure 8). The number of OTF-W incidents disclosed in HS21 has gradually declined since 2016.

There were no B6-23 cattle isolates identified within the hotspot in 2023 and the most recent cattle Incidents in HS21 to yield B6-23 occurred in 2018.

Badger disease control measures have been taking place in the area since 2018 and were carried out over the whole wildlife intervention area (Area 32 - Cumbria) for 2 years before a phased move to vaccination began in 2020 to reflect parts of the area having a lack of infection identified in the badger population. The whole area has been vaccinating since 2022, which continued in 2023. Further details about wildlife surveillance within hotspot areas can be found on the Bovine TB: hotspots in the Low Risk Area of England. Surveillance of road killed badgers and wild deer is still being carried out in this hotspot.

In 2020, cattle herds in the outer section of the hotspot became eligible to move to annual (instead of 6-monthly) TB surveillance testing, subject to certain eligibility criteria. In 2021 and 2022, the area within HS21 where this applies was extended to include more farms. Since October 2023, all farms in HS21 are eligible to move to annual testing, subject to certain eligibility criteria.

At the end of the year, there was one incident still open in this hotspot that began in 2022.

Year	OTF-S	OTF-W	Total
2016	2	6	8
2017	2	6	8
2018	2	3	5
2019	6	0	6
2020	4	2	6
2021	3	0	3
2022	3	1	4
2023	4	0	4

Figure 8: Annual number of new TB incidents in HS21, from 2016 to 2023.

Figure 8 description: Stacked bar chart showing the number of new OTF-W and OTF-S incidents detected in Confirmed Hotspot 21 between 2016 and 2023. OTF-W incidents are shown in green and OTF-S incidents are shown in blue. There were 4 new OTF-W incidents and no new OTF-S incidents in 2023, as described in the main body of text.

Hotspot 26

Potential Hotspot (HS26) was established in 2019, following a cluster of TB incidents in South Cumbria near Cartmel Fell, between Kendal and Windermere (Figure 7). The 3 OTF-W incidents triggering HS26 were all WGS clade B3-11 (formerly genotype 25: a). There have been no new incidents in HS26 since 2021.

Wildlife surveillance was implemented in the area in August 2019. However, only 7 submissions were suitable for PME and M. bovis was not identified. A summary of the wildlife carcasses collected for TB testing from Potential Hotspot Areas up to 18 January 2023 is available on GOV.UK. No enhanced TB control measures have been applied to cattle herds in HS26 to date, apart from the radial testing zones triggered around the OTF-W incidents from 2019. Nevertheless, the area continues to be closely monitored for any further developments.

Since 2021, there have been no new OTF-W or OTF-S incidents in HS26 (Figure 9).

Year	OTF-S	OTF-W	Total
2016	1	0	1
2017	1	0	1
2018	2	1	3
2019	6	2	8
2020	3	0	3
2021	1	0	1
2022	0	0	0
2023	0	0	0

Figure 9: Annual number of new TB incidents in HS26, from 2016 to 2023.

Figure 9 description: Stacked bar chart showing the number of new OTF-W and OTF-S incidents detected in Potential Hotspot 26 between 2016 and 2023. OTF-W incidents are shown in green and OTF-S incidents are shown in blue. There were no new OTF-W incidents and no new OTF-S incidents in 2023, as described in the main body of text.

Hotspot 29

An increase in OTF-W incidents along the Eden Valley was detected in 2021. Additional OTF-W incidents were disclosed in 2022, leading to the establishment of Confirmed Hotspot 29 (HS29) at the beginning of 2023. Clade B3-11 was detected in the 4 incidents from 2021, which after further WGS were identified as being closely related. The 3 new OTF-W incidents in 2022 also yielded clade B3-11 and were genetically related to the M. bovis isolates from 2021. Geographical and phylogenetic evidence combined provide strong evidence of local spread.

There were 6 new TB incidents in HS29 in 2023, 5 OTF-W (B3-11) and one OTF-S, which is a decrease from 8 incidents in 2022 (4 OTF-W and 4 OTF-S), as shown in Figure 10. Discrepancies compared to reporting in previous years can be explained by a recent extension of the northern boundary and the inclusion of cases in the area where HS29 overlaps HS21. Cases in this overlap area had previously been recorded under HS21 only but are now recorded for HS29 also. Moving forwards, all cases in the overlap area will be recorded for both HS21 and HS29.

The clade B3-11 isolates from the 5 OTF-W cases were all found to be closely genetically related to each other and the isolates from the previous years. At the end of 2023, from total of 6 new cases, 3 OTFW and one OTF-S were resolved, and 2 OTF-W are still ongoing.

