The potentially fatal hepatitis C virus could be passed on by kissing or sharing toothbrushes, a study suggests.

Researchers in the United States say they have found traces of the virus in the saliva of people with hepatitis C.

They believe the saliva may be infectious and that people with the virus could pass it on to others.

Speaking at the Interscience Conference on Antimicrobial Agents in Chicago, they said people with gum disease may be most at risk.

Millions affected

Hepatitis C is a blood-borne virus. It is spread when blood from an infected person gets into the bloodstream of another.

The World Health Organisation estimates there are 170 million carriers of hepatitis C worldwide. Infection rates in the UK are relatively low, with an estimated 0.4% of people in England infected.

The virus affects different people in different ways. Many experience no symptoms at all while others experience extreme tiredness and can feel very unwell.

Reported symptoms include fatigue, weight loss, nausea, flu like symptoms, problems concentrating, abdominal pain and jaundice.

As many as one in five are able to clear their infections naturally within six months. For the remainder, hepatitis C is a chronic infection that can span several decades and can be life-long. It can lead to serious liver disease and even death.

Researchers at the University of Washington in Seattle tested the saliva of 12 people who were infected with hepatitis C every day for 21 consecutive days.

Of the 248 samples taken, 52 or one in five tested positive for the virus.

Traces were found in the saliva of seven of the volunteers. However, none of these tested positive everyday. On average, they had traces of hepatitis C on seven out of the 21 days.

Those most likely to have traces of the virus in their saliva had relatively high levels of the virus in their body.

They were also more likely to detect the virus in saliva if the volunteer had gum disease.

They said this may occur when the gums bleed after brushing, leaving tiny drops of blood in the saliva.

Infectious saliva

The researchers told the conference that the findings could have implications for people who are infected with the virus.

'This study suggests that the saliva of individuals infected with hepatitis C may be infectious,' they said.

'Microscopic amounts of blood in the saliva due to gum disease may be responsible.

'People with HCV (hepatitis C virus) are cautioned not to share toothbrushes with other people in the household.'

The findings suggest the virus could also be spread from kissing.

Basil Williams, chief executive of the UK's National Hepatitis C Resource Centre, said more research is needed to determine if it is possible to catch the virus from kissing.

'The jury is still out in the medical profession about the level of risk posed by kissing,' he told BBC News Online.

'In relation to the transmission of hepatitis C, it is technically possible to catch hepatitis C from kissing but the risk appears to be very small.'