The effects of bovine tuberculosis (Mycobacterium bovis) on mortality in a badger (Meles meles) population in England D. Wilkinson 1 , G. C. Smith 1 *, R. J. Delahay 1 , L. M. Rogers 1 , C. L. Cheeseman 1 and R. S. Clifton-Hadley 2 1 Central Science Laboratory, Sand Hutton, York YO41 1LZ, U.K. 2 Veterinary Laboratory Agency, New Haw, Addlestone KT15 3NB, Surrey, U.K. (Accepted 11 May 1999) Abstract The mortality rates of badgers Meles meles were estimated, using data from a long-term capture±mark± recapture study of an undisturbed badger population in south-west England. Two life table methods were used: fusion and discounting. Badgers were allocated to a particular TB status for all or part of their lives according to their degree of infection with bovine tuberculosis Mycobacterium bovis. Separate life tables were created for animals with each TB status, and for males and females, and the estimated mortality rates were compared statistically. The progression of M. bovis infection, and the positions of M. bovis lesions were also analysed. The main ®ndings are: (a) uninfected male badgers have a signi®cantly higher mortality rate than uninfected females, (b) infected badgers which are not excreting M. bovis do not have a signi®cantly higher mortality rate than uninfected badgers, (c) badgers which are excreting M. bovis have a much higher mortality rate than uninfected badgers, (d) male badgers appear to cope with M. bovis infection less well than females, and (e) there may be sex differences in the mode of spread of M. bovis in badgers. Key words: badger, Meles meles, mortality, bovine tuberculosis INTRODUCTION The Eurasian badger Meles meles is implicated in the spread of bovine tuberculosis (TB ± caused by Mycobac- terium bovis) to cattle in the U.K. (Muirhead, Gallagher & Burn, 1974; Nolan & Wilesmith, 1994). In the U.K. the number of cattle herds that have been diagnosed as positive for M. bovis has increased dramatically since 1992 (MAFF, 1993, 1994, 1995, 1996, 1997). The exact route of infection from badgers to cattle has not been determined, but is likely to be the result of cattle contacting contaminated badger sputum, urine or faeces (Muirhead et al., 1974; Brown, Cheeseman & Harris, 1992; Nolan & Wilesmith, 1994). At Woodchester Park, Gloucestershire, a naturally infected population of badgers has been studied since 1977. Since 1981 the M. bovis infection status of each badger trapped has been determined (a) by an ELISA antibody test (Goodger et al., 1994; Clifton-Hadley, Sayers & Stock, 1995) and (b) by culture of excretory products (Little, Naylor & Wilesmith, 1982; Cheeseman, Wilesmith, Stuart et al., 1988). This study population has one of the highest ever recorded densities of badgers (Rogers, Cheeseman et al., 1997). The transmission and maintenance of M. bovis within the badger population is complex. Badgers are social animals and usually live in groups with de®ned terri- tories (Kruuk, 1978; Cheeseman, Jones et al., 1981). Within-group transmission rates are therefore likely to be much higher than between-group disease transmis- sion. Moreover, four TB health states have been recognized which includes a state of intermittent bacterial excretion (Smith, Richards et al., 1995). Numerous models have now been created to simulate the epidemiology/disease dynamics of M. bovis in badgers (Anderson & Trewhella, 1985; Bentil & Murray, 1993; Smith, Richards et al., 1995; White & Harris, 1995; Ruxton, 1996; Smith, Cheeseman & Clifton-Hadley, 1997; Swinton et al., 1997). All these models have assumed that M. bovis infection has a detrimental effect on the individual badger which results in an increased mortality rate for infected animals. However, there has been no thorough analysis of the mortality rates of diseased badgers. The present study uses life tables to produce mortality estimates for uninfected and infected badgers of both sexes. A discounting life table is presented and used to improve the life table estimates. The likely consequences for epidemiological models of M. bovis in naturally infected badger populations is discussed. *All correspondence to: G. Smith. E-mail: g.smith@csl.gov.uk J. Zool., Lond. (2000) 250, 389±395 # 2000 The Zoological Society of London Printed in the United Kingdom