Enhanced TB cattle control measures have been introduced in HS29. All the cattle herds are subject to 6-monthly surveillance testing and compulsory pre-movement testing. The first round of testing was completed and the second was already underway at the time of writing this report. One of the enhanced TB control measures in place for cattle herds in HS29 is to apply whole herd movement restrictions when only inconclusive reactors (IRs) have been disclosed at a TB test.

From January until the end of 2023, a total of 6 deer and 32 badger carcasses have been submitted to APHA. Out of 6 deer carcasses, 4 were culture negative and 2 are pending. Regarding the badger carcasses, at the end of October 2023, one badger carcass had yielded an M. bovis isolate, which closely matched the cattle isolates from incidents in HS29. A further 17 culture results were negative and 7 are still pending. Read further details on wildlife surveillance in potential and confirmed TB hotspots the Low Risk Area.

At the end of the year, there were 2 cattle TB incidents still open in HS29.

For the 5 OTF-W incidents in HS29, exposure to infected wildlife was the likely source of infection. Wildlife sources can include badgers and deer.

Year	OTF-W	OTF-S	Total
2015	3	4	7
2016	1	3	4
2017	1	5	6
2018	0	2	2
2019	0	2	2
2020	1	0	1
2021	5	3	8
2022	4	4	8
2023	5	1	6

Figure 10: Annual number of new TB incidents in HS29, from 2015 to 2023.

Figure 10 description: Stacked bar chart showing the number of new OTF-W and OTF-S incidents detected in Confirmed Hotspot 29 between 2016 and 2023. OTF-W incidents are shown in blue and OTF-S incidents are shown in green. There were 5 new OTF-W incidents and one new OTF-S incident in 2023, as described in the main body of text.

Skin test reactors and interferon gamma test-positive animals removed

As presented in Figure 11, the number of TB test reactors removed for TB control purposes in Cumbria increased seven-fold compared to 2022 (from 38 to 270). Of the 270 cattle that were removed for TB control purposes in 2023, 128 were skin test reactors, an increase from the 28 removed in 2022. A further 142 were positive on the interferon gamma (IFN-γ) blood test, an increase from the 10 removed in 2022. The total number of TB test reactors removed in 2023 was similar to the previously recorded peak of 282 recorded in 2018 (comprising 225 IFN-γ blood test and 57 skin test reactors).

As described above, the explosive incident west of Wigton contributed significantly to the marked rise in TB test reactors detected in 2023. Over the course of this incident 76 skin test reactors and 45 IFN-γ test positive animals were removed. In addition to this, high numbers of skin and IFN-γ test reactors were disclosed in certain herds experiencing TB incidents in HS29.

Year	Skin test reactors	Interferon gamma reactors	Grand total
2019	77	113	190
2020	37	2	39
2021	37	69	106
2022	28	10	38
2023	128	142	270

Figure 11: Number of skin test reactors and interferon gamma (IFN-γ) test positive cattle removed by APHA for TB control reasons in Cumbria, from 2019 to 2023.

Figure 11 description: Stacked bar chart showing the number skin test reactors and interferon gamma test positive animals removed from herds between 2019 and 2023 in Cumbria. Skin test reactors are shown in blue and interferon gamma test positive animals shown in green. There were 128 skin test reactors and 142 interferon gamma test positive animals removed from herds in 2023, as described in the main body of text.

Main risk pathways and key drivers for TB infection

Evidence collected during APHA veterinary investigations into the source of infection within herds was used to inform this understanding. In 2023, 17 (100%) of new TB incidents in Cumbria received a preliminary or final APHA veterinary investigation to identify the source of infection.

It can be challenging to retrospectively establish the route of infection for a TB incident herd. Ideally this investigation includes a thorough on-farm investigation and scrutiny of routinely collected data, such as cattle movement records, and the results of WGS where available. Up to 3 hazards and risk pathways were selected for each incident investigated. Each of these potential sources were given a score that reflects the likelihood of that pathway being the true one, based on the available evidence.

Details of the protocol used for these investigations, and the subsequent methodology used to calculate the weighted contribution of the different suspected sources of M. bovis infection can be found in the explanatory supplement to the annual reports 2023.

The key drivers of the TB epidemic in Cumbria during 2023 were identified as follows:

• exposure to infected badgers
• movement of undetected infected cattle
• exposure to infected deer

Unlike 2022, exposure to probable infected wildlife was the main pathway of infection for cattle herds in 2023, with a weighted contribution of 56.1%, as provided by Appendix 3. All pathways and the weighted contributions are given in Table 5, Appendix 3. Potential exposure to infected badgers had a weighted contribution of 44.1%. This is over 4 times greater than in 2022 (11%) and more than double compared to 2021 (20%). Other infected wildlife, however, had a slightly lower weighted contribution compared to previous years, decreasing to 12.0 % in 2023 compared to 15% in 2022. The overall increase in incidents with risk pathways associated with exposure to infected wildlife is being driven by the epidemiology in HS29.

