Research and analysis

Isles of Scilly (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 on the Isles of Scilly, which is part 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 This includes ‘Officially Tuberculosis-Free Status Withdrawn’ (OTF-W) incidents and ‘Officially Tuberculosis-Free Status Suspended’ (OTF-S) incidents.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

The Isles of Scilly are a small archipelago situated 28 miles south-west of the Cornish peninsula. Five of the islands are populated and they have their own independent council. In 2021 there were 19 herds (using RADAR data, see Appendix 1) or 22 herds (using Sam data, see Appendix 2) registered, with 264 cattle between them. Figure 1 displays cattle density in the Isles of Scilly in 2021. There is a small amount of trade between the islands (designated Low Risk Area) and the Cornish mainland, which is part of the High Risk Area (HRA).

Figure 1: Cattle density in the Isles of Scilly in 2021

All cattle moving on from the mainland since 1 April 2016 have been eligible for post-movement TB testing and, as most travel from the HRA, they will have been subjected to pre-movement testing too.

The cattle herds on these islands are mostly very small. Appendix 1 shows that only one herd contains more than 50 cattle. This is a medium-sized beef herd of just under 100 cattle on the island of Tresco.

Small herd sizes minimise the likelihood of acquiring TB infection as size is known to be a major risk factor for TB. However, the largest mitigating factors are likely to be the previously clear TB history of all cattle herds, the relatively few movements on, and the lack of known wildlife reservoirs of M. bovis infection on the islands. Rats are ubiquitous on the islands and St Mary’s (the largest island) has many feral hedgehogs, but there are no deer, foxes, squirrels, badgers, or other mustelids present. Rabbits, mice and shrews are found on all the islands.

There are no livestock markets, abattoirs, or Licensed Finishing Units (LFUs) on the islands. Fat animals are transported by sea to abattoirs on the mainland. The 5 inhabited islands constitute 5 distinct epidemiological groups for disease purposes. There were 8 movements of 4 animals between islands in 2021. These were 2 breeding bulls and 2 yearlings. Over the same period there were 5 movements of 7 animals from 5 different source premises, all located in the HRA part of the mainland, onto the Scillies. All 5 of these source holdings were in Cornwall, but 3 of these animals came via Truro market. These were 2 calves and a bull.

New TB incidents

There were no TB incidents between 2014 and 2021.

Main risk pathways and key drivers for TB infection

The major risk to cattle herds on the Isles of Scilly are movements of cattle or other in-contact domestic species from the neighbouring HRA mainland. In 2021, there were 8 movements of 4 animals between islands. Over the same period there were 5 movements of 7 animals onto the islands from 5 different source premises in the HRA part of the mainland (compared with 7 animals from 5 HRA holdings in 2020). All the source holdings were in Cornwall. Three animals moved via Truro market. All cattle moved are subject to both pre- and post-movement testing requirements. The majority appear to be replacement breeding stock or breeding bulls.

There are no required movement records for camelids. Sheep, goat and pig movements have not been analysed for 2021, however, these species are not generally thought to be likely sources of infection for cattle.

Overall, the risk of TB introduction is low given the small number of cattle moving on and the mitigating factors of both pre- and post-movement testing.

Forward look

To date, controls appear to be very effective in preventing TB occurrence on the Isles of Scilly. Over the next two years it is highly likely that there will be no TB incidents on the Isles of Scilly. This is based on the previous history of at least 20 years of TB freedom, very few cattle movements and an absence of a wildlife reservoir.

The Isles of Scilly have already achieved the potential for OTF status.

Appendix 1: Cattle industry demographics

Table 1: Number of cattle premises by size band in the Isles of Scilly at 1 January 2021 (RADAR data).

Size of herds	Number of herds in Isles of Scilly
Undetermined	0
1-50	18
51-100	1
101-200	0
201-350	0
351-500	0
501+	0
Total number of herds	19
Mean herd size	14
Median herd size	8

Table 2: Number (and percentage of total) animals by breed purpose in the Isles of Scilly at 1 January 2021.

Breed purpose	Number (and percentage of total) cattle in Isles of Scilly
Beef	227 (85%)
Dairy	17 (6%)
Dual purpose	20 (7%)
Unknown	0
Total	264

Appendix 2: Summary of headline cattle TB statistics

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

Herd-level statistics	2019	2020	2021
(a) Total number of cattle herds live on Sam at the end of the reporting period	22	22	22
(b) Total number of cattle herds subject to annual TB testing (or more frequent) at the end of the reporting period (any reason)	0	0	0
(c) Total number of whole herd skin tests carried out at any time in the period	5	4	4
(d) Total number of OTF cattle herds having TB whole herd tests during the period for any reason	5	4	4
(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)	22	22	22
(f) Total number of cattle herds that were not under restrictions due to an ongoing TB incident at the end of the report period	22	22	22
(g.1) Total number of new OTF-S TB incidents detected in cattle herds during the report period	0	0	0
(g.2) Total number of new OTF-W TB incidents detected in cattle herds during the report period	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 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	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
(h.5) Of the new OTF-W herd incidents, how many were first detected through routine slaughterhouse TB surveillance?	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
(i.2) Number of new OTF-W incidents revealed by enhanced TB surveillance (radial testing) conducted around those OTF-W herds	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)	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
(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)	2019	2020	2021
(a) Total number of cattle tested in the period (animal tests)	54	55	46
(b.1) Reactors detected by tuberculin skin tests during the year	0	0	0
(b.2) Reactors detected by additional IFN-γ blood tests (skin-test negative or IR animals) during the year	0	0	0
(c) Reactors detected during year per incidents disclosed during year	0	0	0
(d) Reactors per 1,000 animal tests	0	0	0
(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	0	0
(f) SLH cases (tuberculous carcases) reported by the Food Standards Agency (FSA) during routine meat inspection	0	0	0
(g) SLH cases confirmed by culture of M. bovis	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.