The results of further epidemiological studies of bovine spongiform encephalopathy (BSE) support the previous findings that the onset of exposure of the cattle population to a scrapie-like agent, sufficient to result in clinical disease, occurred in 1981/82. The onset of this exposure was related to the cessation, in all but two rendering plants, of the hydrocarbon solvent extraction of fat from meat and bone meal. A further possible explanation, related to the geographical variation in the reprocessing of greaves to produce meat and bone meal, was identified for the geographical variation in the incidence of BSE.

SUMMARYThis study investigates the course of tuberculosis in a naturally infected badger population, its impact on the population and the risk of spread to other species in the light of capture data and post-mortem findings from 47 tuberculous badgers, stratified by age group and sex, accrued since 1975. The findings are compared with those for 260 badgers from the same population in whom no evidence of infection was detected. Detailed estimates of seasonal variations in bodyweight for uninfected male and female cub, yearling and adult badgers are presented and compared to the weights at post-mortem examination of the tuberculous badgers, in whom poor condition and weight loss were the principal presenting signs. Lesions were seen especially in the lungs and associated lymph nodes, and in the kidneys. Organisms were detected intermittently in faeces, urine, sputum and discharging bite wounds. Infected animals could survive for nearly 2 years and produce cubs successfully.

T h e dynamics of bovine tuberculosis infection in a wild Badger population have been studied since 1981. Faeces are sampled regularly to determine the distribution of infection in the study area. Badgers in known infected social groups, plus the neighbouring groups, are periodically caught and subjected to full clinical and bacteriological examination to monitor the progression of infection within and between groups of Badgers. The interim results of this study are presented and discussed. During 5 years (1981)(1982)(1983)(1984)(1985), the temporal spread of infection between social groups in the study area was slow and restricted. Some clinically affected Badgers have survived for long periods. Evidence of infection in individual Badgers indicates that pseudo-vertical (mother to cub) transmission may be important in the maintenance of infection in the Badger population. There is also evidence of horizontal transmission by bite wounding and aerosol infection. Badger mortality due to Mycobacterium bovis infection was low, and the prevalence of infection in male Badgers is greater than in females. T h e data accumulated so far show no apparent relationship between Badger population density and the prevalence of M . bovis infection, nor is there any evidence to support the hypothesis that M . bovis infection acts to depress Badger population density significantly below diseasefree levels. Cattle and infected Badgers can co-exist for long periods without the disease necessarily being transmitted to cattle.

The data accumulated from 1972 to 1987 on the distribution and prevalence of tuberculosis in the badger population in Great Britain is reviewed. The current information on the influence of Mycobacterium bovis infection on badger population dynamics and its clinical effect on badgers is also summarized. The results of these reviews indicate that M. bovis is endemic in the British badger population and that the badger is an ideal maintenance host for M. bovis. The studies in progress to obtain a fuller understanding of the epidemiology of tuberculosis in badgers are also described.

