Prevalence and incidence of scrapie in The Netherlands: a questionnaire survey

Two independent nationwide surveys of randomly selected sheep farmers were conducted: in one a questionnaire was mailed to farmers and in the other the farmers were interviewed. The questionnaire was designed to obtain data on the occurrence of scrapie in the national sheep flock of the Netherlands. Farmers owning 30 or more ewes were selected from a database at the Ministry of Agriculture, Nature Management and Fisheries, resulting in 10,000 addresses. Two lists of names were compiled at random. In the postal survey 700 questionnaires were distributed, and 137 farmers were interviewed directly. The response rate in the postal survey was 37 per cent and in the interview survey 100 per cent. The results from the two surveys did not differ significantly. Six per cent of the farmers indicated that they had at some time observed signs of scrapie in their flock. For the total sheep population in the Netherlands, the prevalence of flocks with sheep showing signs of scrapie was between 3.8 per cent and 8.4 per cent (with 95 per cent certainty). In 1989 and 1990 the incidence rate within infected flocks was 1.27 cases/100 ewes/year, and the incidence rate for the total sample population was 0.1 case/100 ewes/year.