A patient taking Novartis' multiple sclerosis pill Gilenya developed a rare and potentially fatal viral disease, the Swiss drugmaker said on Tuesday, an unexpected setback as it faces growing competition from new oral treatments.

Gilenya is one of Novartis' big new drug hopes, growing 66 percent in the second quarter to $468 million. But the drug faces competition from new medicines such as Biogen Idec's Tecfidera.
Novartis said it had been informed of a case of progressive multifocal leukoencephalopathy (PML) in a patient who had been taking Gilenya for MS for seven months.