Ironically, because past research studying the after-effects of exposure to things like atom bombs and radiation treatments for cancer suggests the most important environmental risk factor for meningiomas is ionising radiation.

ECONOMIST: Confirmation that dental X-rays can be bad for you

"As far as we know, it is still that example of the two people sitting by me as being at greatest risk, or someone who might touch the table where I have just put some droplets, or some environmental factor which is carrying these droplets to another person, " he added.

BBC: Scientists home in on mystery bug