Microbial ecology of Campylobacter jejuni in a United Kingdom chicken supply chain: intermittent common source, vertical transmission, and amplification by flock propagation

Abstract

A study of Campylobacter jejuni on a broiler chicken farm between 1989 and 1994 gave an estimated isolation rate of 27% (3,304 of 12,233) from a 0.9% sample of 1.44 million broiler chickens from six to eight sheds over 32 consecutive rearing flocks comprising 251 broiler shed flocks. During the study, C. jejuni was found in 35.5% of the 251 shed flocks but only 9.2% (23 of 251) had Campylobacter isolates in successive flocks, with 9 of those 23 sheds having the same serotype between consecutive flocks, indicating a low level of transmission between flocks. Analysis of a systematic sample of 484 of 3,304 (14.6%) C. jejuni isolates showed that 85% were of 10 serotype complexes but 58% were of 3 serotype complexes, indicating a high degree of strain similarity throughout the entire study. The three commonest types were detected in 8 of 32 flocks during the 5-year study period, suggesting an intermittent common external Campylobacter source. This hypothesis was tested by a retrospective cohort analysis of C. jejuni rates and types by reference to hatchery supplier of the 1-day-old chicks. Isolation rates of C. jejuni and frequency distribution of types were determined in 6-week-old broiler chickens identified by the hatchery supplying the original chicks. The isolation rate of C. jejuni in broilers, supplied by hatchery A, was 17.6%, compared to 42.9% (P < 0.0001) for broilers reared from chicks supplied by hatchery B. In two instances, when both hatcheries were used to stock the same farm flock, Campylobacter isolates were found only in those sheds with chicks supplied by hatchery B. Thus, the frequency distribution of Campylobacter types for chickens supplied by the two hatcheries over the 5-year period showed marked dissimilarity. These findings suggest that the isolation rate and type of Campylobacter isolates in broiler chickens was associated with the hatchery supplying chicks. The lack of diversity of types and the intermittent high positivity of sheds is evidence for a common source of C. jejuni introduced by vertical transmission rather than contamination at the hatchery or during transportation.

Poultry as a source of Campylobacter and related organisms

“…The reason for the apparent lack of vertical transmission is thought to be due to: (a) poor survival of campylobacters on egg shells and inability to multiply inside the egg except in yolk (Clark and Bueschkins 1986;Shane et al 1986); (b) the low proportion of eggs either laid by infected hens, or after challenge with high numbers of campylobacters in faecal suspension, found to contain campylobacters (Doyle 1984;Shane et al 1986). However, Pearson et al (1996) and Cox et al (1999) did ®nd evidence, by typing strains, of low-level vertical transmission of Campylobacter by the breeding¯ocks to their progeny. If infection does take place by vertical transmission, the apparent delay of about 2 weeks before the birds become infected needs to be explained.…”

Scientific Opinion on Quantification of the risk posed by broiler meat to human campylobacteriosis in the EU

“…A UK study on serotypes in humans noted an increased rate of reporting drinking bird-pecked milk in individuals infected with strains of HS6, but this was the only positive association from many hypotheses tested and test statistics did not consider multiple comparisons (Sopwith et al, 2003). Use of serotyping to determine the origin of infections in a large study in chickens (3,304 isolates) was limited by lack of variation with three serotype complexes accounting for 58% of isolates and ten for 85% (Pearson et al, 1996).…”

Some potential sources for transmission of Campylobacter jejuni to broiler chickens

“…Poultry meat has been established as an important source of human infection with both Campylobacter jejuni and C. coli (Skirrow 1991;Pearson et al 1996). There is a general consensus that a significant reduction in human infections can be achieved by reducing Campylobacter infection in broiler flocks (Lindblom et al 1986;Evans 1992;van de Giessen et al 1998).…”