- A mystery virus is contaminating blood
supplies throughout the world. No one knows whether this "TT"
virus is dangerous, but there are fears that it might cause liver disease.
- At the annual meeting of the American
Society for Microbiology, held in Chicago last week, researchers from California
reported finding the virus in apparently healthy blood donors. And a French
team announced that they had found TT virus both in blood donors and in
patients with liver disease undergoing transfusions.
- After the problems caused by HIV and
various hepatitis viruses, the discovery of any new virus in donated blood
is worrying. But while some TT virus carriers are suffering from liver
disease, it is not yet clear whether the TT virus is responsible. It's
also unclear whether the virus is spreading, or if it has been present
at about its current levels for many years. "No one knows the significance,"
admits Bernie Betlach of the Sacramento Medical Foundation Center for Blood
- The virus was named after the initials
of the Japanese patient in whose blood it was first found, two years ago.
Its discoverers, led by Hiroaki Okamoto of the Jichi Medical School in
Tochigi, isolated the virus from patients who had hepatitis-like symptoms
but no detectable hepatitis viruses in their blood.
- Last week, Betlach revealed that he and
his colleagues Paul Holland and Malcolm MacKenzie have isolated the virus
from 8 of 102 healthy blood donors in northern California. Blood from all
of the donors had tested negative for viruses including hepatitis B and
C and HIV.
- Marc Bogard of the General Hospital in
Meaux, France, also presented new data. Out of a total of 140 patients
receiving blood transfusions for liver disease from Meaux or at a collaborating
university hospital in Rouen, 33 carried the TT virus. Only 17 of the 140
tested positive for the virus that causes hepatitis C.
- From other studies on healthy donors,
Bogard estimates that between 4 and 6 per cent of the French population
is carrying the virus. About 13 per cent of people in Japan are thought
to be infected and in a paper published last July in The Lancet (vol 352,
p 191), the rate in Britain was estimated at 2 per cent.
- The challenge, Bogard says, is to find
out whether the virus poses any risk to health. "We are following
volunteers who have TT virus but are healthy and clear of hepatitis viruses
to see if they develop liver disease," he says.
- Bogard says that blood from the volunteers
will be monitored for the enzyme alanine aminotransferase, levels of which
are typically three times as high as normal in people with chronic liver
- Betlach, Bogard and other virologists
studying TT virus around the world are anxious not to cause panic, particularly
given recent experiences with a virus dubbed hepatitis G. This was linked
with chronic liver disease in 1995, but subsequently cleared.