ON ES . 1998. 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 ). 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.

ON ES . 1998. A survey of the isolation rate and population size of thermophilic campylobacters in lambs at slaughter was carried out to determine the seasonal variation of thermophilic campylobacters in ovine hosts. Isolation rates determined by enrichment methods were always higher than those using direct plating onto selective agar and showed that Campylobacter could be isolated from 91·7% (n 360) of samples from the small intestine of the lambs. Enumerations (MPN), done monthly over a 2-year period, averaged 4·00 log 10 (n 1080, S.D. 0·16) campylobacters g −1 fresh weight (fw) intestinal contents with some samples giving values higher than 7 log MPN gfw −1 . These results show that the prevalence of thermophilic campylobacters in sheep intended for slaughter is much higher than previously reported. Statistical analyses showed that there was a significant seasonal periodicity in the Campylobacter populations in the small intestines of lambs at slaughter (P 0·004) but that there was no statistical relationship with environmental parameters such as minimum and maximum temperature, rainfall or hours of sunshine. In an analysis along the length of the intestinal tract of lambs, campylobacters were isolated from 80% of small intestine and 30% of rumen samples, but not from the true stomach, large intestine or caecal samples. A survey of sheep grazing on salt marsh, fell (upland) and farm pasture showed that the isolation rate of thermophilic campylobacters in fresh faeces was substantially lower (29·3% (n 420)) than that from the small intestine of lambs at slaughter. No significant difference (×0·05) was found between the isolation rate of campylobacters from faeces sampled in late spring/early summer and autumn, nor between the different types of grazing.

The small intestines and caeca of chickens were monitored for seasonal variation of thermophilic campylobacters over a 12-month period. There was a significant seasonal fluctuation in the carriage rate which correlated with the following environmental parameters: sunshine hours (P = 0.0003) and minimum (P = 0.007) and maximum temperatures (P = 0.003). The number of campylobacters in the small intestine and caeca also showed significant seasonal variation (P = 0.0008); however, the periodicity in the caeca was significantly different from that in the small intestine (P = 0.007). The numbers of Campylobacter in the caeca were significantly higher than those in the small intestine (P = 0.001). No significant correlation was found between the numbers of campylobacters in the caeca and small intestines and the environmental parameters monitored.

1997. The small intestines and caeca of chickens were monitored for seasonal variation of thermophilic campylobacters over a 12-month period. T h e r e was a significant seasonal fluctuation in the carriage rate which correlated with the following environmental parameters : sunshine hours (P= 0.0003) and minimum ( P = 0.007) and maximum temperatures (P= 0.003). The number of campylobacters in the small intestine and caeca also showed significant seasonal variation ( P = 0.0008) ; however, the periodicity in the caeca was significantly different from that in the small intestine (P=0.007). The numbers of Campylobacter in the caeca were significantly higher than those i n the small intestine ( P = 0.001). No significant correlation was found between the numbers of campylobacters in the caeca and small intestines and the environmental parameters monitored.

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