Research and analysis

North East of England (Low Risk Area) year end report 2023

Updated 24 October 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 Polymerase Chain Reaction (PCR) 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 the North East of England, which is part of the LRA. In 2023, 2% of all new TB incidents in the LRA were detected in the North East of England.

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 culture results in any of those animals.

Cattle industry

The cattle industry in the North East of England is predominantly beef-based. Cattle herd sizes vary between counties, as shown in Appendix 1, with over 90% of the region’s cattle located in Northumberland and County Durham. Breeding (beef) suckler herds account for most of the cattle population. However, there are also many finishing herds which rely on the continuous supply of store cattle sourced locally and from farms outside the region, such as those in the High Risk and Edge Areas of England, in Wales, and in Northern Ireland.

There are 7 livestock markets in the region. The biggest one is Darlington Market in County Durham, which holds both ‘green’ (regular) and ‘red’ (TB dedicated slaughter gathering) status cattle sales. It is the main slaughter market for fattening herds and holds slaughter gatherings accepting cattle from TB-restricted holdings, which are destined for slaughterhouses. The main market in Northumberland is Hexham Market, which holds ‘green’ sales only, including sales for slaughter cattle from Officially TB Free (OTF) herds.

There are 7 Licensed Finishing Units (LFUs), all of which are in County Durham. These units are licensed by the Animal and Plant Health Agency (APHA) and require their cattle to be housed all the time. Conditions of approval include demonstration of strict biosecurity protocols and wildlife proofing of the unit. Cattle in LFUs must be sourced from unrestricted (Officially TB Free) herds and subject to pre-movement TB testing when required but are exempt from post-movement or tracing testing.

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.

The traditional farming practice in the North East of England is for cattle to graze from April to late October and then to be housed over the winter months. There are some parcels of common grazing land and, if any TB incidents occur in herds using these areas, it can result in additional tracing activity.

New TB incidents

The number of new TB incidents detected in the North East of England in 2023 was the same as 2022 (3 incidents). Total incident numbers have been decreasing from a high of 10 in 2020, as shown in Figure 1a and b. There was one new OTF-W incident (unchanged from 2022 and 2021) and 2 new OTF-S incidents (the same as 2022, and one less from 2021). The geographic distribution of these incidents across the region was as follows:

• Northumberland reported one new OTF-W and one OTF-S incident in 2023, which was an increase from no incidents reported in 2022
• Durham reported one OTF-S incident in 2023 and no OTF-W incidents. This was unchanged from the previous year
• Cleveland reported no new TB incidents in 2023, which was down from one OTF-W and one OTF-S incident reported in 2022
• Tyne and Wear has reported no TB incidents since the 1990s (and hence this county is not shown in Figure 1a and b)

Cleveland

Year	OTF-W	OTF-S	Total
2014	0	0	0
2015	0	0	0
2016	0	0	0
2017	0	1	1
2018	0	0	0
2019	0	0	0
2020	2	0	2
2021	0	0	0
2022	1	1	2
2023	0	0	0

Durham

Year	OTF-W	OTF-S	Total
2014	3	0	3
2015	1	0	1
2016	2	2	4
2017	2	1	3
2018	0	1	1
2019	0	0	0
2020	0	1	1
2021	0	1	1
2022	0	1	1
2023	0	1	1

Figure 1a: Annual number of new TB incidents in the Cleveland and Durham, from 2014 to 2023.

Figure 1a description: Stacked bar chart showing the number of new OTF-W and OTF-S incidents detected in Cleveland and Durham between 2014 and 2023. OTF-W incidents are shown in blue and OTF-S incidents are shown in green. There were no new OTF-W or OTF-S incidents in Cleveland and one new OTF-S incident in Durham in 2023, as described in the main body of text.

