Determining the Role of Maternal Antibodies in the Lag Phase of Campylobacter Jejuni Infection in Chickens

Project final report summary : Despite the number of cases falling in recent years, Campylobacter jejuni remains the leading cause of bacterial enteritis in the UK, with over 40,000 cases reported in England and Wales in 2004 (CDSC report). Further, a large scale study for the Food Standards Agency estimated that in the community there are up to eight times more unreported cases than reported. Moreover, the large numbers of cases each year results in C. jejuni inflicting a heavy, social and economic burden upon the country. Although the routes and sources of transmission are not fully understood, the handling and/or consumption of contaminated poultry meat is believed to be a risk factor. Indeed, most broiler flocks within the UK appear to be highly colonised . Despite considerable efforts by the industry, approaches to introduce practical enhanced bio-security strategies have failed to achieve predictably negative flocks at slaughter. Given the high level of flock colonisation and the intensity of poultry processing, a multi-pronged and interactive approach to intervention at the farm level is likely to be the most effective approach. <P>
A striking feature of the epidemiology of C. jejuni/coli in broiler flocks is the apparent absence of colonising organisms within the first 2-3 weeks of the birds’ lives . After this period, the whole flock is rapidly colonised. This delay in the onset of colonisation, known as the lag phase, represents a window of opportunity to apply controlling strategies. Moreover, understanding the underlying mechanisms of the lag phase may also provide answers to successful control. Prolongation of the lag phase by 4-5 weeks could result in birds being significantly less colonised at the point of slaughter. Thus, understanding the lag phase should help in Defra’s aims to 'develop practical measures to reduce Campylobacter infection in poultry'.<P> The aim of this project was to determine the role of maternal immunity in the lag phase. Specifically, the main objectives were:
<OL> <LI> To determine the role of the farm environment in the lag phase.
<LI> To develop an experimental model of the lag phase.
<LI> To measure specific antibody levels in commercial breeders and their eggs. </ol>

In order to study the lag phase in detail, three breeding flocks were established at VLA. Two were commercial broiler breeders and the other white leghorns (WLH), the breed used for specific pathogen free birds used in experimental studies. The WLH and one of the broiler flocks were infected at 9–weeks-old with C. jejuni strain M1. The infection appeared to be cleared within 6 weeks, followed by a decline in antibody levels, so birds were re-challenged prior to lay in order to maximise any effects of maternal immunity. Fertile eggs from the three flocks were hatched and the chicks challenged between 1- and 22-days-old with a range of doses and strains of C. jejuni. In all, four challenge experiments were done. The results consistently showed that chicks derived from infected parents were less easily colonised at 1- and 2-weeks old than chicks from uninfected parents. This protection was seen both against the homologous strain (M1) and heterologous strains (81116 and 11168-O). However, protection in the first few days of life was less clear-cut. Birds from infected parents were more susceptible to colonisation at 1-day-old than at 8-days old. This was investigated in more detail in the final experiment by challenging at 1-, 2-, 3- and 6-days-old. Birds from uninfected and infected parents were all maximally colonised at 1-day-old by a comparatively low dose (560cfu). However, birds from infected stock became increasingly resistant to colonisation over the course of the experiment. The precise reasons for this observation are unclear at present, but are probably associated with the stress of hatching. Antibody levels in the chicks used in these challenge experiments were monitored over the first 3 weeks of life. As expected there were high levels of anti-C. jejuni antibodies in birds from infected parents that declined steadily over three weeks. Apart from the susceptibility seen in the 1- and 2-days-old birds, antibody levels in the groups of birds from infected parents correlated to susceptibility to colonisation.
<P> This pattern of colonisation over the first few weeks of life was also observed in chicks brought in from a commercial broiler house. The campylobacter status of their parents was unknown, but there were high levels of anti-C. jejuni antibodies in the chicks, suggesting the parents were, or had been, infected. The commercial broiler flock from which these chicks came was also monitored for infection. No C. jejuni was detected in birds up to 4-weeks-old (when the study ended).
If maternal immunity in commercial birds is an important determining factor in the lag phase, then the levels of specific antibodies present in breeding hens and their eggs may be indicators of the susceptibility of chicks to colonisation. In view of this, the antibody levels in the eggs from a single flock were monitored over the laying life of the flock. Antibody levels in eggs taken every fortnight from the start of lay were measured by ELISAs using pooled antigens from the five commonest serotypes of retail poultry-associated C. jejuni. There was considerable fluctuation in levels over the course of the study, but levels were always considerably higher than in eggs taken from C. jejuni-naïve birds. The fluctuations may be associated with exposure to a number of strains, immune clearance and re-exposure to the same or new strains. These fluctuating levels may lead to some variability in susceptibility to colonisation in different batches of chicks. However, results from the experimental challenge studies suggest the maternal-derived immunity is unlikely to last any longer than 3 weeks, leaving sufficient time for commercial flocks to become infected before slaughter.
<P> Taken together, these results suggest maternal immunity plays an important role in the lag phase of infection seen in commercial broiler houses. However, the apparent susceptibility of ‘immune’ newly-hatched chicks suggests birds are not exposed to campylobacters at this stage of life. Nevertheless, at later ages birds evidently are exposed. This work confirms immunity can be important in determining colonisation, offering further hope that vaccination may be feasible. Whether hyperimmunisation of breeding birds can extend the lag phase remains to be seen. This does merit further investigation as any extension of the lag phase provides a greater window of opportunity for other intervention strategies applied to chicks to take effect.

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