Varicella zoster virus

Ramsay Hunt syndrome (RHS), which has forced singer Justin Bieber to cancel his world tour, is a rare and painful complication of the virus that causes shingles and chickenpox.

RHS was discovered in 1907 by the neurologist of the same name. It is a rare neurological disorder that can inflame and then paralyze the facial nerve and cause a painful rash around the ear or mouth.

More than 2,000 cases of varicella have been registered since the beginning of the year, NOVA reports. This is what health authorities say.