Northumberland

Year	OTF-W	OTF-S	Total
2014	1	0	1
2015	0	2	2
2016	1	3	4
2017	0	2	2
2018	0	3	3
2019	1	5	6
2020	1	6	7
2021	1	2	3
2022	0	0	0
2023	1	1	2

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

Figure 1b description: Stacked bar chart showing the number of new OTF-W and OTF-S incidents detected in Northumberland between 2014 and 2023. OTF-W incidents are shown in blue and OTF-S incidents are shown in green. There was one new OTF-W incident and one new OTF-S incident 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

As displayed in Figure 2, the one new TB incident in Durham was detected by 4-yearly routine herd testing (RHT). Of the 2 new incidents in Northumberland, one was detected by RHT and the other by a 12-month post-incident test (12M) following resolution of a previous TB incident.

Location	12M Test	Routine Herd Test	Grand total
Durham	0	1	1
Northumberland	1	1	2

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

Figure 2 description: Bar chart showing which tests detected the new TB incidents in Durham and Northumberland in 2023. Two incidents were detected by routine herd testing, one in Durham and one in Northumberland, and one incident by 12-month testing in Northumberland.

The headline cattle TB statistics for the North East are summarised in Appendix 2.

Duration of TB incidents

A total of 2 TB incidents were resolved during 2023. Of these incidents, both started in 2023 and were resolved quickly within 100 days.

There were no persistent incidents (under movement restrictions for more than 550 days) in the North East. The new OTF-W incident that began in 2023 was still ongoing at the end of the year.

Unusual TB incidents

There were no TB incidents that could be considered unusual in the North East region in 2023.

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 the North East region in 2023. There were no confirmed or suspected cases of zoonotic (human) M. bovis infection found either.

Recurring TB incidents

The recurrence proportions are influenced by the small number of incidents (n=3), so any inter-year changes should be interpreted with caution.

Three-year recurrence

In the North East, one of 2 herds with a new OTF-S TB incident in 2023 had experienced another TB incident in the last 3 years. There were no OTF-W incidents in herds with a history of TB in the last 3 years.

Overall recurrence

In 2023, 33% of incidents reported across the region were in herds with a history of TB at any time, including more than 3 years previously (1 out of 2 OTF-S and 0 out of 1 OTF-W). The re-occurrence of TB incidents in herds in 2023 was 50% in Northumberland and 0% in Durham.

Overall recurrence of TB was unchanged compared to 2022 (33%, 0 out of 2 OTF-S and 1 out of 1 OTF-W).

Geographical distribution of TB incidents

In 2023, the new TB incidents were detected in herds located in the centre and west of the region (Figure 3).

In Northumberland, one OTF-W incident was detected in May 2023 with Whole Genome Sequencing (WGS) clade B6-84 in the west near the Cumbria border (Figure 3). This incident was detected in a 50-cattle beef sucker herd. The reactor animal was a 6-year-old cow born on the farm. This animal had visible lesions of TB at slaughter and was also culture positive. A supplementary interferon gamma (IFN-y) blood herd test disclosed another reactor, which had no visible lesions of TB at slaughter. Following 2 statutory short interval herd tests with negative results, the herd regained its OTF status in February 2024. After considering that there were no cattle movements onto this holding in the previous 5 years and no evidence of wildlife infection in the area or neighbouring farms, the origin of this incident is unknown.

One OTF-S incident was detected in the south of Northumberland towards the border with Tyne and Wear. This incident involved a 300-cattle dairy herd that rears its own replacements. This case was the third incident detected on this herd since 2020, all of them OTF-S. One reactor and 3 IRs were disclosed at 12M (post-incident) herd check test. The reactor animal had no visible lesions of TB at slaughter and was negative on culture and was not subject to PCR testing. The 3 IRs were clear in subsequent testing. After the compulsory short interval herd test, this herd regained its OTF status in April 2023. A possible source of infection seemed to be residual infection in the herd. Recently the 12-monthly testing carried out has been clear. Cattle movements was another possible risk pathway for this case.

