Research and analysis

North West of England (low risk area) year end report 2021

Updated 16 February 2023

Introduction

The Low Risk Area (LRA) was established in 2013. In 2014 this area was incorporated into the UK government’s strategy to achieve Officially Tuberculosis-Free (OTF) status for England by 2038. A key action was to recognise the different levels of bovine tuberculosis (TB) in different parts of the country and to vary the approach to control accordingly. Overall, the LRA has a very low and stable incidence of infected herds. The current strategy seeks to rapidly control infection when it arises through:

• high sensitivity testing of affected herds
• temporarily enhanced local surveillance (radial and hotspot testing)
• mandatory pre- and post-movement testing of cattle entering the LRA from higher risk areas of the UK

The aim 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 2021 in cattle herds in Greater Manchester, Lancashire, Merseyside, the counties that make up the North West region of the LRA.

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

This report is intended for individuals involved in the control of TB, both locally and nationally. This includes, but is not limited to farmers, veterinarians, policy makers and 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 2021.

Types of TB incident

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 This includes ‘Officially Tuberculosis-Free Status Withdrawn’ (OTF-W) incidents and ‘Officially Tuberculosis-Free Status Suspended’ (OTF-S) incidents.

OTF-W incidents are those involving one or more test reactors with typical lesions of TB identified at post-mortem meat inspection, or one or more animals with M. bovis-positive culture results from tissue samples collected from carcases during the PM inspection, or both.

OTF-S incidents are triggered by reactors to the Single Intradermal Comparative Cervical Tuberculin (SICCT) test, but without subsequent detection of TB lesions or positive culture results in any of those animals.

Cattle industry

Most cattle herds in the North West region are found in Lancashire. Cattle herds in Lancashire are mainly of the dairy type, whereas in Merseyside and Greater Manchester they are predominantly beef herds. Appendix 1 provides the number of cattle premises by size band and breed purpose for each county. There are 4 livestock markets in the region, all located in northern Lancashire. Two collection centres, both situated in Lancashire, handle slaughter cattle. There is one Licensed Finishing Unit (LFU), also located in Lancashire.

New TB incidents

New TB incidents in the North West region of the LRA nearly doubled between 2020 and 2021, from 13 to 24. There were 7 OTF-W incidents in 2021 (unchanged from 2020) and 17 OTF-S incidents (up from 6 in 2020) (Figure 1).

The biggest increase was in Lancashire, where 17 new TB incidents were reported in 2021. Both OTF-W and OTF-S incidents doubled in Lancashire compared to 2020; from 2 to 4 OTF-W and 6 to 13 OTF-S.

There were 7 new TB incidents in Greater Manchester in 2021 (3 OTF-W and 4 OTF-S), up from 5 in the previous year (all OTF-W). There have been no new TB incidents in Merseyside since 2018.

There were no incidents of TB reported in non-bovine species in the North West during 2021.

Figure 1: Annual number of new TB incidents in the North West of England, from 2016 to 2021.

In 2021, most new TB incidents in Lancashire were disclosed by routine herd tests (9 of 17, 53%). This is in contrast to 2020 when radial testing (RAD) disclosed the largest proportion of new incidents (4 of 8, 50%) (Figure 2).

Figure 2: Number of new TB incidents (OTF-W and OTF-S) in the North West of England in 2021 according to the surveillance method that detected them. Number of new incidents are given by county (no incidents disclosed in Merseyside).

County	Radial test (RAD)	Routine herd test (RHT)	Slaughterhouse test (SLH)	Traced bovine test (TR)	Whole herd test (WHT)	Post-movement test (POSTMT)	New herd test (NH)	Total
Greater Manchester	3	2	0	0	1	1	0	7
Lancashire	3	9	2	1	1	0	1	17

Consistent with previous years, most OTF-S incidents that ended in the North West in 2021 were quickly resolved in less than 150 days (Figure 3). Three OTF-W incidents closed in Lancashire in 2021. Two of these ended within 240 days of detection, and one incident within 550 days. In Greater Manchester, OTF-W incidents were resolved more quickly, with all 3 OTF-W incidents resolved within 240 days. There were no persistent incidents (those lasting more than 550 days) in the region.

Figure 3: Duration of all TB incidents (OTF-W and OTF-S) that ended in 2021, and the number of persistent TB incidents (lasting 551 days or more) that were unresolved at the end of 2021 in the North West of England. Note that LFUs have been excluded

Geographical distribution of TB incidents

Whole Genome Sequencing (WGS) replaced genotyping at APHA in 2021. Most new TB incidents in Lancashire continued to occur in areas of higher cattle density (Figure 4). Two OTF-W incidents (both due to infection with clade B3-11 of M. bovis) and 3 OTF-S TB incidents were disclosed in the east of Lancashire near Burnley, where the cattle density is comparatively lower. Three OTF-S incidents were also reported in this eastern area in 2020.

