Guest Editorial Tuberculosis in deer: Another piece in the unfinished Mycobacterium bovis jigsaw In this issue of The Veterinary Journal, findings from the histopathological examination of lymph node and lung le- sions from deer that were positive on culture for Mycobac- terium bovis are detailed (Johnson et al., 2008). The samples from 57 deer collected over a 5 year period were mainly from South-West England, which formed part of a wild mammal survey. Perhaps not surprisingly, the vast majority of lesions were at an advanced state of develop- ment, which may reflect a sampling bias in the collection of the specimens (Griffin and MacKintosh, 2000). In con- trast with the infection in cattle, lesions resembled ab- scesses more than granulomata with the majority (67%) showing large numbers of bacilli. Assessment of the lesions suggested that two-thirds of these deer had a high probabil- ity of being able to excrete M. bovis thereby enabling the possibility of aerosolised transmission of the infection. Estimates of the prevalence of tuberculous lesions in deer within the British Isles vary and, as with measurement in any wild species, may be highly inaccurate. However, the preva- lence of tuberculous lesions in deer is thought to be less than 5% (Clifton-Hadley and Wilesmith, 1991; Abernethy et al., 2006; Delahay et al., 2007). Moreover, the infection can be clustered and may show a high prevalence (>20%) in some groups of deer, both in parkland and wild deer (Stuart et al., 1988; D.A. Abernethy, personal communication). Combining the above information would tend to lead one to the conclusion that tuberculosis in deer is not that uncommon and that at the very least a certain proportion of infected deer can excrete large numbers of tuberculous bacilli via the respiratory system. Thus, in theory, deer could be considered to have the potential to seed infection into the cattle population. For this to occur there must be overlap in the spatial distribution of deer and cattle as well as the possibility for interaction between the two that is conducive to transmission of M. bovis by one of the avail- able routes (Corner, 2006). White tailed deer have been implicated with the re-emer- gence of tuberculosis in cattle in Michigan, USA. An in- crease in the deer population, partly assisted by winter supplemental feeding, has been proposed as the main factor contributing to the increased prevalence of tubercu- losis in the deer with subsequent spill over to the cattle pop- ulation (Corner, 2006). However, the transmission process is unclear and the inter-species infection rates are consid- ered as rare events (32 outbreaks in cattle over 8 years in 548 herds). The paper by Johnson et al., (2008) lends some more data to the unfinished jigsaw that forms the ecology of M. bovis in Great Britain. Although the sample size is rel- atively small and the study mostly validates what has been documented elsewhere, the article does keep open the de- bate on the role of deer in the epidemiology of tuberculosis. However, as highlighted by the report of the Independent Scientific Group on cattle tuberculosis (Anon, 2007), con- trol of this infection within a feral reservoir is costly and the main focus must clearly be directed towards enhanced measures in relation to its control in cattle. Fraser Menzies Veterinary Epidemiology Unit, Department of Agriculture and Rural Development, Dundonald House, Belfast, BT4 3SB Northern Ireland, UK Tel.: +44 28 9052 4376; fax: +44 28 9052 5281 E-mail address: fraser.menzies@dardni.gov.uk References Abernethy, D.A., Denny, G.O., Menzies, F.D., McGuckian, P., Honold, N., Roberts, A.R., 2006. The Northern Ireland programme for the control and eradication of Mycobacterium bovis. Veterinary Microbi- ology 112, 231–237. Anon., 2007. Bovine TB: the scientific evidence. Final Report of the Independent Scientific Group on cattle TB. Department for Environ- ment, Food and Rural Affairs. 289 pp. Clifton-Hadley, R.S., Wilesmith, J.W., 1991. Tuberculosis in deer: a review. Veterinary Record 129, 5–12. Corner, L.A.L., 2006. The role of wild animal populations in the epidemiology of tuberculosis in domestic animals: how to assess the risk. Veterinary Microbiology 112, 303–312. www.elsevier.com/locate/tvjl The Veterinary Journal 175 (2008) 287–288 The Veterinary Journal 1090-0233/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.tvjl.2007.07.021