The one OTF-S incident in Durham was disclosed in a 100-cattle beef fattening herd in the southwest of the county. One reactor was disclosed at a routine herd test (RHT). This animal had no visible lesions of TB at slaughter and was culture negative. The source of infection is possibly attributable to undetected infected cattle movements from the LRA. After one compulsory short interval test, this herd regained OTF status in April 2023.

There have been no new OTF-W incidents disclosed in Durham in recent years.

In Cleveland, unlike 2022, there were no new TB incidents recorded in 2023.

In Tyne and Wear, similarly to previous years, there were no new TB incidents recorded.

Figure 3: Location of cattle holdings in the North East 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 3 description: A map of the North East 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. Orange triangles represent clade B4-11, brown triangles represent clade B6-62, 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 TB hotspots are shown as ‘yellow lines’ (to be updated). The new OTF-W incidents in 2023 was located in the west of Northumberland and the OTF-S incident was in the southeast. The other OTF-S incident in Durham was located in the south and is described in more detail in main body of text.

The OTF-W incident in the west of Northumberland, near the Cumbria border, yielded a clade B6-84 isolate. Despite further investigation, the origin of this incident remains obscure (Figure 4).

Figure 4: 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 the North East 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 4 description: A map of the North East 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 TB hotspots are shown as ‘yellow lines’ (to be updated). The source of infection of the one OTF-W incident in 2023 was attributed to local cattle.

New OTF-W incidents of TB throughout the North East of England continue to arise very sporadically. The new OTF-W incident detected in the west of Northumberland triggered a radial zone in an area without a recent history of TB, as shown in Figure 5. One radial zone triggered in 2021 was still active in the east of Northumberland.

The 2022 OTF-W incident in Cleveland was the first incident in the southwest of the county for at least 10 years, and the radial zone was still active in 2023.

Figure 5: Hotspot areas and radial surveillance zones around OTF-W incidents that were active, completed or not instigated in the North East during 2023, by year of initiation.

Figure 5 description: A map of the North East 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 TB hotspots are shown as ‘yellow lines’ (to be updated). In 2023, there was one new active radial zone located in the west of Northumberland.

TB hotspots

There were no TB hotspot areas in any of the counties in the North East of England in 2023. Only one new radial zone was instigated in 2023 around the single OTF-W incident found to the west of Northumberland. There were 2 active radial zones (in Northumberland and Cleveland respectively) that were triggered in previous years, as shown in Figure 5.

Two OTF-W TB incidents that gave rise to radial zones in 2020 and 2021 were in close proximity, but as described above, it was concluded that these incidents were not related to one another following both APHA veterinary investigations and WGS analysis.

Skin test reactors and interferon gamma test-positive animals removed

As presented in Figure 6, the number of reactors removed for TB control purposes in the North East of England decreased in 2023 compared to 2022, from 12 to 4. Of the 4 cattle removed for TB control purposes in 2023, 3 were skin test reactors, up from 2 in 2021. A further one was positive on the IFN-γ test, down from 10 in 2022.

In Cleveland, there were no skin test reactors, compared to one skin test reactor in 2022. No IFN-γ tests were conducted in the region in 2023 as there were no OTF-W incidents and thus no herds were eligible for gamma testing.

In 2023, one skin test reactor was detected in Durham, which was the same number as in 2022. No IFN-γ tests were conducted in the region in 2023 either as there were no OTF-W incidents and thus no herds were eligible for gamma testing.

In Northumberland there was only one IFN-γ test positive animal, which was a decrease from 10 in 2022. There were 2 skin test reactors recorded, compared to none in 2022.

Cleveland

Year	Skin test reactors	Interferon gamma reactors	Total
2018	0	0	0
2019	0	0	0
2020	3	2	5
2021	0	5	5
2022	1	0	1
2023	0	0	0

Durham

Year	Skin test reactors	Interferon gamma reactors	Total
2018	1	0	1
2019	0	0	0
2020	1	0	1
2021	2	0	2
2022	1	0	1
2023	1	0	1

Northumberland

Year	Skin test reactors	Interferon gamma reactors	Total
2019	8	1	9
2020	11	17	28
2021	2	0	2
2022	0	10	10
2023	2	1	3

Figure 6: Number of skin test reactors and interferon gamma (IFN-γ) test positive cattle removed by APHA for TB control reasons in the North East, from 2019 to 2023.

