One of our most common food-borne "tummy bugs" might also be responsible for cases of a paralytic disease which occurs more frequently than polio in western countries.
The villain of the piece is campylobacter jejuni, the commonest cause of gastro-enteritis worldwide. It is a regular visitor to our homes via untreated milk or water and in undercooked poultry.
"There are increasing concerns at the level of illness caused by C jejuni infection, which now exceeds the combined total of enteritis cases caused by salmonella, E coli and shigella," says Dr Anthony Moran, a senior lecturer in the department of microbiology at NUI Galway.
The symptoms of C jejuni are the usual diarrhoea, nausea and cramps, but the bug also has a much more serious side. It has been implicated in a rare neurological complication known as Guillain-Barre Syndrome (BGS), a disorder which can lead to severe paralysis and in some cases death.
The syndrome affects up to two people per 100,000 of population each year, representing about 40 to 50 new GBS cases here each year. It is slightly more common in men than women and incidence increases with age, says Dr Moran.
Symptoms begin with tingling in the toes and tips of the fingers, followed by weakness, numbness and later paralysis in the limbs. Most people begin to recover within three to 12 months, but 20 per cent of cases are left with a permanent disability, including total paralysis, and about 5 per cent of patients do not survive.
"GBS has replaced polio as the leading cause of infectious paralytic disease," says Dr Moran.
Only certain strains of the bug can actually cause GBS, however, so it is important for clinicians treating patients to establish the cause of any enteritic disease very quickly.
Dr Moran and a Galway research team, including Dr Martina Prendergast, have developed a rapid test which can detect the strains of C jejuni which can cause GBS. "Hundreds of strains can be screened quickly and cheaply, and the test could be routinely used in hospital laboratories to detect potential disease-causing strains," says Dr Moran.
The test was developed under a three-year project funded by the Health Research Board. It also involves co-operation with other research labs in Ireland, the US and South Africa.
The link between GBS and C jejuni emerged during the 1980s. Up to 75 per cent of GBS cases involved previous exposure to the bacterium, says Dr Moran. It was discovered that certain chemicals on the surface of the bacterium, known as glycolipids, were identical to structures found on the surface of nerve tissues.
Infection with C jejuni sets the scene for serious nerve fibre damage when the body's immune system becomes confused when identifying "self" and "enemy". The immune system raises antibodies against Cjejuni glycolipids, but surface structures on the nerve cells look the same.
The antibodies clear the bacterium but then attach to the nerve fibres. Once connected the antibodies flag down phagocytes, white blood cells which begin to destroy the mylin sheath which protects the nerve fibre. If this autoimmune response is not checked permanent damage can result.
"Even though [C jejuni] is a common infection at least some strains can cause problems," says Dr Moran. "The test allows us to say this particular strain has the potential to lead to GBS."
Early diagnosis allows an early intervention before much damage has been done, he says. The antibodies which do the damage can be filtered out of the blood, thus halting the damage.
The rate of C jejuni infection here is rising but it is not clear why, says Dr Moran. There were 2,085 cases confirmed by lab tests during 1999, but the true case load is probably much higher. "We believe it has a much higher incidence in Ireland than reported."
Diagnosis is better but because the infection is usually slight many patients don't report their illness to GPs and few GPs bother to send off samples to confirm C jejuni infection. The rapid test for GBS-related strains may become an important diagnostic tool in limiting the impact of the syndrome.