The epidemiology of clinical cases of campylobacter in temperate climates shows a striking seasonality. In the search for a seasonal environmental reservoir changes in the carriage rate and population size of campylobacters in bovine hosts with time have been measured. Most probable number (MPN) methodology was used to enumerate thermophilic campylobacters in samples taken from the small intestines of beef cattle at slaughter and the fresh faeces of four dairy herds and new-born calves. Statistical analyses revealed significant evidence for seasonal periodicity in the data from dairy herds (P = 0·044). Not only was there a departure from constancy within a 12-month interval but these data revealed a true seasonality, that is, the same periodicity in numbers from one year to the next. Each herd had two peaks per year, in approximately spring and autumn. Peaks coincided in herds on neighbouring farms but those on farms in the north preceded those on farms in the south by 2 and 1 months, respectively (P = 0·0057). Intestinal carriage by beef cattle at slaughter was 89·4% (n = 360) with an average MPN campylobacters per gram fresh weight (MPN gfw−1) of 6·1 × 102. Average MPN gfw−1 in faeces from the dairy herds and calves were 69·9 (S.D. 3) and 3·3 × 104 (S.D. 1·7 × 102). There was no evidence of seasonal periodicity in the size of the campylobacter population in beef cattle at slaughter. Calves were campylobacter free at birth but became colonized within a few days.
Present address: Department of Life Sciences, University of East London, Romford Road, London E15 4LZ, UK.