Detection of a local Mycobacterium bovis reservoir using cattle
surveillance data
Abstract
The incidence of bovine tuberculosis (TB, caused by Mycobacterium
bovis) in cattle has been associated with TB in badgers ( Meles
meles) in parts of England. The aim was to identify badger associated
M. bovis reservoirs in the Edge Area, between the High and Low
Risk Areas for cattle TB. Data from badger TB surveys were sparse.
Therefore, a definition for a local M. bovis reservoir
potentially shared by cattle and badgers was developed using cattle TB
surveillance data. The performance of the definition was estimated
through Latent Class Analysis using badger TB survey data. Spatial units
(25 km 2 ) in the Edge Area were classified as having
a reservoir if they had i) at least one OTF-W (Officially Tuberculosis
Free – Withdrawn) incident in a cattle herd not attributed to cattle
movement in the previous two years, ii) more OTF-W incidents than
Officially Tuberculosis Free – Suspended (OTF-S) incidents in the
previous two years and iii) at least one TB incident (OTF-S or OTF-W) in
at least three of the previous seven years. Approximately twenty percent
of the Edge Area was classified as having a local M. bovis
reservoir using the cattle-based definition. Assuming 15% TB prevalence
in Edge Area badgers, sensitivity for the local M. bovis
reservoir definition varied from 25.7% (95% Credible Interval (CrI)
10.7 to 85.1 %) to 64.8 % (95% CrI 48.1 to 88.0 %). Specificity was
91.9% (CrI 83.6 to 97.4 %). Over ninety percent of the local reservoir
was in stable endemic TB areas identified through previous work and its
spatial distribution was largely consistent with local veterinary
knowledge. Uncertainty in the reservoir spatial distribution was
explored through its recalculation in spatial units shifted in different
directions. We recommend that the definition is re-evaluated as further
data on badger infection with M. bovis becomes available.