The movement of undetected infected cattle continued to be another important risk pathway. Compared to 2022, the weighted contribution increased by 2.5% in 2023 (from 15% to 18.5%). Cattle movements currently have a much lower weighted contribution than exposure to infected wildlife. The epidemiology in HS29 is driving this but it should be acknowledged that hotspots nearly always develop as a result of purchased infected cattle being brought into the area and then transmitting the disease to wildlife.

Other or unknown sources had a weighted contribution of 13.2% in 2023. This category is added to those incidents in which there was high uncertainty around the selected pathways as alluded to earlier in the report (view the explanatory supplement to the annual reports 2023 for methodology).

Forward look

Cumbria currently has 2 hotspots (HS21 and HS29) where evidence for wildlife involvement in the epidemiology of cattle TB incidents has been found. Regarding HS21, the policy of combined enhanced TB control measures in cattle and wildlife continue to be successful in reducing the incidence of disease. HS29 on the other hand is only just embarking on enhanced TB control measures for cattle herds, and wildlife control measures are under consideration. In both areas, biosecurity measures to reduce the possibility of direct and indirect contact between cattle and wildlife and also between neighbouring cattle are key to continued disease control.

APHA is continuing to test ‘found-dead’ badgers and deer carcasses reported through the Defra Rural Service Helpline (03000 200 301).

More broadly, purchase of undetected, infected cattle continues to present a significant risk to Cumbria. Introductions of cattle without due regard to the TB history of the herd of origin may result in single incidents or as alluded to above, may result in infection being transmitted from cattle into local wildlife resulting in establishment of new TB hotspots. Farmers in Cumbria, in addition to complying with the TB movement testing regulations, need to ensure that they take an informed approach to sourcing cattle. This could include taking advice from their private vets and using the ibTB interactive map.

Moving forwards, existing, as well as new clusters arising within the county, will be areas of particular focus. Importantly, TB control measures will be aimed at resolving herd incidents quickly and with the least impact on farm businesses as possible.

Appendix 1: cattle industry demographics

Table 1: Number of cattle herds by size category in Cumbria as of 31 December 2023 (RADAR data on the number of holdings in the report year)

Size of herds	Number of herds
Undetermined	24
1 to 50	984
51 to 100	502
101 to 200	553
201 to 350	349
351 to 500	166
Greater than 500	170
Total number of herds	2,748
Mean herd size	158
Median herd size	83

Table 2: Number (and percentage of total) of animals by breed purpose in Cumbria as of 31 December 2023

Breed purpose	Number (and percentage of total) cattle
Beef	215,359 (49%)
Dairy	199,771 (46%)
Dual purpose	18,346 (4%)
Unknown	19 (0.004%)
Total	433,495

Appendix 2: summary of headline cattle TB statistics

Table 3: Herd-level summary statistics for TB in cattle in Cumbria in 2023. (Sam data showing the number of herds flagged as active at the end of the report year)

Herd-level statistics	2021	2022	2023
(a) Total number of cattle herds live on Sam at the end of the reporting period	3,242	3,278	3,144
(b) Total number of cattle herds subject to annual TB testing (or more frequent) at the end of the reporting period (any reason)	399	485	511
(c) Total number of whole herd skin tests carried out at any time in the period	1,205	1,066	1,299
(d) Total number of OTF cattle herds having TB whole-herd tests during the period for any reason	947	883	1,073
(e) Total number of OTF cattle herds at the end of the report period (herds not under any type of TB movement restrictions)	3,201	3,232	3,120
(f) Total number of cattle herds that were not under restrictions due to an ongoing TB incident at the end of the report period	3,231	3,266	3,137
(g.1) Total number of new OTF-S TB incidents detected in cattle herds during the report period	11	15	9
(g.2) Total number of new OTF-W TB incidents detected in cattle herds during the report period	7	7	8
(h.1) Of the new OTF-W herd incidents, how many occurred in a holding affected by another OTF-W incident in the previous 3 years?	3	4	2
(h.2) Of the new OTF-W herd incidents, how many could be considered secondary to a primary incident based on current evidence?	0	0	5
(h.3) Of the new OTF-W herd incidents, how many were triggered by skin test reactors or twice-inconclusive reactors (2xIRs) at routine herd tests?	0	1	1
(h.4) Of the new OTF-W herd incidents, how many were triggered by skin test reactors or 2xIRs at other TB test types (such as forward and back-tracings, contiguous, check tests)?	7	6	7
(h.5) Of the new OTF-W herd incidents, how many were first detected through routine slaughterhouse TB surveillance?	1	2	1
(i.1) Number of new OTF-S incidents revealed by enhanced TB surveillance (radial testing) conducted around those OTF-W herds	4	4	2
(i.2) Number of new OTF-W incidents revealed by enhanced TB surveillance (radial testing) conducted around those OTF-W herds	4	3	4
(j) Number of OTF-W herds still open at the end of the period (including any ongoing OTF-W incidents that began in a previous reporting period)	3	6	5
(k) Number of OTF-W herds still open at the end of the period that were on a finishing unit	1	1	1
(l) New laboratory-confirmed incidents of M. bovis infection in non-bovine domestic species or captive deer detected during the report period (indicate host species involved)	0	0	0

