Tuesday, November 21, 2006

So what is this Campylobacter thing?

Campylobacters are spiral-shaped bacteria (see picture above). They can infect both humans and animals, including birds. About 99% of the Campylobacter infections of humans are caused by just one species - Campylobacter jejuni. The micro-organisms appear to grow well in birds, which have a slightly higher body temperature than humans. Though chickens are often carriers, they show no symptoms of infection, so it's not possible to tell that the bird is infected without doing microbiological testing. C. jejuni does not grow below about 30C, so the presence of high numbers on chicken are unlikely to be the result of temperature abuse.

In humans the disease usually takes the form of abdominal pain and diarrhoea, which may contain blood, fever (typical of the body response to an infection), and vomitting may also occur. The symptoms usually last for about a week and usually no special medical intervention is required, but sometimes the patient requires hospitalization. There are some potential long-term consequences of infection - arthritis or Guillain-Barré Syndrome may follow infection. This is an auto-immune disease caused by the body's own defence system being triggered to attack the nerves. The incidence of Guillain-Barré Syndrome is estimated to be about 1 per 1000 cases.

Human infection is probably caused mainly by handling raw poultry, though the organisms may also be carried by farm animals and can be found in water supplies that have been contaminated by farm run-off. Though consumption of undercooked poultry has been suggested as a cause, in my opinion cross contamination in the kitchen (see "Should I eat the chicken?") is more likely.

The bacterium is easy to destroy by cooking. It cannot tolerate drying and can be killed by oxygen, so microbiologists have to take special precautions to handle and culture it - we grow Campylobacter in special containers where we can reduce the amount of oxygen present, replacing oxygen with carbon dioxide.

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