Hepatitis B Virus Linked to Liver Cancer in U.S. Asians
A Los Angeles physician is concerned that thousands of babies born of Asian mothers in Southern California and elsewhere in the United States are unnecessarily at risk of developing liver cancer.
The reason, said Dr. Myron J. Tong, is the high incidence of hepatitis B in many parts of Asia. Federal health officials now consider hepatitis B to be a potent precursor of liver cancer in those people who also are carriers of the hepatitis B virus.
Tong, a professor of medicine at the USC School of Medicine and chief of the liver center at Huntington Memorial Hospital in Pasadena, is taking part in a three-city study aimed at preventing liver cancer cases that are triggered by chronic hepatitis.
Tong’s studies show that in contrast with the general population of the United States, the hepatitis carrier rate among people now living in this country but who were born in Asia is very high. For instance, 12% of Asians living in Los Angeles but born in China, Taiwan, Hong Kong, Laos, Vietnam or Cambodia are hepatitis B carriers, the studies indicate. The carrier rate for the general U.S. population ranges from 0.1% to 0.5%.
Transmitted by Blood
Hepatitis B, once called serum hepatitis, is one of several types of the disease. But unlike another common type, hepatitis A, the B type is transmitted by blood, not by contact with feces or by food or water. Besides blood transfusions, hepatitis B can be acquired through sexual intercourse--particularly between sexually active male homosexuals--and by contaminated needles among intravenous drug users.
But Tong’s current concern is with pregnant women who are carriers of the disease. At the time of delivery, the virus is passed from the mother to the newborn infant.
Most babies may never develop any symptoms indicating they have become infected, but Tong said in a recent interview that up to 90% of them will become carriers. While not all carriers develop liver cancer, their chances of doing so, perhaps 30 years later, are 225 times greater than for people who are not carriers, the physician said.
In Taiwan, where Tong has done research on the association between liver cancer and hepatitis B, liver cancer is a leading cause of death, as it is in most of Asia.
Identify Female Carriers
The key to preventing both the hepatitis B infection and possible future liver cancer, as Tong and other researchers in San Francisco and New York believe, is to identify all female carriers of childbearing age and take certain steps that are now available to prevent the mother’s virus from infecting the baby.
These steps, according to the recommendation of the federal Centers for Disease Control, are for the baby to receive an injection of gamma globulin within 24 hours of birth, followed six months later with the recently developed hepatitis B vaccine.
However, Tong noted that the preventive procedures are so new to most physicians that only a handful make use of them.
“We are trying to educate doctors now,” he said. “We are bothered that many clinicians who must become aware are not yet aware.”
Some doctors, however, say that physicians may be reluctant to use the hepatitis B vaccine because of concern over its safety--concerns that the U.S. Public Health Service says are without basis. They arise from the fact that when the vaccine was under development in the late 1970s, male homosexuals were the chief donors of the blood products from which the vaccine is derived.
Several years later homosexuals were found to be suffering from a new disease that subsequently came to be called AIDS, or acquired immune deficiency syndrome. From the beginning, researchers suspected that AIDS was caused by a virus, leaving open the possibility that the virus may have contaminated the hepatitis vaccine.
Subsequent studies, however, have convinced public health authorities that no virus, including the agent that causes AIDS, can withstand the inactivation process used in making the vaccine.
“There is no evidence that the causative agent of AIDS has been transmitted by (the hepatitis B vaccine),” the Centers for Disease Control stated two months ago in its latest recommendations for protection against hepatitis B.
To speed use of the vaccine, Tong said he is considering approaching legislators in Sacramento to convince them that the public health benefit is great enough to justify requiring all pregnant women to be blood-tested to see if they are hepatitis B carriers. At present, tests are mandatory only for syphilis, Rh factor and rubella (German measles).
Study Conclusions
Tong said studies on the relationship between hepatitis B and liver cancer indicate that 85% of the liver cancer cases that are due to this relationship could be eradicated within a single generation if the proper preventive measures were followed.
Blood tests that he and his colleagues have conducted on 9,000 Asian women of childbearing age who live within a 10-mile radius of Huntington Memorial Hospital, where the local study is centered, indicate that 12% are hepatitis B carriers.
Using 1980 statistics, the physician said that about 9,300 of the 125,000 Asian women of childbearing age in Los Angeles County can be expected to pass the virus on to their babies unless steps are taken to thwart the disease. Considering the large influx of Vietnamese and other Asians since 1980, the number now is even larger, he said.
According to statistics provided by the Centers for Disease Control, 661,963 Asian refugees were resettled in the United States between 1975 and 1983.
In China, where half of all the liver cancer in the world occurs, the disease is the third-leading cause of cancer deaths, according to Dr. Brian Henderson, director of the Norris Cancer Hospital and Research Institute at USC.
Two years ago during a research project in Guangxi province in China, Henderson helped to establish the role that hepatitis B plays in causing liver cancer. The disease is so prevalent in Guangxi--26% of the residents are hepatitis B carriers, according to Henderson--that liver cancer there accounts for one-half of the deaths from all causes.
Because of the high cost of the hepatitis B vaccine manufactured in Western countries, Henderson said, the Chinese government is using a loan from the World Bank to set up its own facility to make the vaccine.
Health officials there see the vaccine as a promising way to virtually eliminate a major form of cancer, according to the cancer specialist.
China and the rest of Asia are not the only parts of the world where hepatitis B is widespread. It, and liver cancer, are also common illnesses in Africa and the Pacific islands.
Speaking at a recent conference on liver disease at USC, Dr. Michael C. Kew of the University of Witwatersand in South Africa said that the hepatitis virus appears to be spread differently in Africa than in Asia.
Contaminated Instruments
Unlike Asia, where most people appear to acquire the hepatitis B virus from their mothers, Kew’s studies indicate that in Africa contaminated instruments used by medicine men and others in scarification practices in rural areas play a major role in transmitting the blood-borne disease. Biting insects, like mosquitoes and bedbugs, may also be important spreaders of the virus from one person to another, according to Kew.
In addition, Kew said, there is strong evidence that a potent carcinogen, known as aflatoxin, works in conjunction with the hepatitis virus to increase the Africans’ chances of developing liver cancer. Aflatoxin is a fungus that grows on peanuts, a common food in much of Africa.
In the United States, where blood transfusions were once the principal method of acquiring hepatitis B, a test that detects the virus in a donor’s blood has reduced the spread of the disease by that route. The death rate from liver cancer has dropped about 40% over the last 35 years.
But experts predict that the number of liver cancers may soon rise again as the effects on the liver of recent increases in hepatitis B cases begin to appear.
The hepatitis B rate has doubled since 1974, partly because of immigration from Asia and partly because of the high rate of the disease among intravenous drug users and male homosexuals. The carrier rate among gays, for example, is 5%--a third that of Asians but at least 10 times that of the general population.
