New hepatitis virus, test found.

New Hepatitis Virus, Test Found

Researchers at a commercial biotechnology firm reported this week the discovery of a virus responsible for up to 150,000 annual cases of transfusion-caused hepatitis in the United States, plus millions more worldwide. Linked to what is currently called blood-borne non-A, non-B hepatitis, the new virus has been partially cloned, providing reagents needed to develop a rapid screening test for the nation's blood supply and a possible future vaccine.

Identifying the virus at least partially solves the medical mystery of what causes the 95 percent of post-transfusion hepatitis cases not caused by the previously known hepatitis viruses, including those called A and B. The new, unnamed virus appears unrelated to any known virus, says Edward E. Penhoet, president of the Emeryville, Calif.-based Chiron Corp. Chiron scientists, collaborating with researchers at the Centers for Disease Control in Atlanta, first cloned parts of the virus last year, but only released their results this week at a scientific seminar at the University of California at San Francisco.

Antibodies to the virus have been found in "a very high proportion" of the hepatitis-infected blood tested in preliminary studies, Penhoet said at a press briefing in Washington, D.C. He says the percentage of positive results varies with the population tested, adding he expects the screening test now in development to detect at least 80 percent of donated blood units that are infected with non-A, non-B hepatitis viruses. "We can't be sure at this time that the agent we have cloned is responsible for all the non-A, non-B blood-borne hepatitis . . . but we think it represents the bulk [of cases]," Penhoet says.

Chiron scientists have sequenced about half the virus' genetic code, and produced several recombinant proteins using the viral genome as a template. One of those proteins apparently is found on the surface of the virus, and is being used in a prototype test to detect the virus. The company, which has applied for patents on the process, expects a blood-screening test to be worth $44 million in the United States and $107 million worldwide annually. In addition, use of the technology for diagnosing patients would bring the company another estimated $130 million. Penhoet says he expects clinical trials to begin this year. Currently, donated blood is screened for hepatitis B, as well as for a liver enzyme used to nonspecifically indicate the presence in donors of some sort of hepatitis infection.

Chronic hepatitis develops in 30 to 50 percent of those with blood-borne non-A, non-B hepatitis, and 20 percent of chronic carriers go on to develop cirrhosis. Evidence also indicates chronic carriers have a higher risk of eventually developing primary liver cancer. According to Penhoet, discovering the virus should make possible the development of a vaccine to prevent the disease. Earlier efforts to isolate a virus from infected tissues were stymied by the virus' refusal to grow in tissue culture and the lack of convenient animal models.