New Blood Test Able to Identify Type of Hepatitis
Researchers at a Northern California biotechnology firm have developed an experimental blood test for the most common form of blood-borne hepatitis, according to two articles in today’s issue of the journal Science.
The advance could markedly improve the safety of the world’s blood supply and speed the development of a vaccine against “non-A, non-B hepatitis,” a liver ailment than can be debilitating and in some instances contribute to death.
The researchers, from Chiron Corp. in Emeryville, said that the new test may detect up to 80% of the transfusion-acquired non-A, non-B cases in the United States. These cases appear to be caused by the “hepatitis C” virus, which the Chiron scientists recently identified. The other cases are likely to be caused by yet-to-be-discovered viruses.
‘Phenomenal Development’
“This is a phenomenal development,” said Dr. Jay E. Menitove, medical director of the Blood Center of Southeastern Wisconsin in Milwaukee. “AIDS is not the leading problem with the blood supply. We are on the verge of making a big dent in the most frequent transfusion-transmitted infection,” non-A, non-B hepatitis.
The new lab test is being extensively evaluated in the United States, Italy and Japan. If it proves accurate, “we hope that it will be on the market by early 1990,” Larry Kurtz, a Chiron spokesman said.
An estimated 150,000 non-A, non-B hepatitis infections occur in the United States each year, according to Dr. Miriam J. Alter, chief of national hepatitis surveillance for the U.S. Centers for Disease Control.
Between 5% and 10% of the cases are estimated to occur in blood transfusion recipients and 40% in intravenous drug users, Alter said. Some of the additional non-A, non-B cases appear to be related to sexual intercourse or other intimate contact.
The risk of contracting non-A, non-B hepatitis may be 3% to 6% for transfusion recipients, who typically receive several units of blood. The risk of contracting the AIDS virus is minimal by comparison--less than one in 40,000 for each unit of blood transfused.
The first scientific publication of the Chiron research also appears to confirm the company’s announcement last May that it had discovered an elusive non-A, non-B hepatitis virus. The infection has been so-named to distinguish it from other forms of hepatitis with known causes.
‘Important Disease’
“At last we have a handle on this important disease in man,” Michael Houghton, the Chiron scientist who led the research team, said in an interview. The team also included Daniel W. Bradley of the CDC, and for the development of the blood test, researchers from the CDC, the National Institutes of Health and a number of medical schools, including UCLA and USC.
Over the last year, Chiron scientists have extended their earlier research into the mysterious virus that has been thought since the early 1970s to be responsible for most non-A, non-B hepatitis in the United States.
The researchers have cloned the viral genetic material, which was initially identified in a patient with chronic hepatitis, according to the reports. They have also determined about 90% of the chemical structure of the viral genes and obtained laboratory evidence of the agent in chimpanzees inoculated with infectious particles.
Unable to Grow Virus
But Houghton acknowledged that the researchers have yet to grow the virus in a pure form in the laboratory, isolate virus particles, or see the virus under the electron microscope.
“To our knowledge, this is the first time someone has cloned an infectious agent and developed a test for infectious blood without actually having cultured the virus or identified the infectious particle itself,” Houghton said. “That really is a testament to the power of genetic engineering.”
The symptoms of acute viral hepatitis include severe fatigue, nausea and jaundice. Only about a quarter of non-A, non-B infections cause such symptoms, according to the CDC’s Alter. But the infections may be quite significant nevertheless.
Infected individuals may transmit the disease to others, and 50% or more may develop chronic liver inflammation, Alter said. Some eventually develop the life-threatening scarring of the liver called cirrhosis.
Efforts to safeguard the blood supply against non-A, non-B hepatitis have been hampered by the lack of an accurate laboratory test. Universal blood screening with indirect blood tests began in late 1986, but is estimated to detect only 40% to 50% of infected units.
The new blood test detects antibodies to hepatitis C, which are immune system proteins produced by the body in response to the viral infection. It does not directly detect viral particles.
Important Limitations
But the test appears to have important limitations, according to Bradley and Alter of the CDC. For example, a positive test does not indicate how recently an exposure occurred or whether an individual remains infectious to others.
The test appears to frequently remain negative for up to six months after infection. Thus it may fail to detect tainted blood donations from individuals that have recently been exposed to the virus.
In addition, until improved hepatitis C blood tests are developed, it may have little value for physicians in diagnosing patients with acute hepatitis or in counseling patients with positive tests about their infectivity to others.
In preliminary trials, hepatitis C antibodies were detected in about 80% of 79 chronic non-A, non-B blood transfusion hepatitis cases from the United States, Italy and Japan, according to the Science articles.
Particularly significant were highly accurate results on a panel of test blood samples maintained by Dr. Harvey J. Alter at the NIH in Bethesda, Md. Previous non-A, non-B blood tests have dismally failed the NIH test panel, which includes both infectious and non-infectious samples. But Chiron’s detection method showed the highest “sensitivity and specificity” for the infectious samples yet achieved, according to the report.
VIRAL HEPATITIS
Viral hepatitis causes inflammation and swelling of the liver. In some cases, acute liver failure or chronic liver diseases, such as cirrhosis and liver cancer, may result. Symptoms of hepatitis include yellow skin, loss of appetite, fatigue and dark urine.
Researchers have identified five different viruses that cause hepatitis; additional hepatitis viruses are likely to be discovered.
Hepatitis A: A RNA virus that may be spread by direct contact with an infected individual or through food or water contaminated with feces. May cause epidemics. Frequently occurs in children and young adults. Is usually followed by complete recovery. Diagnosed by blood tests. Preventable by good personal hygiene and immune serum globulin injections. No specific treatment. Twenty-five thousand cases reported in the United States in 1987, most cases not reported.
Hepatitis B: A DNA virus that is usually spread by contaminated blood transfusions and intravenous needles, and intimate personal contact, such as sexual intercourse and spread from an infected mother to her newborn. Most infected individuals recover completely, but some become chronic carriers. Such individuals remain infectious to others; they may also develop chronic hepatitis, cirrhosis and liver cancer. Diagnosed by blood tests. Preventable by vaccination and immune serum globulin infections. Estimated 300,000 cases in the United States each year, about half of which cause symptoms.
Hepatitis C: Newly discovered RNA virus. Like hepatitis B, may be spread by contaminated blood transfusions and intravenous needles and, apparently, by intimate personal contact as well. In the United States, may be responsible for up to 80% of the cases of “non-A, non-B hepatitis” transmitted through blood transfusions and 50% or more of non-A, non-B cases acquired in the community. An estimated 150,000 non-A, non-B hepatitis cases occur in the United States each year, one quarter of which cause symptoms. Fifty percent or more of infected individuals develop chronic liver disease. Blood tests under development.
Hepatitis D: Also known as delta agent. An incomplete RNA virus that requires previous or simultaneous hepatitis B infection to infect liver cells. Most commonly found among intravenous drugs users and recipients of multiple blood transfusions. May be associated with an increased risk of chronic liver problems. Diagnosed by blood tests. No specific vaccine.
Hepatitis E: A RNA virus that is a common cause of sporadic hepatitis cases as well as epidemics in many Third World nations. Like hepatitis A, may be spread by direct contact and exposure to contaminated food or water. In some nations, may account for up to 50% of all acute viral hepatitis cases. Is usually followed by complete recovery. Discovered in 1986 by a research team led by Daniel W. Bradley of the U.S. Centers for Disease Control. Believed to be rare in the United States. Blood tests under development.
