Ethics of Research involving animals
The discovery of the hepatitis C virus using the chimpanzee
6.25 We now consider a more historic example of animal research for the study of disease. The existence of a blood-borne hepatitis virus that was neither type A nor B was described in the 1970s, following the identification of both these types. Throughout the 1980s, assays were developed to try and identify the cause of what was then termed non-A, non-B (NANB) hepatitis. However, none of the tests were sufficiently reproducible or specific.23 Therefore an experimental chimpanzee model was developed, as this species was the only non-human animal that could be infected with the NANB hepatitis agent, which is still not able to be propagated in vitro. The chimpanzee model was used to demonstrate that NANB hepatitis was indeed transmissible, and allowed the isolation and characterisation of the virus.24
Researchers used large volumes of blood from an infected chimpanzee with a high level of infection to isolate the virus. Proteins in the chimpanzee blood were then screened against serum from a NANB hepatitis patient, which was expected to contain anti-NANB hepatitis antibodies. Eventually a NANB hepatitis viral protein in the chimpanzee blood was found to react with antibodies from the human patient, possibly due to the high levels of viral particles in the chimpanzee blood. With the genome available, it was possible to develop reliable diagnostic tests for what was subsequently termed hepatitis C. Treatment strategies have also been developed in animals although a vaccine does not yet exist.
6.26 The animals in the study described above could be expected to suffer symptoms similar to those experienced by humans, especially at high infection doses. According to the US National Center for Infectious Diseases, 80 percent of people with hepatitis C have little or no signs or symptoms, whereas others may experience jaundice, fatigue, dark urine, abdominal pain, loss of appetite, nausea and eventually chronic liver disease.25 Additional implications for welfare relate to the long-term husbandry of the infected animals as they may be infectious to other animals and to humans, and must therefore be kept in single housing.
6.27 The major cause of hepatitis C infection was formerly blood transfusion.26 It is now routine to screen donated blood for hepatitis C, which has vastly reduced transfusion-mediated infection in industrialised countries. The discovery and characterisation of the virus, its role as the etiological agent and the mechanisms whereby it produced disease in chimpanzees led to an understanding of the primary role of the virus in post-transfusion hepatitis and its tendency to induce persistent infection and chronic liver disease. Approximately 170 million people worldwide are chronically infected with hepatitis C,27 many of whom will develop cirrhosis and liver cancer.
6.28 Because of the long asymptomatic period (up to 20 years), most infected people are unaware that they carry the virus and continue to be a source of new infections. Diagnostic assays to detect the virus are therefore essential to identify these patients. Current work on chimpanzees is not permitted in the UK, as the Home Office does not grant licences for research involving the great apes (see paragraph 13.6). Without the research described above, very little would be known about hepatitis C, and diagnostic tests would not be available. Many scientists believe that the lack of a reliable animal model other than the chimpanzee is the single greatest barrier blocking the development of a safe and effective vaccine.
Footnotes25 National Center for Infectious Diseases (2005) Viral Hepatitis C, available at:
http://www.cdc.gov/ncidod/diseases/hepatitis/c/fact.htm. Accessed on: 26 Apr 2005.
26 Alter HJ, Purcell RH, Shih JW et al. (1989) Detection of antibody to hepatitis C virus in prospectively followed transfusion
recipients with acute and chronic non-A, non-B hepatitis N Engl J Med 321: 1494–500.
27 World Health Organization (2000) Fact sheet No. 164 Hepatitis C, available at:
http://www.who.int/mediacentre/factsheets/fs164/en/. Accessed on: 26 Apr 2005.