Hepatitis C; The Uncovering of a Silent Killer


Imagine playing Russian roulette but this time, you get infected with a liver scarring virus. This was the case in blood transfusions in countries like Mexico where the chance of being infected by Hepatitis C virus, or HCV, among blood donors, are ranging between 0.74 and 1.5% and ∼2% in asymptomatic individuals. HCV is a serious public health burden with about 71 million people worldwide reported as chronically infected with most affected regions being the WHO eastern Mediterranean region with (21 member states including Afghanistan, Bahrain, Djibouti, Egypt, Iran) and WHO European region (with 53 member states), both having an estimated prevalence of 2.3% and 1.5% as of 2015.

Where it started

Rewind to the year 1976 where the Nobel Prize in Physiology and Medicine was awarded to the joint effort of Baruch S. Blumberg and D. Carleton Gajdusek concerning “new mechanisms for the origin and dissemination of infectious diseases”. During the 1960s, Blumberg identified a special antigen (which he called the ‘Australian antigen’) in the serum of a hemophiliac who had a history of being received several blood transfusions in the past when tested against the serum of Australian aboriginals (who had no such history of being recipients of a blood transfusion). On further observations, he was able to identify a certain correlation between the occurrence of this protein in the serum and a past case of a form of jaundice that occurred by means of an infection, then referred to as ‘serum hepatitis’.

This antigen, known as an HBs– antigen, was identified as a major protein in the hepatitis B virus that can be used for the screening of that form of hepatitis by the scientists at NIDDK (then called the National Institute of Arthritis and Metabolic Diseases).  This surface protein found in the virus is very much distinguished from the virus that causes Hepatitis A, which a most acute and treatable type of Hepatitis.

The discovery of viruses causing Hepatitis A and Hepatitis B during the mid-1970s the led to a greater reduction in post-transfusion hepatitis (PTH) cases – the cases where the recipients are found out to have contracted the disease through the transfusion despite the prior screening for the viruses in the serum of the donors. But it’s not quite a happy ending, yet. The discovery of the Hepatitis A and B viruses only helped the reduction of PTH cases by 25 to 50 percent, which suggested the presence of an unidentified third virus which is reportedly responsible for a greater number of chronic cases compared to hepatitis A or B. Harvey J. Alter and colleagues, who were studying the occurrence of PTH among recipients noticed this through methodical approach and identified this novel agent that was behind almost all of the PTH cases as a non- A non –B hepatitis (NANBH) virus. Further, he showed that chimpanzees are also susceptible to the virus by transferring the sera of an infected to a chimpanzee.

A novel approach to identify HCV

Michael Houghton and colleagues spent 6 years (1982 to 1988) in a laboratory at a newly formed biotechnology company at that time called the Chiron cooperation (founded in 1981); trying to uncover the identity of the novel NANBH virus using numerous molecular biological methods. These included the attempts of using hybridization probes from a variety of known viruses (such as flaviviruses, togaviruses, hepadnaviruses, picornaviruses, etc. ) to identify signals from the NANBH genome, usage of full HDV (Hepatitis –D virus) genome as a molecular probe for NANBH, development of silver staining technique to identify high molecular weight DNA and RNA viral genome those might’ve been present in NANBH infected chimpanzee materials and unsuccessful attempts of in-vitro cultivation of the virus in tissue culture systems looking for a cytopathogenic effect of some form induced by the replication of the virus.

Finally, a blind immunoscreening approach led to the identification of the Hepatitis C virus, the agent responsible for parenterally transmitted NANBH. This was done by first pelleting the virus and synthesis of cDNA (with prior denaturation since it wasn’t initially clear whether it was an RNA or a DNA that is going to serve as the template for the cDNA synthesis). The cDNA was inserted into a lambda gt11 vector to obtain the library of phage clones. The clone producing the fusion protein is then isolated through screening using the serum from a patient with NANBH which contains the antibodies produced against the agent. This led to the detection of a clone (named 5 -1 -1 clone) that was identified by the serum obtained from several patients. The clone was then proved to be derived from the HCV genome through cross-hybridization techniques.

Fig 1 – Isolation of clone 5-1-1 and identification of HCV

This led to the detection of other clones in the same library and these sequences hybridized to a 100,000 nucleotide containing RNA that was present in liver samples of chimpanzees those were infected with HCV. Gradually the complete nucleotide sequence of the virus is uncovered and the virus was identified as a flavivirus. Houghton and colleges were thus able to formally demonstrate that the HCV was the agent behind the transmission of NANBH, which is now termed as Hepatitis C.

The final proof

This proper discovery of HCV led to the development of diagnostic tests for the presence of the virus. In 1997 further breakthrough was achieved when Charles M. Rice was able to produce the first infectious clones of HCV that can be used to infect chimpanzees in order to study which cell lines could be used to grow the virus in the laboratory conditions. The chimpanzees showed the same symptoms as in a human patient which is shown as the final proof that HCV was the agent behind the mysterious PTH cases.

Fig 2 – Contribution by Harvey J. Alter, Michael Houghton, Charles M.Rice to the discovery of HCV

The discovery of HCV, without a doubt, has dropped the number of PTH cases to near zero. Furthermore, this discovery is a major stepping stone in the development of blood tests that reduces the risk of getting infected by hepatitis through blood transfusion and also lead to the development of drugs that can cure the disease. The painstaking effort and time for the discovery of HCV are well acknowledged by being awarded the Nobel Prize in Medicine and Physiology, 2020.


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