Heart virus killed teenager

William Thode. Photo / Supplied

King's College student William Thode died from a viral infection of the heart.

The 15-year-old could not be roused by boarding school staff one morning in February.

Yesterday his mother, Kate Thode, said he had been suffering from myocarditis - a rare condition that causes inflammation of the heart.

"We don't know exactly how long he had it for ... probably only days," she said. "He was very fit and running around the track and swimming the night before.

"It's not something anyone would have been able to pick up ... It was just one of those freak things which causes quite a few young children and teenagers' deaths."

Auckland City Hospital cardiologist Dr Chris Ellis said myocarditis was a "sporadic" condition that struck without warning.

"Nobody can pick it up because you just feel unwell."

He said the virus could affect any part of the body, "but unfortunately with some people it can actually get involved with the heart [and] when that happens disaster can occur because there can be electrical disturbances of the heart and it can suddenly stop."