Campylobacter jejuni is one of the world's major food poisoning bacteria. British scientists have recently determined its entire genetic make up, which should lead to an understanding of the mechanism of Campylobacter virulence as well as strategies to control it. Campylobacter jejuni has been taken seriously as a food pathogen only since the 1970's, but it is probably responsible for maybe twice as many cases of reported enteritis than the better known Salmonella. Originally thought to be a harmless organism living within some animals, one of its mysteries is how it lives in the gut of birds without causing disease but becomes an invasive pathogen in humans. It has a very low infective dose and over the last 20 years the incidence of Campylobacter food poisoning has soared in developed countries. Healthy humans do not carry the organism nor is it passed from infected humans to other people. The main symptom of infection from contaminated food or water is diarrhoea, but others such as fever, nausea, headache and abdominal pains can also occur. Illness typically starts 2-5 days after ingestion of the bacteria and the effects can be very debilitating, lasting for up to 10 days.