Figure 6 description: Stacked bar chart showing the number skin test reactors and interferon gamma test positive animals removed from herds between 2019 and 2023 in the North East. Skin test reactors are shown in blue and interferon gamma test positive animals shown in green. There were no new skin test reactors or interferon gamma test positive animals removed from Cleveland in 2023. In Durham there was one skin test reactor and no interferon gamma test positive animals, and in Northumberland there were 2 skin test reactors and one interferon gamma test positive animal 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, all 3 (100%) new TB incidents in the North East of England 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.

Residual cattle infection was identified as being the highest weighted key driver of the TB incidents in the North East of England during 2023 (2 incidents, 22.2%). Cattle movements, contiguous cattle infection were also recorded as potential sources in other incidents in the North East in 2023, as shown in Appendix 3.

It should be noted that due to the small number of incidents, it is difficult to draw any firm conclusions for the aggregated data from veterinary investigations.

Two of the three incidents in the North East in 2023 were OTF-S and these always carry a higher level of uncertainty around the sources of infection as, by definition, the WGS clade of M. bovis could not be determined.

Higher uncertainty also exists where very small number of reactors are identified. Most of the incidents in 2023 presented no more reactors at subsequent testing and this provides some assurance that there is minimal lateral spread of infection within herds.

Forward look

The overall number of incidents remained the same in 2023, compared to 2022. The North East of England remains one of the LRA regions with the lowest incidence of TB in cattle. A low number of reactors are typically disclosed in each incident, and incidents have a relatively short duration. As a result, the impact of TB for farmers and the taxpayer was relatively low in the North East in 2023 in comparison with other areas of the country.

Timely detection and rapid removal of infected animals is one of the key steps in infectious disease control. This is likely to have played a significant role in the protection of the remaining susceptible cattle population and keeping the region relatively free of TB. It is therefore vital to maintain the passive and active TB surveillance within the LRA.

The consensus is that more local farmer meetings could help to increase awareness of TB. This should encourage careful sourcing of cattle and reduce the risk of introducing TB into the region by the movement of infected cattle from higher TB risk areas of the United Kingdom. It would be useful for farmers in the North East to be aware of the experiences of other LRA regions where inward movements of cattle from higher risk areas have resulted in the establishment of hotspots, for example in Cumbria. To further reduce TB incidence and maintain LRA status, enhanced TB surveillance measures need to be continued, together with the implementation of responsible cattle purchasing policies.

Given the history and the effectiveness of TB controls, it is very likely that the North East of England will continue to experience a very low number of sporadic TB incidents over the next few years. Given the objective of achieving TB OTF status for the whole of England by 2038, a focus is needed on the farming community’s attitude towards TB control and sourcing cattle to this area.

Appendix 1: cattle industry demographics

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

Size of herds	Number of herds in Cleveland	Number of herds in Durham	Number of herds in Northumberland	Number of herds in Tyne and Wear
Undetermined	1	8	4	0
1 to 50	49	389	301	23
51 to 100	25	158	179	14
101 to 200	26	124	191	12
201 to 350	9	64	117	6
351 to 500	5	23	41	1
Greater than 500	5	25	36	0
Total number of herds	120	791	869	56
Mean herd size	116	102	146	89
Median herd size	62	50	86	60

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

Breed purpose	Number (and percentage of total) cattle in Cleveland	Number (and percentage of total) cattle in Durham	Number (and percentage of total) cattle in Northumberland	Number (and percentage of total) cattle in Tyne and Wear
Beef	10,896 (78%)	69,254 (85%)	116,536 (91%)	4,257 (85%)
Dairy	2,917 (20%)	10,125 (12%)	9,181 (7%)	453 (9%)
Dual purpose	89 (0.6%)	1,334 (1%)	1,401 (1%)	247 (4%)
Unknown	24 (0%)	28 (0.035%)	15 (0.019%)	(0%)
Total	13,926	80,741	127,133	4,957