Aims: The objective of these surveys was to estimate the prevalence of faecal carriage of Salmonella in healthy pigs, cattle and sheep at slaughter, and of pig carcase contamination with Salmonella. These data can be used as a baseline against which future change in Salmonella prevalence in these species at slaughter can be monitored. Methods and Results: In this first randomized National Survey for faecal carriage of Salmonella in slaughter pigs, cattle and sheep in Great Britain, 2509 pigs, 891 cattle and 973 sheep were sampled in 34 pig abattoirs and 117 red meat abattoirs in England, Scotland and Wales. Carriage of Salmonella in 25 g caecal contents was identified in 578 (23AE0% pigs) but in only 134 (5AE3%) of carcase swabs. The predominant Salmonella serovars found in both types of sample were S. Typhimurium (11AE1% caeca, 2AE1% carcases) and S. Derby (6AE3% caeca, 1AE6% carcases). The main definitive phage types (DT) of S. Typhimurium found were DT104 (21AE9% of caecal S. Typhimurium isolates), DT193 (18AE7%), untypable strains (17AE6%), DT208 (13AE3%) and U302 (13AE3%). Three isolates of S. Enteritidis (PTs 13A and 4) and one enrofloxacin-resistant S. Choleraesuis were also isolated. A positive Ômeat-juice ELISAÔ was obtained from 15AE2% of pigs at 40% optical density (O.D.) cut-off level and 35AE7% at 10% cut-off. There was poor correlation between positive ELISA results or carcase contamination and the caecal carriage of Salmonella. The ratio of carcase contamination to caecal carriage rates was highest in abattoirs from the midland region of England and in smaller abattoirs. In cattle and sheep 1 g samples of rectal faeces were tested. Two isolates (i.e. 0AE2%) were recovered from cattle, one each of S. Typhimurium, DT193 and DT12. One sheep sample (0AE1%) contained a Salmonella, S. Typhimurium DT41. In a small subsidiary validation exercise using 25 g of rectal faeces from 174 cattle samples, three (1AE7%) isolates of Salmonella (S. Typhimurium DT104, S. Agama, S. Derby) were found. Conclusions: The carriage rate of Salmonella in prime slaughter cattle and sheep in Great Britain was very low compared with pigs. This suggests that future control measures should be focused on reduction of Salmonella infection on pig farms and minimizing contamination of carcases at slaughter. Significance and Impact of the Study: This work has set baseline figures for Salmonella carriage in these species slaughtered for human consumption in Great Britain. These figures were collected in a representative way, which enables them to be used for monitoring trends and setting control targets.

Naturally occurring transmissible spongiform encephalopathies have been recognised in sheep, man, mink, captive deer and cattle. Recently a similar disease was reported in a domestic cat. This paper describes the clinical and pathological findings in five cats with similar signs, including further observations on the original case. All the cats had a progressive, neurological disease involving locomotor disturbances, abnormal behaviour and, in most cases, altered sensory responses. Histopathological examination of the central nervous system revealed changes pathognomonic of the scrapie-like encephalopathies, including widespread vacuolation of the grey matter neuropil, vacuolation of neuronal perikarya and an astrocytic reaction.

A 12-month abattoir survey was conducted between January 1999 and January 2000, to determine the prevalence of faecal carriage of verocytotoxin-producing Escherichia coli O157 (VTEC O157) in cattle and sheep slaughtered for human consumption in Great Britain. Samples of rectum containing faeces were collected from 3939 cattle and 4171 sheep at 118 abattoirs, in numbers proportional to the throughput of the premises. The annual prevalence of faecal carriage of VTEC O157 was 4.7 per cent (95 per cent confidence interval 4.1 to 5.4) for cattle and 1.7 per cent (1.3 to 2.1) for sheep, values which were statistically significantly different from each other (P < 0.001). The organisms were recovered from both cattle and sheep slaughtered throughout the year and at abattoirs in all regions of the country, but the highest prevalence was in the summer. The most frequency recovered VTEC O157 isolates were phage types 2, 8 and 21/28 in cattle and 4 and 32 in sheep, the five most frequently isolated phage types associated with illness in people in Great Britain during the same period.

During the decade to 1999, the incidence of human infections with the zoonotic pathogen verocytotoxin-producing Escherichia coli O157 (VTEC O157) increased in England and Wales. This paper describes the results of a survey of 75 farms to determine the prevalence of faecal excretion of VTEC O157 by cattle, its primary reservoir host, in England and Wales. Faecal samples were collected from 4663 cattle between June and December 1999. The prevalence of excretion by individual cattle was 4.2 per cent (95 per cent confidence interval [CI] 2.0 to 6.4) and 10.3 per cent (95 per cent CI 5.8 to 14.8) among animals in infected herds. The within-herd prevalence on positive farms ranged from 1.1 to 51.4 per cent. At least one positive animal was identified on 29 (38.7 per cent; 95 per cent CI 28.1 to 50.4) of the farms, including dairy, suckler and fattening herds. The prevalence of excretion was least in the calves under two months of age, peaked in the calves aged between two and six months and declined thereafter. The phage types identified most widely were 4, 34 and 2, which were each found on six of the 29 positive farms.