Researchers have known for years that some adenoviruses - which cause flu-like symptoms - can weaken the heart muscle, leading to sudden death or eventual heart failure in children.

But until now it has not been shown that the same risk exists for adults.

The research could lead to new ways of treating and preventing left ventricular dysfunction (LVD), a condition that can cause sudden death.

Enlarged heart

The viruses affect the upper respiratory tract. In rare circumstances, LVD occurs a few weeks after the flu-like symptoms.

The usual symptoms are fatigue and shortness of breath. An X-ray may reveal heart enlargement.

This can cause damage to the heart muscle.

In some patients, drugs can be used to strengthen the heart's pumping ability, but for a few a heart transplant may be needed.

If the condition goes undetected, it can cause sudden death.

LVD can be caused by a range of factors, including underlying coronory heart disease, a genetic defect and even tissue damage caused from using cocaine.

In the USA, there are between two and eight new cases of LVD per 100,000 people every year.

Some 40 out of every 100,000 people are estimated to suffer from the condition which costs around $12bn a year to treat.

Enteroviruses

Dr Jeffrey Towbin, of Baylor College of Medicine in Houston, led the research into adenoviruses.

He identified that the viruses cause LVD in children in the early 1990s.

Until then, it was thought that the only viral link to LVD was through enteroviruses - which are thought to be behind a variety of illnesses, including the common cold and meningitis.

LVD affects 40 out of 100,000 Americans a year

Dr Towbin, a specialist in children's heart disease, says adenoviruses are a more common cause of LVD in children than enteroviruses.

"Adenoviral infections are at least 10 to 15% more common in the heart muscle of children with LVD than than enteroviral infections.

"Typically a child gets a cold, it lingers four or five days and goes away. Three weeks later, the child starts feeling bad, and that's when the heart enlarges and pumps poorly."

He added: "LVD is not a common disease, but it has a major impact. When you see a high school student drop dead playing sports, LVD is one of the common causes."

Dr Towbin and his team studied heart tissue from 94 adults aged 17 to 76. All had LVD, but the cause was unknown.

Using a genetic test, the researchers found evidence that 12 of the adults had suffered from an adenovirus - around the same number as those who had suffered from an enterovirus.

"These findings are similar to data from paediatric patients," they said.

The researchers think their findings could lead to new ways of treating or preventing LVD.

A vaccine exists against some adenoviruses, but Dr Towbin says it is likely not to be effective against the adenoviruses that cause LVD.