Figure 4: Location of cattle holdings in the north-west of England with new TB incidents (OTF-W and OTF-S) in 2021, and cattle holdings with pre-2021 OTF-W incidents still ongoing at the beginning of 2021, overlaid on a cattle density map. Note that ‘OTF-W Introduced 2021’ refers to OTF-W incidents in which cattle movements were the most likely source of infection.

Of the 2 2021 OTF-W incidents associated with clade B3-11 of M. bovis in the east of the county, only one received an Animal and Plant Health Agency (APHA) veterinary investigation into the likely source of infection. Cattle movements from the LRA and infected wild deer were both identified as likely risk pathways, while a fomite source was a possibility (Figure 5).

Figure 5: 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 West of England which started in 2021. 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.

Two OTF-W incidents were reported in the higher cattle density area of central Lancashire. One was associated with a rare clade of M. bovis (B6-84), and the other was caused by clade B6-62 (homerange in Oxfordshire and adjacent counties). There was a high degree of uncertainty around the source of infection for both herds.

In 2021, 2 new incidents (one OTF-W and one OTF-S incidents) occurred in the Stockport area of Greater Manchester along its south-east border with the Edge Area counties of Cheshire and Derbyshire. Radial areas instigated along this border since 2012 can be seen in Figure 6. Both the OTF-W incident (clade B6-11) and the OTF-S incident were disclosed by radial testing near Marple. Wildlife was identified as a likely source for the OTF-W incident. In the same area, one OTF-W (clade B3-11) was detected in 2020 and 3 OTF-W incidents were detected in 2019.

One OTF-W incident (clade B3-11) occurred in the north-west of Greater Manchester (Figure 4) and was likely linked to movements of infected cattle from the high risk area. The other OTF-W incident (also clade B3-11), north-east of Manchester near Oldham, was identified by radial testing around an earlier (2020) OTF-W incident (Figure 6). Both the 2020 and 2021 incidents were assessed as having a likely wildlife source as no other likely sources of infection were identified (Figure 5).

Figure 6: Potential hotspot areas and radial surveillance zones around OTF-W incidents that were active, completed or not instigated in the North West of England during 2021, by year of initiation.

Potential or confirmed TB hotspot areas

Potential Hotspot Area HS27

Potential TB hotspot HS27 straddles Lancashire and north Yorkshire and can be seen in Figure 6. This potential hotspot was established in January 2020 and is described in more detail in the 2020 Yorkshire and Humberside Epidemiological Report. There were no new OTF-W incidents or active radial zones in this area in 2021. Only one new OTF-S TB incident was detected in the Lancashire part of potential HS27, in a suckler beef herd with only 3 cattle.

Since its implementation, only one wild deer carcase has been submitted to APHA for examination, with negative culture results for M. bovis.

Main risk pathways and key drivers for TB infection

The main risk pathways and key drivers for TB infection within the North West in 2021 are considered here. Evidence collected during APHA veterinary investigations into the source of infection within herds was used to inform this understanding. In 2021, 18 of 24 (75%) of new TB incidents in the North West 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 2021.

The key drivers of the TB epidemic in the North West during 2021 were identified as follows:

• purchase of undetected infected cattle
• exposure to probable infected wildlife
• non-specific reactions to the tuberculin skin test

Movement of undetected infected cattle into the herd appears to be the main pathway of infection for cattle herds. As can be seen in Appendix 3, this pathway had an overall weighted contribution of 17%.

Wildlife, including badgers (12%) and non-badgers (14%) were also selected as a potential source of infection for some new TB incidents in 2021.

Finally, non-specific reactions to the tuberculin skin test were also identified as a driver for TB incidents (12%).

There was a high degree of uncertainty around the source of new incidents in the north-west in 2021. Other or unknown sources had a weighted contribution of 40%. This category is added to those incidents for which there was high uncertainty around the selected pathways (see explanatory supplement for methodology).

Forward look

The increase in new TB incidents in both Lancashire and Greater Manchester are a concern, however the predominance of OTF-S incidents in the area suggest TB is being found early and reduces the risk of onward lateral spread. Furthermore, most of the OTF-S incidents were resolved swiftly, in under 150 days.

As mentioned previously, the North West has a historically low level of TB, but the south-east area around Stockport and Manchester Airport is of concern due to its proximity to the Cheshire Edge Area. Furthermore, areas around Oldham in Greater Manchester and Burnley in Lancashire will require careful monitoring in case the situation deteriorates further in these areas in the future.

