Campylobacter and chickensJune 27, 2011
My last post looked at Campylobacter the bug and briefly described what can happen if we get infected by it. Now I’d like to talk about Campylobacter in chickens. After all, consumption of raw or undercooked poultry is the most common source of human infections.
A recent survey found that ~86% of UK broiler carcasses (broilers are those chickens that we grow for meat, rather than layers which obviously produce the eggs we eat) were contaminated with Campylobacter (either C. jejuni or C. coli) and the situation across Europe was found to be not much better with an average of 77% of carcasses being contaminated. (As with any disease, numbers of bacteria also matter when assessing whether bacterial carriage could cause disease. In this case many of the carcasses were carrying more than high enough numbers to be a risk to people.)
Now some of these carcasses may have become infected post slaughter but this still indicates that there is a large incidence of Campylobacter carriage in live chickens (something which has also been shown in epidemiological studies).
It’s known that broilers generally become infected by 2-3 weeks old and if they become colonised they go on to shed the bug in their faeces (so passing it on to others in the flock). It’s thought that the main way the bug gets into the house is through a breakdown in biosecurity: Campylobacter is also found in other farm animal species as well as wild animals and contaminated water sources.
In the past Campylobacter had always been considered a commensal of chickens (ie it doesn’t cause disease in the birds) but recent research is questioning this idea and this is something I will probably come back to in a later post. Commensal or not, it appears that broilers do not amount a sufficient immune response to clear the bacteria from their intestines which means they can carry it from infection right up until slaughter (at 6-8 weeks old normally).
Reducing the carriage of Campylobacter in chickens would (in theory anyway) dramatically reduce the number of human cases and so a lot of research is currently being carried in this area – watch out for future posts!
Citations and Further Reading
The ‘recent survey’ mentioned was this EU baseline survey
A good review to read (although unfortunately I don’t think it is open access) is: HUMPHREY, T., OBRIEN, S., & MADSEN, M. (2007). Campylobacters as zoonotic pathogens: A food production perspective International Journal of Food Microbiology, 117 (3), 237-257 DOI: 10.1016/j.ijfoodmicro.2007.01.006