Two years ago Fleur Senior, then 14, was considered by her teachers to be on course to read maths at Oxford University. A bright child, she was also the fun-loving lynchpin of a gaggle of girls at school. She loved playing hockey and tennis, as well as practising on her trombone and the piano.

The only cloud on Fleur’s horizon was a recurrent problem with glandular fever. Four bouts over two years had drained some of her bountiful energy. Blood tests by a paediatrician had found evidence of a series of infections with the Epstein-Barr (EB) virus, a member of the herpes family that causes glandular fever.

But it was another viral infection that was to have a devastating effect – leading to serious neuro-psychiatric problems such as hallucinations and self-harming, says her mother Helen, 56, a finance director and married mother of two.

Fleur, now 16, hasn’t been able to return to school full-time since.