Descriptive analysis of the results of an anonymous postal survey of the occurrence of scrapie in Great Britain in 2002.

An anonymous postal survey was conducted in 2002 to estimate the proportion of farms in Great Britain affected with scrapie and to gather information on the likely risk factors for the occurrence of the disease; the response rate was 53 per cent. The survey showed that 1 per cent of the respondents thought they had had scrapie in their flock in the previous 12 months, and that 12 per cent thought they had had scrapie in the past. The results of the survey were consistent with the results of a similar survey carried out in 1998, and with notification patterns, but in 1998 approximately 3 per cent of farmers reported having had scrapie in the previous 12 months. It is not clear whether the apparent decrease in the prevalence of scrapie is real or whether it may be due to factors such as sampling biases, or to the increasing knowledge of the signs of scrapie shown by the respondents in 2002.

Analysis of clinical signs associated with bovine spongiform encephalopathy in casualty slaughter cattle.

Clinical signs associated with bovine spongiform encephalopathy (BSE) were studied in 1008 casualty slaughter cattle over 30 months of age to compare the results with the BSE status as determined by postmortem tests. The clinical BSE status was assessed using seven different criteria based on various publications. Only one (0.10%) out of 997 casualty slaughter cattle with a matching postmortem test result was positive for BSE. The BSE case was identified by only two case definitions tailored specifically to recumbent cases. The variety and often equivocal definition of clinical signs associated with BSE is reflected by the difference in the criteria that usually identified different animals as BSE suspects. The BSE status may be more difficult to assess in recumbent animals that do not allow a full clinical examination, and BSE may not be suspected if another disease is present that may mask signs of BSE.

Results of a postal survey of scrapie in the Shetland Islands in 2003.

In February 2003, a postal survey of 1279 sheep farmers in the Shetland Islands yielded 586 responses (46 per cent response rate). The principal aim of the survey was to gather information on the history and control of scrapie. Overall, 28.5 per cent of the respondents thought they had had a case of scrapie in their flock at some time. There was a slow increase in the proportion of affected flocks during the 1970s, followed by a more rapid increase during the 1980s and early 1990s, and a decline from the mid-1990s onwards. The peak proportion of affected flocks was approximately 6 per cent in 1994. Of the farmers who had ever had scrapie in their flock, 97.1 per cent had attempted to control the disease. The most common method of control was breeding from non-susceptible tups, used by 90.6 per cent of the affected flocks and 75.1 per cent of the flocks that had never been affected. A comparison of the characteristics of the affected and unaffected flocks indicated that an increased risk of scrapie was associated with the larger flocks, the open flocks and the flocks that bought in lambs. The basic reproduction ratio for the spread of scrapie between flocks was estimated to be 1.47, and the mean duration of an outbreak within a flock was estimated to be approximately two years.

Frequencies of PrP genotypes in 38 breeds of sheep sampled in the National Scrapie Plan for Great Britain.

Between October 2001 and January 2003 the prion protein (PrP) genotypes of over 250,000 sheep were determined through the operation of the National Scrapie Plan (NSP); the results for 38 breeds were analysed to provide an estimate of the underlying PrP genotype distribution of the British sheep population. Although there was marked variability among the genotype profiles of the different breeds, several trends emerged. A comparison of the allele frequencies demonstrated that the breeds could be grouped into three categories: breeds dominated by ARR and ARQ in which the frequency of ARR exceeded the frequency of ARQ; breeds dominated by ARR and ARQ in which the frequency of ARQ exceeded the frequency of ARR; and breeds with significant levels of either AHQ, ARH or VRQ. Hill breeds were more likely to have a lower proportion of animals at low risk of scrapie (NSP type 1) and a higher proportion of animals at an intermediate risk of scrapie (NSP type 3) than other breeds. Most breeds had a small proportion of animals at high risk of scrapie (NSP type 5). The frequency of ARR/VRQ (NSP type 4) was variable.