Note (a) and (f) Cattle herd counts in Appendix 2 Table 3 and Appendix 1 Table 1 differ due to different data sources used. Appendix 1 Table 1 uses data from RADAR, while Appendix 2 Table 3 uses data from Sam.

Table 4: Animal-level summary statistics for TB in cattle in Cumbria during 2023.

Animal-level statistics (cattle)	2021	2022	2023
(a) Total number of cattle tested with tuberculin skin tests or additional IFN-γ blood tests in the period (animal tests)	204,784	185,133	224,909
(b.1) Reactors detected by tuberculin skin tests during the year	37	28	128
(b.2) Reactors detected by additional IFN-γ blood tests (skin-test negative or IR animals) during the year	69	10	142
(c) Reactors detected during year per incidents disclosed during year	5.89	1.73	15.88
(d) Reactors per 1,000 animal tests	0.52	0.21	1.20
(e.1) Additional animals slaughtered during the year for TB control reasons (dangerous contacts, including any first time IRs)	3	1	8
(e.2) Additional animals slaughtered during the year for TB control reasons (private slaughters)	2	2	0
(f) Slaughterhouse (SLH) cases (tuberculous carcasses) reported by the Food Standards Agency (FSA) during routine meat inspection	6	7	7
(g) SLH cases confirmed by M. bovis PCR testing or bacteriological culture	1	2	1

Note (c) Reactors detected during year per incidents disclosed during year, reactors may be from incidents disclosed in earlier years, as any found through testing during the report year count here.

Note (g) SLH cases confirmed by culture of M. bovis, not all cases reported are submitted for culture analysis. All cases reported are from any period prior to or during restrictions.

Appendix 3: suspected sources of M. bovis infection for all of the new OTF-W and OTF-S incidents identified in the report period

In 2023, 100% (17 incidents) of new TB incidents in Cumbria received a preliminary or final APHA veterinary investigation to identify the source of infection.

Each TB incident could have up to 3 potential risk pathways identified. Each risk pathway is given a score that reflects the likelihood of that pathway bringing TB into the herd. The score is recorded as either:

• definite (score 8)
• most likely (score 6)
• likely (score 4)
• possible (score 1)

The sources for each incident are weighted by the certainty ascribed. Any combination of definite, most likely, likely, or possible can contribute towards the overall picture for possible routes of introduction into a herd.

If the overall score for a herd is less than 6, then the score is made up to 6 using the ‘other or unknown source’ option. Buffering up to 6 in this way helps to reflect the uncertainty in assessments where only ‘likely’ or ‘possible’ sources are identified.

Table 5 combines the data from multiple herds and provides the proportion of pathways in which each source was identified, weighted by the certainty that each source caused the introduction of TB.

The output does not show the proportion of herds where each pathway was identified (this is skewed by the certainty calculation).

WGS of M. bovis isolates can be a powerful tool in identifying a likely source of infection, however WGS clades have not been determined for OTF-S herds. As a result of varying levels of uncertainty, only broad generalisations should be made from these data. A more detailed description of this methodology is provided in the explanatory supplement for the annual reports 2023.

Table 5: Suspected sources of M. bovis infection for the 17 new TB incidents that received a veterinary investigation in Cumbria in 2023.

Source of infection	Possible (1)	Likely (4)	Most likely (6)	Definite (8)	Weighted contribution
Badgers	4	7	5	0	44.1%
Cattle movements	1	2	3	0	18.5%
Contiguous	6	1	0	0	8.3%
Residual cattle infection	1	1	0	0	3.3%
Domestic animals	0	0	0	0	0.0%
Non-specific reactor	0	0	0	0	0.0%
Fomites	1	0	0	0	0.7%
Other wildlife	6	2	0	0	12.0%
Other or unknown source	1	0	0	0	13.2%

Please note each TB incident could have up to 3 potential pathways so totals may not equate to the number of actual incidents that have occurred.