Appendix 2: summary of headline cattle TB statistics

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

Herd-level statistics	Northumberland	Durham	Cleveland	Tyne and Wear
(a) Total number of cattle herds live on Sam at the end of the reporting period	1,061	928	136	75
(b) Total number of cattle herds subject to annual TB testing (or more frequent) at the end of the reporting period (any reason)	33	11	14	1
(c) Total number of whole herd skin tests carried out at any time in the period	255	209	27	12
(d) Total number of OTF cattle herds having TB whole herd tests during the period for any reason	249	207	27	12
(e) Total number of OTF cattle herds at the end of the report period (herds not under any type of Notice Prohibiting the Movement of Bovine Animals (TB02) restrictions)	1,059	915	132	75
(f) Total number of cattle herds that were not under restrictions due to an ongoing TB incident at the end of the report period	1,060	928	136	75
(g.1) Total number of new OTF-S TB incidents detected in cattle herds during the report period	1	1	0	0
(g.2) Total number of new OTF-W TB incidents detected in cattle herds during the report period	1	0	0	0
(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?	1	0	0	0
(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	0	0
(h.3) Of the new OTF-W herd incidents, how many were triggered by skin test reactors or 2xIRs at routine herd tests?	1	0	0	0
(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)?	0	0	0	0
(h.5) Of the new OTF-W herd incidents, how many were first detected through routine slaughterhouse TB surveillance?	0	0	0	0
(i.1) Number of new OTF-S incidents revealed by enhanced TB surveillance (radial testing) conducted around those OTF-W herds	0	0	0	0
(i.2) Number of new OTF-W incidents revealed by enhanced TB surveillance (radial testing) conducted around those OTF-W herds	0	0	0	0
(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)	1	0	0	0
(k) Number of OTF-W herds still open at the end of the period that are within a finishing unit	0	0	0	0
(l) New confirmed (positive M. bovis culture) incidents in non-bovine species detected during the report period (indicate host species involved)	0	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 the North East during 2023.

Animal-level statistics (cattle)	Northumberland	Durham	Cleveland	Tyne and Wear
(a) Total number of cattle tested in the period (animal tests)	29,693	11,605	3,238	624
(b.1) Reactors detected by tuberculin skin tests during the year	2	1	0	0
(b.2) Reactors detected by additional IFN-γ blood tests (skin-test negative or IR animals) during the year	1	0	0	0
(c) Reactors detected during year per incidents disclosed during year	1.50	1.00	0.00	0.00
(d) Reactors per 1,000 animal tests	0.10	0.09	0.00	0.00
(e.1) Additional animals slaughtered during the year for TB control reasons (dangerous contacts, including any first time IRs)	0	0	0	0
(e.2) Additional animals slaughtered during the year for TB control reasons (private slaughters)	0	0	0	0
(f) SLH cases (tuberculous carcasses) reported by the Food Standards Agency (FSA) during routine meat inspection	1	0	0	0
(g) SLH cases confirmed by culture of M. bovis	0	0	0	0

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, all 3 (100%) new TB incidents in the North East 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 3 new TB incidents that received a veterinary investigation in the North East in 2023.

Source of infection	Possible (1)	Likely (4)	Most likely (6)	Definite (8)	Weighted contribution
Badgers	2	0	0	0	11.1%
Cattle movements	1	0	0	0	5.6%
Contiguous	1	0	0	0	5.6%
Residual cattle infection	0	1	0	0	22.2%
Domestic animals	0	0	0	0	0%
Non-specific reactor	0	0	0	0	0%
Fomites	0	0	0	0	0%
Other wildlife	0	0	0	0	0%
Other or unknown source	0	1	0	0	55.6%

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.