The exact cause of Guillain-Barré syndrome remains unclear. In most cases, a person with Guillain-Barré syndrome experienced some form of viral or bacterial infection some days or weeks prior to the onset of symptoms. The most commonly identified trigger is gastrointestinal infection with Campylobacter jejuni – one of the most common causes of food poisoning.
Some of the viral infections associated with the syndrome include respiratory and gastrointestinal infections, herpes zoster, glandular fever and viral hepatitis. Other triggers may be surgery or insect bites. Whatever the trigger may be, the immune cells of the body are prompted to attack and destroy the insulation of the nerve cells (myelin sheath). Sometimes, the nerve cell bodies (the axon) are targeted too.