Common viral triggers include glandular fever or Epstein-Barr virus (EBV). Other herpes viruses such as herpes simplex, VZV (causes chickenpox/shingles), HHV-6 and CMV, may sometimes trigger M.E., as can viral meningitis or labyrinthitis, commonly caused by enteroviruses, gastroenteritis, Hepatitis A, B and C infection, and in Australia, Ross River virus.
Non-viral triggers include toxoplasma, brucella, salmonella, tuberculosis, Q fever, and Lyme disease.
However, there is no clear evidence that M.E. is a form of persistent, chronic infection - it may be a consequence of infection.
It is not clear why some people get M.E. while others recover normally. People who get M.E. may be vulnerable genetically, or their recovery after an infection could be affected by, for example, trying to return to work too soon, doing vigorous exercise, or experiencing major stresses.
We know much less about other triggers, because they are less common. Some people may in fact have had an infection, but didn’t notice it at the time.
Less common triggers
In a very small number of people, the trigger may have been an immunisation, given perhaps when they were already unwell, or a physical trauma, such as a road accident, operation, radiotherapy or chemotherapy, or whilst rare, it is suspected that a very few cases may be triggered by certain toxic substances.
One big outstanding question is whether emotional stressors can be a trigger. Studies are not clear, some suggesting a link and others not. It is unlikely that stressful life events, such as bereavement, can trigger M.E. on their own.
Often it isn’t possible to find out exactly what caused your illness - but you can still improve your symptoms, despite not knowing the exact trigger.