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ABCs of Hepatitis Revealed |
Encouraged by successful pinpointing of the hepatitis B virus , many researchers pursued research aimed at learning more about the hepatitis A virus as well as other suspected hepatitis viruses. In 1973, Stephen M. Feinstone and colleagues at NIH used an electron microscope to visualize viral particles in the stools of infected individuals. At about the same time, Hilleman and colleagues at Merck defined and characterized the human hepatitis A virus that Feinstone had purified from the infected livers of marmosets, a type of monkey. By 1996, Hilleman and his colleagues had made an attenuated hepatitis A vaccine (that is, a vaccine made from a virus that is modified in such a way that it cannot cause disease) that was licensed for general use. Another hepatitis A vaccine was developed by SmithKline Beecham Laboratories.
In 1978, Italian gastroenterologist Mario Rizzetto and molecular virologist John Gerin, of Georgetown University, discovered the delta, or hepatitis D, virus. This rare virus depends on hepatitis B to survive and in combination with hepatitis B causes a much more severe form of the disease. In 1983, Mikhail Balayan of the Institute of Poliomyelitis and Viral Encephalitides in Moscow discovered hepatitis E virus. Like hepatitis A, hepatitis E is spread by contaminated food and water and is usually found during localized epidemics.
Despite blood screening for hepatitis B, some patients still came down with posttransfusion hepatitis due to what was termed "non A-non B" hepatitis. Scientists suspected that yet another virus or viruses could be transmitted via blood and turned their attention to developing strategies first to isolate non A-non B hepatitis and then a test to identify it in blood. After reaching those milestones, they hoped to someday work toward developing a recombinant vaccine. But the non A-non B hepatitis agent proved especially elusive. In 1983, Chiron Corporation began supporting a large research program to solve the puzzle, involving a collaboration between Daniel Bradley at the Centers for Disease Control and Prevention and Michael Houghton, George Kuo, and Que Lim Choo and colleagues at Chiron. Bradley, who had been studying chimpanzees infected with human serum containing non A-non B hepatitis agent or agents, provided contaminated chimpanzee sera to Chiron. In 1989, Michael Houghton and colleagues ushered in a new era for the discovery of infectious agents when they used molecular biological techniques to clone hepatitis C, the agent responsible for 80 to 90 percent of non A-non B hepatitis. This was a scientific tour de force because the unknown agent, unlike the other hepatitis viruses identified up to that point, had not been visualized, grown in culture, or immunologically defined. Following the introduction of sensitive and effective blood tests for the detection of hepatitis C in 1990, the risk of transfusion-related hepatitis is now in the range of one in 100,000 units transfused.
The discovery in the past 30 years of these hepatitis viruses and promising developments in blood screening and vaccines lead researchers to hope that viral hepatitis will soon be controlled and will no longer be the threat to human health it has been for thousands of years.
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 | | | All About Blood - From the American Association of Blood Banks. This site has information about blood, blood banking, and blood screening--and a page on the highlights of transfusion history. |  | | Hepatitis B - More information on Hepatitis B from the American Liver Foundation. | | | Understanding the Immune System - A detailed introduction to the immune system, including a section on antibodies. | | | Yellow Fever and the Reed Commission - An interesting historical article on yellow fever and the Spanish-American War. |  |
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