Medical sleuths have lifted an indictment against a suspected hepatitis virus. Two studies in tomorrow's New England Journal of Medicine all but remove the blame from the so-called hepatitis G virus (HGV), which is found in 1% to 2% of blood donors. That's good news for blood banks, which have no way to screen directly for HGV--but it also forces investigators to redouble their efforts to ferret out the real culprit behind certain mysterious cases of hepatitis.
Any of a host of proven attackers--viruses transmitted by infected blood or contaminated food--can cause hepatitis, an inflammation of the liver. The most virulent pathogens, the B and C viruses, can also lead to liver cancer. But in about 5% of cases of chronic liver disease, doctors can't find any trace of a known pathogen. Last year, two research teams found a new virus--HGV--in the blood of some patients with this disease, called hepatitis of unknown origin. Put in a genetic criminal lineup, the RNA of the virus bears a marked resemblance to hepatitis C.
The new studies, however, seem to exonerate HGV. Harvey Alter, a blood researcher at the National Institutes of Health, and colleagues at the NIH and at Genelabs Technologies in Redwood City, California, used the polymerase chain reaction to probe for minute quantities of HGV RNA in 357 patients who had received transfusions during open heart surgery, 79 of whom went on to develop hepatitis. Only three of the 79--less than 4%--were infected with HGV. Most had the C virus, and 10 patients had no known pathogen. Moreover, HGV infection rates were the same for transfusion patients with or without hepatitis. A similar study in the same issue, by the Centers for Disease Control and Prevention in Atlanta, suggests that HGV is unlikely to play a role in "community acquired" hepatitis, a catchall category for hepatitis contracted through food, sex, or dirty needles. Says Alter, "HGV could be an innocent bystander."
But experts are unwilling to close the books on HGV. "We must keep HGV under suspicion," asserts Makoto Mayumi of the Jichi Medical School in Tochigi-Ken, Japan. "We need more evidence before we can reach a final verdict about HGV." The NIH researchers agree. "It's hard to prove something doesn't cause disease," says Alter, who plans to keep interrogating HGV and other suspects behind those unexplained cases of hepatitis.