A longitudinal study of Campylobacter spp. on a New Zealand dairy farm : a dissertation presented in partial fulfilment of the requirements for the degree of Master of Veterinary Studies (Epidemiology) at Massey University

Although Campylobacter is a common cause of gastroenteritis in humans in New Zealand, the source of infection usually remains unknown. However, the high frequency of human infection may be due to the relatively low infectious dose. Campylobacter jejuni and some other Campylobacter species are commonly found as commensals in livestock in cluding cattle which may be reservoirs for a number of Campylobacter species. The objective of this study was to estimate the prevalence of Campylobacter carriage in healthy dairy cows at the study farm. The combined epidemiological and microbiological investigation was useful in conducting a longitudinal study of Massey University No. 4 Dairy Farm in this project. The project surveyed cows of different ages in the herd at different times over the study period. In order to determind whether strains of C. jejuni isolated from the cows were identical, Pulse-Field Gel Electrophoresis was applied to examine the similarities among C. jejuni isolates. Based on the results of an initial pilot study, selecting a suitable sample size of dairy cows for planned sampling events saved time and cost in estimating the Campylobacter prevalence. In this study, on a basis of the results of pilot study, a sample size of about 60 animals was selected in order to estimate 90% confidence level within 10% accuracy. Finally, the results of prevalences of Campylobacter at different samplings were applied to calculate 95% confidence intervals for prewvalences in different populations