A simple test could dramatically cut the number of cases of food poisoning.

US government researchers have developed the test for the bacterium Campylobacter.

Campylobacter is responsible for four times as many food poisoning cases as Salmonella.

The most common symptoms of campylobacteriosis are diarrhoea, abdominal pain, tiredness, fever, nausea, and vomiting.

The symptoms most often show up two to five days after the germs have been swallowed.

The bacterium is also thought to cause between 20 and 40% of cases of Guillain-Barr� syndrome, a severe neural disorder that can make people so weak they may need help breathing.

But until now there has been no quick or reliable test for the bacteria in livestock or food.

In another breakthrough, scientists have developed a scanner that can reveal whether cattle carcasses are contaminated with faeces that could cause disease.

Iren Wesley, of the National Animal Disease Center (NADC) in Ames, Iowa, said: "Campylobacter has not had the attention of other food-poisoning bacteria.

"It is hard to grow in the lab, and while it makes more people sick than, say, Salmonella, it kills less frequently."

Until now, diagnosing Campylobacter infections or identifying the bacterium in food involved weeks of culturing.

The methods used to distinguish the most dangerous species were also unreliable.

Cows and pigs infected

Pigs are also infected with the bacterium

But New Scientist magazine reports that Wesley and her colleagues have solved both problems with a test that uses the polymerase chain reaction to amplify Campylobacter's DNA.

The test takes only eight hours to complete and can reliably identify the worst culprit, Campylobacter jejuni, as well as several other species.

The first trials of the test have revealed that 39% of healthy dairy cattle in the US carry C. jejuni in their faeces, which can contaminate milk and carcasses at slaughter.

It is also present in the faeces of up to 70% of healthy adult pigs and 90% of piglets.

The researchers say they are comparing the two main methods for intensively raising pigs - keeping a barn occupied continuously or periodically emptying and cleaning it - to see which leads to most infection with Campylobacter.

They are also trying to develop an even simpler test for the bug that could be used by farmers to detect and treat early infection.

The NADC has also developed a scanner to prevent faecal contamination of meat.

The scanner emits light at a wavelength that makes several bacteria found in cattle faeces fluoresce.

Contaminated areas show up as green spots on the carcass, which can then be trimmed or cleaned.