Research and analysis

Isles of Scilly (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 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 Isles of Scilly, which is part of the LRA. None of the new TB incidents detected in 2023 were disclosed in the Isles of Scilly.

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 This includes both ‘Officially Tuberculosis-Free Status Withdrawn’ (OTF-W) and ‘Officially Tuberculosis-Free Status Suspended’ (OTF-S) incidents.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

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 2023, there were 18 herds (using RADAR data, see Appendix 1) or 21 herds (using Sam data, see Appendix 2) registered, with 234 (mainly beef) cattle between them. Figure 1 displays cattle numbers in the Isles of Scilly in 2023. Of the 234 cattle registered in the Isles of Scilly, 67 were on St Mary’s.

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 population (animals) in the Isles of Scilly in 2023.

Figure 1 description: Map of the Isles of Scilly, showing the names of the 5 main islands and the number of cattle on each island in 2023. The cattle density is shown by blue circles, smaller circles representing less cattle and larger circles representing a higher number of cattle. In 2023, most cattle were on Tresco, followed by St Mary’s, Bryher, St Agnes, and St Martin’s.

All cattle moving onto the islands from the mainland since 1 April 2016 have been subject to mandatory post-movement TB testing and, as most travel from the HRA, they will have also been TB tested with negative results in the 60 days before shipment to the islands.

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 large herd 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 inward movements of cattle, 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.

New TB incidents

There were no new TB incidents between 2014 and 2023. The headline cattle TB statistics for the Isles of Scilly are summarised in Appendix 2.

Main risk pathways and key drivers for TB infection

The major risk to cattle herds on the Isles of Scilly are movements of undetected cattle infected with Mycobacterium bovis, or other TB-susceptible domestic species from the neighbouring HRA mainland.

In 2023, there were 12 movements of 7 animals between the islands. These were 3 breeding bulls, 2 beef heifers and 2 calves.

Over the same period there were 6 movements of 16 animals onto the islands from 6 different source premises in the HRA of the mainland (compared with 5 animals from 3 HRA holdings in 2022). All 6 of the source holdings were in Cornwall. These movements comprised 4 beef cows with 3 calves at foot, 6 beef heifers, one dairy cow, one beef steer and one beef bull which subsequently returned to the mainland as did 2 of the calves at foot. All cattle remaining on the islands have undergone post-movement skin testing for TB with negative results, although 2 of the calves at foot (which returned to Cornwall) were not post-movement tested.

Over the same period, 11 cattle reared on the Isles of Scilly moved directly to slaughter on the mainland, providing some level of passive surveillance to supplement the tuberculin skin testing of approximately one quarter of all the herds every year.

Official movement records are not required for camelids. Sheep, goat and pig movements have not been analysed for 2023, 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 2 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.