Spatial clustering of TB-infected cattle herds prior to and following proactive badger removal

Abstract

SUMMARYBovine tuberculosis (TB) is primarily a disease of cattle. In both Ireland and the UK, badgers (Meles meles) are an important wildlife reservoir of infection. This paper examined the hypothesis that TB is spatially correlated in cattle herds, established the range of correlation and the effect, if any, of proactive badger removal on this. We also re-analysed data from the Four Area Project in Ireland, a large-scale intervention study aimed at assessing the effect of proactive badger culling on bovine TB incidence in cattle herds, taking possible spatial correlation into account. We established that infected herds are spatially correlated (the scale of spatial correlation is presented), but at a scale that varies with time and in different areas. Spatial correlation persists following proactive badger removal.

Joint Spatio-Temporal Modeling of Mycobacterium bovis Infections in Badgers and Cattle – Results from the Irish Four Area Project

“…A sett is regarded as bTB positive if any badger captured in the sett was bTB positive. As stated in Kelly and More (2011), the culture method used underestimates the true infection prevalence. Badger setts are at best incompletely culled out via snare traps (Sleeman et al 2009) and thus the same sett may form part of the data for both stages 1 and 2.…”

“…A herd was designated infected in a year if it contained at least two cattle that tested positive for bTB in that annual yearly Single Intradermal Comparative Tuberculin Test (SICTT), as in Kelly and More (2011). This test has sensitivity 52.9-60.8% and specificity 99.2-99.8% of which further details can be found in Clegg et al (2011).…”

“…As a herd may be located on multiple parcels of land, GIS coordinates of the herd are taken as the centroid of the main parcel of land. The advantages and disadvantages of this choice is discussed in detail in Kelly and More (2011).…”

“…Kelly et al (2010) and Kelly and More (2011) found spatial correlation of the disease in badgers and cattle separately. Here the question of spatial association across the species is considered, to further the understanding of the spatial structure of the disease together with the role of underlying geography.…”

“…In previous spatial analyses related to bTB in cattle herds, Kelly and More (2011) restricted attention to isotropic spatial correlation, while Kelly (2011) and Kelly (2012) do account for possible anisotropy in different ways. In this study, anisotropic spatial correlation is considered using geometric anisotropic correlation structures not considered previously.…”