Causes

Guillain-Barr syndrome is thought to be caused by a problem with the immune system, the body's natural defence against illness and infection.

Normally the immune system attacks any germs that get into the body. But in people withGuillain-Barr syndrome, something goes wrong and it mistakenly attacks the nerves.

This damages the nerves andstops signals from the braintravelling along themproperly, which can cause problems such asnumbness, weakness and pain in the limbs.

It's not clear exactly why this happens. The condition isn't passed from person to person and isn't inherited.

Possible triggers

Sometimes Guillain-Barr syndromeappears tohave a particular trigger. Some of the main triggers associated with it are outlined below.

Infections

In about two in every three cases,Guillain-Barr syndromeoccurs a few days or weeks after an infection.

Infections that have beenknown to trigger the condition include:

• food poisoning especially if caused by Campylobacter bacteria
• Bird flu
• cytomegalovirus a common virus that doesn't usually cause any symptoms
• glandular fever
• HIV
• some travel infections, including dengue and the Zika virus

Vaccinations

In the past, vaccinations (particularly the flu vaccine used in the US duringaswine flu outbreak in 1976)were linked to an increased risk of Guillain-Barr syndrome.

But research has since foundthe chances of developingthe condition after having a vaccination areextremely small.

For example,a study into the vaccine used during the 2009 swine flu outbreak found that for every million people who had the vaccination, there werelessthan two extra cases of Guillain-Barr syndrome.

The benefits of vaccination are likely to outweigh any potentialrisk, as infections such as fluare more common triggers ofthe condition.

Other triggers

Other possible triggers forGuillain-Barr syndrome include:

• surgery
• an injury
• medical procedures such as a bone marrow transplant