The epidemiology of Campylobacter jejuni in commercial broiler flocks in New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
Loading...
Date
2005
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
Rights
The Author
Abstract
New Zealand maintains the highest incidence rate of human campylobacteriosis of the industrialized countries (334.2 cases per 100,000 in 2002), it accounts for more than 56% of all disease notifications in the country. New Zealand is unique globally, with a 'notification-based surveillance system for notifiable diseases that is complemented by laboratory reporting. In other countries (Australia, US, UK), the notification system is entirely laboratory based. Thus, the high incidence of Campylobacteriosis in humans may be related to the methods of reporting rather than the reality of the disease situation. However, the reason for such high incidence has not yet been fully elucidated, and several studies conducted in New Zealand and overseas have implicated the consumption of poultry meat as the main cause of human infections. The reduction or elimination of Campylobacter jejuni in the food chain, particularly from poultry meat products, is a major strategy in efforts to control campylobacteriosis. One approach to this is to prevent C. jejuni colonization of broiler chickens, This approach has been used to control Salmonella contamination of poultry, but the measures put in place for control of Salmonella have not controlled C jejuni. It is generally unknown how frequently C. jejuni colonizes commercial broiler chickens in New Zealand, or what could be done to prevent these infections from occurring. The present study was undertaken in order to describe some of the basic epidemiology of C. jejuni in commercial broiler flocks in New Zealand. The thesis is intended to further describe the epidemiology of colonisation of commercial broiler chickens by C. jejuni in NZ, and present possible risk factors that could be controlled in future to decrease the number of positive flocks of birds that are processed. The thesis set out to elucidate first the extent of C. jejuni colonisation of birds, flocks and farms while the birds were on the farm, having had minimal risk of exposure to Campylobacter spp., by sampling 15 birds in 80 flocks belonging to two companies prior to the first partial depopulation, an event during which the flock are exposed to potentially contaminated fomites and biosecurity levels are dropped, doors opened and personnel movements are extensive. The resulting prevalence estimates are 25.6% of farms, and 12.5% of sheds, are likely to be used to rear broiler chickens colonised with C. jejuni. When a positive flock is discovered, 76.9% of the birds are likely to be colonised with C. jejuni. These figures are results across the whole study population of farms and sheds, as there were no significant differences between prevalence estimates between companies. Following this prevalence estimation, a longitudinal study was conducted involving 12 sheds, to determine whether the environment or the birds were colonised with C. jejuni first. Although 12 sheds were observed every other day from day 14 to the end of the rearing period, it was determined that the birds were positive either first, or at the same time as the environment. Having said that, the sensitivity of the testing method for the environment was dubious, as there were instances where a shed that had positive samples collected on one occasion appeared negative the next, before returning a positive result on the third consecutive sampling occasion. A cross-sectional study of 810 flocks was undertaken to determine the most relevant risk factors for colonisation of the broiler chickens with C. jejuni. Because of the vertically integrated structure of the poultry industry, these 810 flocks corresponded to data collected from 77 farmers about their farms and the 219 sheds on those farms. The caeca from ten birds from each flock processed were pooled and examined for the presence of C. jejuni. These results were used to create a case definition, such that the flocks could be analysed with the questionnaire data, and different risk factors were seen in each season. More flocks reared for Company One were colonised by C. jejuni than for Company Two. Protective factors included having hard (i.e. gravel, asphalt or concrete) pathways to the growout houses, being near to another broiler farm, using the reticulated town water supply for the birds drinking water, using tunnel or crossflow shaped growout houses, using a Chore-TimeTM feed delivery system within the growout house and chlorinating the water supply to the birds (only in winter). The odds of raising flocks colonised with C jejuni increased if rodents were seen on the farm, if the growout houses were constructed with a concrete nib wall, if gas heaters were used during brooding, if cattle were farmed on the property, or if workers were employed on the farm. Sanitising the annex at least as frequently as once per run decreased the odds during summer, and tended to have a similar effect in other seasons. Chlorinating the water supply appeared to have a protective effect in only one season, though the trend appeared towards protection in the other seasons. The risk factor was validated by sampling the drinking water that broilers chickens had access to for the FAC to sec whether the levels that were present in the drinking water could have an effect on C. jejuni 11 sheds that were known to chlorinate the water were sampled to determine whether they met the drinking water standards for humans in NZ, or met the requirements presented by one of the companies involved. Only three sheds met the human drinking water standards for FAC, and two of these (one from each company) met Company Two's requirements. This thesis is for both regulatory and industry stakeholders to assist with developing risk management approaches to diminishing the number of C. jejuni positive flocks. Where management practices are altered, it is hoped that the efficacy of such practices be measured by examining the changes in the rates of C jejuni colonization within the industry
Description
Irregular pagination: jumps from xix to 21
Keywords
Poultry diseases