Appendix 1: Cattle industry demographics

Table 1: Number of cattle premises by size band in the North West of England at 1 January 2021, by county (RADAR data)

Size of herds	Number of herds in Greater Manchester	Number of herds in Lancashire	Number of herds in Merseyside
Undetermined	2	36	1
1-50	272	790	28
51-100	58	259	10
101-200	37	265	10
201-350	17	186	0
351-500	3	85	2
501+	1	93	3
Total number of herds	390	1,714	54
Mean herd size	54	132	92
Median herd size	24	56	47

Table 2: Number and percentage of total animals by breed purpose in the North West of England at 1 January 2021

Breed purpose	Number (and percentage of total) cattle in Greater Manchester	Number (and percentage of total) cattle in Lancashire	Number (and percentage of total) cattle in Merseyside
Beef	13,135 (62%)	79,440 (35%)	3,191 (64%)
Dairy	7,672 (36%)	132,764 (59%)	1,635 (33%)
Dual purpose	388 (2%)	13,857 (6%)	140 (3%)
Unknown	1 (0%)	1 (0%)	0
Total	21,196	226,062	4,966

Appendix 2: Summary of headline cattle TB statistics

Table 3: Herd-level summary statistics for TB in cattle in 2021

Herd-level statistics	Greater Manchester	Lancashire	Merseyside
(a) Total number of cattle herds live on Sam at the end of the reporting period	477	1,990	70
(b) Total number of cattle herds subject to annual TB testing (or more frequent) at the end of the reporting period (any reason)	109	297	7
(c) Total number of whole herd skin tests carried out at any time in the period	201	725	14
(d) Total number of OTF cattle herds having TB whole herd tests during the period for any reason	157	550	14
(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)	458	1,960	67
(f) Total number of cattle herds that were not under restrictions due to an ongoing TB incident at the end of the report period	475	1,986	70
(g.1) Total number of new OTF-S TB incidents detected in cattle herds during the report period	4	13	0
(g.2) Total number of new OTF-W TB incidents detected in cattle herds during the report period	3	4	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 three years?	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
(h.3) Of the new OTF-W herd incidents, how many were triggered by skin test reactors or 2x inconclusive reactors (IRs) at routine herd tests?	0	2	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)?	3	0	0
(h.5) Of the new OTF-W herd incidents, how many were first detected through routine slaughterhouse TB surveillance?	0	2	0
(i.1) Number of new OTF-S incidents revealed by enhanced TB surveillance (radial testing) conducted around those OTF-W herds	1	3	0
(i.2) Number of new OTF-W incidents revealed by enhanced TB surveillance (radial testing) conducted around those OTF-W herds	2	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)	2	2	0
(k) Number of OTF-W herds still open at the end of the period that are within a finishing unit	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

Table 4: Animal-level summary statistics for TB in cattle in 2021

Animal-level statistics (cattle)	Greater Manchester	Lancashire	Merseyside
(a) Total number of cattle tested in the period (animal tests)	14,533	116,412	1,777
(b.1) Reactors detected by tuberculin skin tests during the year	9	26	0
(b.2) Reactors detected by additional IFN-γ blood tests (skin-test negative or IR animals) during the year	20	23	0
(c) Reactors detected during year per incidents disclosed during year	4.14	2.88	0.00
(d) Reactors per 1,000 animal tests	2.00	0.42	0.00
(e.1) Additional animals slaughtered during the year for TB control reasons (dangerous contacts, including any first time IRs)	0	0	0
(e.2) Additional animals slaughtered during the year for TB control reasons (private slaughters)	0	2	0
(f) SLH cases (tuberculous carcases) reported by the Food Standards Agency (FSA) during routine meat inspection	2	4	0
(g) SLH cases confirmed by culture of M. bovis	0	2	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

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) or 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/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). Whole genome sequencing (WGS) of M. bovis isolates can be a powerful tool in identifying a likely source of infection, however WGS clades are not 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 2021.

Table 5: Suspected sources of M. bovis infection for all new OTF-W and OTF-S incidents identified in 2021

Source of infection	Possible (1)	Likely (4)	Most likely (6)	Definite (8)	Weighted contribution
Badgers	10	3	0	0	11.6%
Cattle movements	12	2	1	1	16.7%
Domestic animals	0	0	0	0	0.0%
Contiguous	3	1	0	0	4.3%
Residual cattle infection	0	0	0	0	0.0%
Non-specific reactor	1	2	2	0	12.1%
Fomites	2	0	0	0	1.0%
Other wildlife	8	3	1	0	13.5%
Other or unknown source	2	0	3	0	40.7%

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.